In this chapter we will first recall the motivation behind the task of unambiguous, systematic and machine-processable explication of knowledge about socio-cultural time that is related to nations, religions and business life & education. Then, we will discuss our proposal that encourages devising two separate domain-specific ontologies to accomplish this task. We will justify the need for two ontologies, clarify their position with respect to each other and focus on one. We will define the role of the first ontology, which is the Ontology of Socio-Cultural Time Expressions. We will proceed with stating the purpose and the scope of the second ontology, which is the Ontology of Socio-Cultural Time Concepts. We will go into the details of this ontology as it comprises the focal point. Finally, we will show the realized and possible applications that use the focal ontology. We start with the definition of socio-cultural time.

 

The Russian sociology professor Pitirim Sorokin was the first person to mention about socio-cultural time in his book “Socio-Cultural Causality, Space, Time” [82]. Here, Sorokin argues that the way a specific culture conceives of causality, space, and time is not the same as natural science conceptions and must be understood in relation to the specific socio-cultural context. Consequently, he suggests there are two different conceptions of time. One is as we understand it in natural science. Second conception on the other hand, exists independently of the first one and it is necessarily culture dependent. Sorokin defines the second conception of time as socio-cultural time.

 

“Within the same territorial aggregate composed of different religious, occupational, economic, national, and cultural groups, there are different rhythms and pulsations, and therefore different calendars and different conventions for the sociocultural time of these groups. Compare a Harvard calendar with one operating, say, among factory workers. The calendar of the Roman Catholics in Boston--in part, at least--is different from that of the Protestant Bostonians.  Side by side with quantitative time (which itself is in a degree a social convention), there exists a full-blooded sociocultural time, with all its ‘earmarks’: it is qualitative, it is not infinitely divisible, it does not flow on evenly; it is determined by social conditions, and reflects the rhythms and pulsations of the social life of a given group”

 

Different social groups and different cultures have different conceptions of time, as a result of which complexities arise. Let us return to our example with the weekend; in most western cultures the expression “Weekend” is used to refer to the two consecutive days of Saturday and Sunday w.r.t. the Gregorian calendar.

 

In our regard, such use of the expression “Weekend” refers to the time period of two days that are reserved for leisure time, when one in most of the cases does not have to work (we acknowledge that there are exceptions such as museum workers, healthcare workers, sales personals etc, who work on the “Weekend”). The expression “Weekend” in Islamic and Jewish cultures though, refers to the two consecutive days that are again associated with leisure time and with exemption of work, but this time the two days are Friday and Saturday.

 

Clearly, the conception of time underlying the expression “Weekend” is different in the related cultures. In one culture, it denotes the concept of a time period that corresponds to the 5^th and 6^th days of a week w.r.t. the Gregorian calendar and in the other culture it corresponds to the 6^th and 7^th days of the week. Hence, in Israel or in Turkey[1] there is a different time conception of Weekend than that of in Germany. It could be helpful to acknowledge this fact when scheduling appointments “for the weekend”. Let us consider another example, the concept of Summer Semester in higher education. In Turkey, there is not a concept of Summer Semester because summers are too hot to allow any form of study or lecture. Instead, the Academic Year is partitioned into two semesters, which are the First Semester and the Second Semester. The Second Semester ends around the middle of June before the hot summer time starts. Now a German student, who has done all his plans according to doing an exchange semester in Turkey during summer, would be surprised to find out in the end that this is not possible at all. In the Turkish culture, there is no such concept as Summer Semester. Similarly, a Turkish student, who wants to have an exchange semester in Germany may sit and wait the summer to be over to be able to start studying, whereby wasting a lot of time.

 

Due to the rapid developing technology, today the interaction between people from different socio-cultural contexts is very high. However, different people may have different conceptions about the real world and a reason for this is the different socio-cultural contexts that the people belong to. Such conceptions are implicitly present in people’s minds. In most cases, each socio-cultural group takes its conception of a matter as a benchmark and assumes that the members of the other socio-cultural group would share the same conception. As Sorokin points out and as the above examples illustrate, same is the case with the conception of time.

 

False assumptions as above and the consequent communication problems could be avoided if the implicit conceptions of time are made explicit and shared with others. In the real world there are books, workshops, courses, seminars and even departments at universities such as intercultural communication or cross-cultural communication that are aimed at capturing such knowledge, making it explicit and sharing it with others.

 

In this thesis, we assume that in a multi-cultural environment such as the Web, where the interaction between people from different socio-cultural contexts and the interaction between the Web application systems developed by them according to their context specific needs are extremely high, complexities similar to those in the real world arise. That is, communication and cooperation problems due to the lack of understanding and recognizing the different conceptions of time. Therefore, we believe in the need for explicitly defining knowledge about socio-cultural time for the Web, just like the books, courses and lecturers do it for the real world.

 

Starting out with this motivation, we have defined our task as providing a formal, explicit, unambiguous and systematic description of knowledge about socio-cultural time related to nations, religions and business life and education for the Web. Our goal is to support temporal Web application systems such as automated appointment schedulers with socio-cultural conception of time, so that they can react in a more sensitive way to the users’ culture specific needs and expectations. During our research we have not come across to a formal and machine processable description of this kind of temporal information for the Web.

 

We believe appointment scheduling is a task, where different conceptions of time can be observed frequently and where they play an important role. In [79] Spranger describes the characteristics of such a Web based appointment scheduling system by means of scenarios, provides examples of some currently used schedulers and illustrates the system’s global structure. Furthermore, she points out to the fact that the scheduling systems in question “are mostly limited to one calendar system and a particular representation scheme”. So, they do not consider the socio-cultural conception of time.

 

Let us reconsider the two examples above within the context of the Web and assume that scheduling an appointment for the weekend and searching for an appropriate exchange semester in summer are done by temporal Web applications such as automated appointment schedulers and automated student exchange finders that do not require human intervention.

 

Clearly, such an application needs the same information as humans, namely the information about socio-cultural time. Only then it can reason that weekend as a concept is not absolute but it is relative to a given culture, that the concept of Summer Semester cannot be found in every culture and that Turkey is one such culture and so forth.

  

Given this picture, there are at least two requirements for a temporal Web application system such as the automated appointment scheduler to be able to make use of the knowledge about socio-cultural time. First, the knowledge should be defined in a very formal, explicit and unambiguous way, in other words it should be formal enough to be machine processable. Second, it should be accessible to the Web application system. Ontology fulfils both requirements; it provides unambiguous, formal and machine processable description of any domain and it is accessible to any Web application system once it is published on the Web. Therefore, a domain ontology that formally describes the socio-cultural time can help overcoming communication and cooperation problems on the Web that can arise due to differing time conception of heterogeneous cultures and social groups.

 

The domain of socio-cultural time is very broad as it covers the time conception of every culture and every social group. In [79] Spranger provides a hierarchical structuring of the domain of socio-cultural time. In other words, she demonstrates how general and how specific a time conception can be, based on socio-cultural characteristics. Accordingly, the top-level category is a universal calendar system that is adopted by a large group of cultures and social groups. At the lower levels there are calendar systems, which are based on time conceptions of countries, states, regions, business enterprises and academic institutions. Finally, the lowest level representing the most specific calendar system, is the one from an individual person reflecting own socio-cultural conception of time based on own social context and individual specifications.

 

In this thesis, we restrict the domain to a subset of socio-cultural time that is related to nations, religions and business life & education. There are two reasons for deciding for these socio-cultural groups; first we believe that in real life knowledge about socio-cultural time is very often embedded in these particular socio-cultural groups. Second, we predict Web applications such as automated appointment schedulers that this ontology aims to support, would be most appealing to the specific social group of business people and academia of different nations and religions.

 

Within this context, we have paid specific attention to the Turkish, US American and Israeli nations, the Islamic, Christian and Jewish religions and the social groups of secondary and higher education as well as the group of business people. In our regard, Islam, Christianity and Judaism represent three most widespread religions of the world, Turkish, US American and Israeli nations represent three considerably big nations, which are also mainly associated with the three religions. The social groups related to secondary, higher education and business life exist almost in every culture. Although we have restricted our model to a subset of the domain, it can be easily extended to include other socio-cultural groups.

 

For example, those related to sports, history, politics and healthcare, those related to Hindu or Buddhist religions or Japanese nation and so forth.

 

As we have discussed in the previous chapter, information about the conceptual structure of the real world can be discovered in the expressions of the natural language. Therefore, we believe we can acquire knowledge about socio-cultural time by looking at the language expressions used to talk about time by various cultures and social groups. For example, expressions such as “Tea Time”, “Thanksgiving Day”, “School Year”, “Sabbath” demonstrate different cultures’ understanding of time. When we hear “Tea Time” we presumably think of a period of time that is reserved for the activity of drinking tea and we implicitly associate it with England. Similarly, when we hear “Thanksgiving Day”, we presumably think of a period of a day associated with USA and with eating a turkey etc. Put in a very simple way, if we want to learn how different cultures and social groups think about time, we can listen to how they talk about it.

 

Concepts of socio-cultural time periods are denoted by the socio-cultural time expressions. Let us explain this. We stated above that socio-cultural time expressions give us information about how different cultures and social groups conceive of time. Moreover, the expressions themselves do not precisely and unambiguously describe the meaning. In other words, we can hear the expression but to be able to make sense of the expression we need to know the definition of the concept of time that the expression refers to. Thus, the expressions used for talking about time only deliver us the information about how the speakers conceive of time in their particular socio-cultural context but they do not unambiguously describe what their meaning is. For that, the concept behind the expression needs to be investigated.

 

If we consider the expression “Thanksgiving Day” again, we see that it is composed of two words “Thanksgiving” plus “Day”; it is in English and so forth. Nevertheless, this does not suffice for a precise and systematic description of the meaning. The meaning of the expression is implicitly present in our minds; upon hearing it we associate it with the concept of a time period of one day that is specific for USA. With such an association, we are relating the expression we have heard to the specific concept of time, in other words we are referring to the concept that the expression denotes. Thus, in order to understand the meaning of the expression and to make sense of it, we are looking at its denotation.

 

If we reconsider our goal, which is providing unambiguous, explicit, formal and machine-processable description of knowledge about socio-cultural time, so that it can be used to support temporal Web application systems it is clear that this can only be achieved by referring to the denotations of the socio-cultural time expressions. Therefore, an ontological model at the conceptual level is necessary.

This requirement essentially directs us to the modelling approach we have discussed in the previous chapter. Hence, we are distinguishing between a conceptual level and a lexical level for representing the domain of socio-cultural time. We understand socio-cultural expressions of time at the lexical level and socio-cultural concepts of time at the conceptual level, as being complementary to each other. As a result of this approach, two separate ontologies have been designed and implemented, which are the Ontology of Socio-Cultural Time Expressions and the Ontology of Socio-Cultural Time Concepts.

 

The first ontology is a formal representation the socio-cultural time expressions found in the natural language and it does not attempt to provide an unambiguous description of their meaning. On the contrary, it has the purpose to demonstrate the ambiguity present in the socio-cultural time expressions. The second ontology on the other hand, is a formal and unambiguous explication of the meaning of the socio-cultural time expressions.

 

Once again, our goal is to provide a precise and unambiguous definition of the knowledge about socio-cultural time to support temporal Web application systems, so that they can react more sensitively against the context specific needs of their users. Therefore, we are interested in the meaning of socio-cultural time. Given these facts, the Ontology of Socio-Cultural Time Concepts will comprise the focal point of the chapter.

 

Following general requirements hold for both ontologies:

 

1.      Typing: Entries in the ontology need to be typed to reflect the differences between the main categories. For example, category Socio-Cultural Time Expressions and category Calendar Date Expressions are two distinct types. Consequently, one instance cannot be an instance of both categories (exception: some instances in the Ontology of Socio-Cultural Time Expressions do belong to several categories in order to demonstrate the ambiguity of the socio-cultural time expressions).

2.      Category Combination: It should be allowed to combine existing categories in order to yield new categories. For example, combining the category Socio-Cultural Time Expressions Related to Nations with the category Socio-Cultural Time Expressions Denoting a Time Period of One Day should yield the category Socio-Cultural Time Expressions Related to Nations Denoting a Time Period of One Day.

3.      Stability: Local changes should not affect the other parts of the ontology, i.e. additions and deletions in one category should not lead to changes in other categories.

4.      Extensibility: It should be possible to extend the ontology at arbitrary depth and branching level.

5.      Graph Structure: It should be possible to find an entry (either a time expression or a time concept) starting out from different categories. Therefore, multiple parents should be allowed and the model should have the form of a DAG (not a tree).

In the next sections we will mention the role of the Ontology of Socio-Cultural Time Expressions and study the details of the Ontology of Socio-Cultural Time Concepts.

 

There are some naming conventions for both ontologies. As a rule, names of the categories start with a capital latter as in Socio-Cultural Time Expressions Denoting Time Periods. Names of instances also start with capital letters, however the instances of the Ontology of Socio-Cultural Time Expressions will be quoted. For example, string Holiday will be represented as “Holiday” if it is an instance of the Ontology of Socio-Cultural Time Expressions. It will be represented as Holiday (without the quotes), if it is an instance of the Ontology of Socio-Cultural Time Concepts. Names of properties (attributes) and names of relations begin with lowercase letters, whereby in most of the cases property names have the prefix has- as in has Duration or in has Granularity. Names of relations also start with lowercase letters as in subclassOf.

 

In order to profit from the existing guiding services provided for ontology development process, we have adopted METHONTOLOGY methodology to a large extent for the construction of the two ontologies. METHONTOLOGY has been chosen because it provides a clear-cut definition of what steps to take during the ontology construction process, in particular during the conceptualization of the ontology. Subsequently, it is possible to provide a formal description of the domain socio-cultural time related to nations, religions, business life & education that is independent of languages and implementation platforms. In the next sections we will observe the specification, the conceptualization and the implementation processes of the Ontology of Socio-Cultural Time Concepts w.r.t. METHONTOLOGY.

 

OWL has been chosen as the ontology language for the formal implementation of the two ontologies out of two reasons: first both ontologies are designed to support Web-based applications, therefore any ontology language would not do. It had to be an ontology language for the Web. Second reason is that OWL is the latest standard for developing ontologies for the Web and it is expressive enough for our purposes. As we have seen, sophisticated tools also exist for editing OWL ontologies. Protégé 2000 has been used as the ontology editor because of the OWL support it provides and the frequently updated discussion list it maintains.

 

The structure of this chapter is as follows: this introductory section has provided a definition of the domain socio-cultural time and it has recalled the motivation for providing a systematic and unambiguous explication of knowledge about socio-cultural time. It has represented our approach for such an explication and it has given a brief overview of the two ontologies that have been designed and implemented. The means that have been initiated for the development of the two ontologies have also been mentioned.

Subsection 5.1. Role of the Ontology of Socio-Cultural Time Expressions gives a detailed explanation of the role of the related ontology within the whole context of the thesis. Subsection 5.2 Purpose and Scope of the Ontology of Socio-Cultural Time Concepts specifies the purpose and the scope of the related ontology and demonstrates the Specification Document of the ontology. Section 5.3 Conceptualization of the Ontology of Socio-Cultural Time Concepts presents a partial Glossary of Terms, Concept Classification Hierarchy, Concept Dictionary, Binary Relations Table and Diagram and the Instances Table of the related ontology. 5.4 Implementation of the Ontology of Socio-Cultural Time Concepts shows the OWL implementation of the ontology. Section 5.5 Applications discusses the possible and the realized applications of the Ontology of Socio-Cultural Time Concepts. Here, we will present how we have extracted some parts of the ontology, for example, a subset of socio-cultural time periods by using the RDF query language RDFQL on the OWL model and how we have built a small PROLOG database with the extracted socio-cultural time periods. Such a database can provide the basis for a socio-cultural Web calendar, which in return can support an automated appointment scheduling service for the Web.

 

5.1	Role of the Ontology of Socio-Cultural Time Expressions Related to Nations, Religions, Business Life & Education

 

The goal of this section is to clarify the role of the Ontology of Socio-Cultural Time Expressions within the context of the thesis. Thereby, we will give an overview of the contents of the ontology in terms of its categories, relations and instances. The relationship between the current ontology and the Ontology of Socio-Cultural Time Concepts will also be discussed. In a number of classification hierarchies some extracts of the ontology will be depicted.

 

Ontology of Socio-Cultural Time Expressions is a formal representation of a subset of the natural language expressions of time that are related to nations, religions, business life & education. For example, “Halloween” is an expression that is specific for the US American nation, “Christmas” is an expression related to the Christian religion, “Meeting” as an expression is very often used among the social group of business people, “Academic Semester” is an expression used by the specific social group of academia, and so forth. We call such expressions socio-cultural time expressions or expressions of socio-cultural time. As such, the Ontology of Socio-Cultural Time Expressions defines appropriate categories, to which these expressions can be assigned and it organizes the categories containing the expressions in a hierarchical order.

 

Expressions of socio-cultural time comprise the first of the two partitions of the domain of socio-cultural time related to nations, religions, business life & education and it corresponds to the lexical level. This means the Ontology of Socio-Cultural Time Expressions does not does not attempt to provide an explicit and an unambiguous description of the meaning.

 

Socio-Cultural time expressions, as expressions of the natural language, deliver us information about the conception of socio-cultural time. As we have stated, in our regard, by looking at how different social groups and cultures talk about time, it is possible to gain insight to different socio-cultural groups’ understanding of the concept of time. In other words, we want to understand the conception of time in a socio-cultural context, but in order to be able to get there we first need to look at the expressions about socio-cultural time. With this idea in mind, the Ontology of Socio-Cultural Time Expressions has been developed.

 

Recapitulating Chapter 4, we have referred to the ambiguity of the expressions of natural language, in particular to the ambiguity of socio-cultural time expressions. We have seen that one expression may denote several concepts and we cannot always precisely determine which concept is being referred to. The role of the Ontology of Socio-Cultural Time Expressions is about demonstrating this case. Thus, this ontology has the purpose to represent the ambiguous nature of the socio-cultural time expressions without attempting to explicate their meaning.

 

In the Ontology of Socio-Cultural Time Expressions, difficulties arose when assigning the expressions to appropriate categories because several of them possess more than one meaning. That is, most expressions denote more than one concept. This situation brings about the need for deciding for one meaning i.e. for one concept, but such a decision concerns the conceptual level. Consequently, the Ontology of Socio-Cultural Time Expressions exhibits one more time the need for the Ontology of Socio-Cultural Time Concepts.

 

Let us look at some entries in the ontology as well as at the problems we have come across to. Consider the socio-cultural time expression “Sabbath”. At the lexical level, Sabbath is an expression predominately used by the Jewish religion and the Israeli nation. Occasionally, one can hear it being used in other socio-cultural groups. Complexities arise, when we look at the meaning of the expression “Sabbath”. If we consider “Sabbath” as a member of the set of Jewish-Israeli time expressions, then we are referring to a concept of time that is one day long, that repeats every week and that is always on the 6^th day of the week. Moreover, according to the Jewish religion, the concept of Sabbath is associated with a holy day, during which one is exempt from work.

 

 

Considering the use of “Sabbath” in other cultures, however, we see that it may refer to another concept of time that is most probably but not necessarily one day long and that implies one’s personal decision to take a day off. It can also be used to mean one’s engagement in a work activity other than the regular work for that day. Clearly, the expression “Sabbath” denotes at least two different concepts.

 

Another example of an ambiguous socio-cultural time expression is “Holiday”, which is an expression used in many languages. According to our observations, this expression is mostly used to indicate some time off due to a specific celebration or out of personal reasons. However, the actual meaning of the expression “Holiday” is very is vague. It denotes many different concepts of time that are all necessarily periods of time but are very different in character. According to Merriam Webster’s Dictionary, the expression “Holiday” has at least three senses:

 

1.      Holy Day: a day set aside for special religious observance.

2.      a day on which one is exempt from work; specifically a day marked by a general suspension of work in commemoration of an event.

3.      a period of relaxation  (vacation).

 

For example, we can call Christmas as “Holiday”. Suppose that we find ourselves in late December of a given year and we ask for the “Holiday” plans of a friend of ours. Obviously, here we use the expression “Holiday” to refer to the event of celebrating Christmas and to the time off, which is during and after that event. Now suppose that we are in summer and we are again asking the same question to a friend. If the friend is a business colleague, then with the expression “Holiday” we probably refer to the time concept of Business Vacation that the colleague is going to have. If the friend is a student, then it is very likely that we use the expression “Holiday” to mean Semester Break, which is a period of time when no classes are held. As it can be observed, putting the expression “Holiday” into the perspective of different cultures and social groups, we obtain many different denotations.

 

As exciting as it is, this situation brings us into a state of ambiguity, where we need to decide for one meaning to avoid confusion and to provide consensus. Socio-cultural time expressions denote concepts and refer to the meaning but they do not provide an explicit and unambiguous description of the meaning. Hence, we could classify socio-cultural time expressions according to “the ways we talk about them”. On the basis of the concepts they denote, socio-cultural time expressions could be classified as “old-fashioned socio-cultural time expressions” (e.g. Lord’s Day for Sunday), “modern socio-cultural time expressions” (in this case Sunday for Lord’s Day), “socio-cultural temporal expressions of slang” (e.g. bigtime, ace time) to present how people with different socio-cultural backgrounds talk about time. Yet, all these would not suffice to deliver us the precise and unambiguous meaning. To put it briefly, the problems we have discussed demonstrate that there is not always a one-to-one relationship between socio-cultural time expressions and the time concepts they denote. In other words, it is not the case that always one expression denotes one concept. Instead, the relationship is frequently one-to-many, where one socio-cultural time expression denotes many socio-cultural time concepts.

 

As long as the meaning of a socio-cultural time expression is not clarified, that is, as long as it is not pinned down what concept or concepts the expression denotes, it is not possible to provide a systematic and unambiguous description of the domain of socio-cultural time related to nations, religions, business life & education. Moreover, if one socio-cultural time expression denotes more concepts, it is necessary to decide on one concept w.r.t. its relevance to the domain. Otherwise, it will not be possible to eliminate the ambiguity and to provide consensus about the domain. Yet, precise and unambiguous description of the domain as well as providing consensus about the understanding of the domain is the precondition for supporting temporal Web applications such as automated appointment schedulers. Without this, the reasoning components of such applications may have difficulties in drawing the necessary conclusions, due to the imprecise definition and the ambiguity of the information about the domain.

 

In sum, the Ontology of Socio-Cultural Time Expressions as is, demonstrates the need for a conceptual level to enable a precise description of knowledge about socio-cultural time related to nations, religions, business life & education. In the following subsection, we will discuss the purpose, the scope and the contents of the Ontology of Socio-Cultural Time Concepts that has been developed as an answer to the need for the conceptual level. Before proceeding to that, we introduce the Ontology of Socio-Cultural Time Expressions briefly.

 

The hierarchical structure of the Ontology of Socio-Cultural Time Expressions has the form of a graph (DAG). The top level category (a category is sometimes called class or concept but here we will adopt the term category) is (┬). All other categories are subcategories of (┬), that can be combined to obtain further categories, when necessary. As we have stated, the Ontology of Socio-Cultural Time Expressions does not suffice to provide an explicit and unambiguous description of the meaning of the expressions. However, in order to be able to determine the categories of the ontology and to be able to assign the expressions to appropriate categories, we do refer to the meaning of the expressions.

 

Top level category is divided into one subcategory; it is the category Time Expressions Denoting Time Periods. As such, this category includes all possible expressions about time, which denote concepts of time that can be explicitly anchored on the time line. Examples are expressions about, calendar dates, days of weeks, months, hours of days, years, centuries also expressions such as “Midnight”, “Yesterday”, “Next Year”, “1700s”, “60s”, “Medieval Ages”, “17th century”, “Lunch-Time”, “Weekend”, etc. The expressions about time, which denote concepts that cannot be explicitly anchored on the timeline, are not within the scope of the ontology. Examples of such expressions are “Sometime in Future”, “A While Ago”, “Whenever Possible”, “Way Before”, etc.

 

Subcategories of one category are at the same level and they have the same criterion of subdivision. To determine the criterion, we ask the question at the category Time Expressions Denoting Time Periods “Does the time expression denote merely a calendar date time period, or does the expression denote a time period that is related to one of the socio-cultural groups specified within the scope of the ontology?” Consequently, all time expressions that denote merely calendar date time periods are classified under the category of Calendar Date Expressions Denoting Time Periods. Expressions that belong to this category are those time expressions that explicitly denote a time interval in a given calendar such as calendar days, calendar weeks, months, hours. In our regard, these expressions do not bear socio-cultural characteristics, in other words they are independent of socio-cultural contexts. Examples of such expressions are “12.6.2004”, “January”, “12.00 p.m.”, “8.00 a.m.”, etc. Category Calendar Date Expressions Denoting Time Periods underlines the distinction between socio-cultural time expressions and regular time expressions.

 

Remaining time expressions denoting time periods do bear socio-cultural characteristics, therefore they qualify as expressions denoting socio-cultural time periods. These comprise the second category that is the Socio-Cultural Time Expressions Denoting Time Periods. The two categories constitute the third level of the hierarchy and they are at the same level. We refer to the categories that are at the same level as co-ordinate categories. Hence, category of Calendar Date Expressions Denoting Time Periods and Socio-Cultural Time Expressions Denoting Time Periods are co-ordinate categories.

 

Categories are declared as subcategories, supercategories or co-ordinate categories with respect to their relations to each other in the hierarchy. A subcategory has all the characteristics of its supercategory and at least one further characteristic, which distinguishes it from its co-ordinate categories. Thus, both categories of Calendar Date Expressions Denoting Time Periods and Socio-Cultural Time Expressions Denoting Time Periods extend the category of Time Expressions Denoting Time Periods with further characteristics and they are distinct. Time expressions that belong to the category of Calendar Date Expressions Denoting Time Periods are necessarily expressions denoting time periods, additionally they are denoting explicit time periods. For example, “Bed Time”, “Tomorrow”, “Last Month” cannot be instances of the category Calendar Date Expressions Denoting Time Periods because they do not denote concepts of time periods that are explicit. Concept Bed Time can be, as a matter of fact, any time in the evening or even during the day. In order to determine the time concept of Tomorrow or Last Month current day and current month need to be known.

 

Time expressions that belong to the category of Socio-Cultural Time Expressions Denoting Time Periods are necessarily time expressions denoting time periods and they have additionally socio-cultural characteristics. For example, “Columbus Day” is a time expression denoting a time period of one day and it is an expression used in the USA. Likewise, “Yom Kippur” is an expression denoting a concept of a time period, which is also one day long. This expression is used in the Jewish religion and the Israeli nation.

 

Based on the general requirements mentioned afore, the two categories are two distinct types. Except for some special cases, which we will refer to soon, no time expression can be a member of both categories. An expression that belongs to the category Calendar Date Expressions Denoting Time Periods has type Calendar Date Expressions Denoting Time Periods, whereas an expression that belongs to the category Socio-Cultural Time Expressions Denoting Time Periods has type Socio-Cultural Time Expressions Denoting Time Periods. The two expressions are two unique expressions that have different types.

 

The category Calendar Date Expressions Denoting Time Periods is not broken down into any further categories, whereas the category of Socio-Cultural Time Expressions Denoting Time Periods is. Two questions have to be answered at the category of Socio-Cultural Time Expressions Denoting Periods to obtain further subcategories. These questions are “how long?” and “from where?” The first question targets at extracting information about the duration of the time period that the expression denotes and the second question targets at extracting the origin of the time period that the expression denotes. Thus, first question reveals the temporal dimension of Socio-Cultural Time Expressions Denoting Time Periods and the second question reveals the socio-cultural dimension. Once again, with these questions we are referring to the meaning of the questions as this is necessary to determine the categories.

 

Consequently, further subcategories of the category Socio-Cultural Time Expressions Denoting Time Periods emerge. These are Socio-Cultural Time Expressions Denoting Time Periods Related to Nations, …Related to Religions, … Related to Business Life & Education, Socio-Cultural Time Expressions Denoting Time Periods with Duration of One Day, …with Duration of Longer than One Day and finally …with Duration of Shorter than One Day, which are each other’s co-ordinate categories.

 

The majority of socio-cultural time expressions have been assigned to appropriate categories on the basis of these criteria. However, as we have mentioned previously, some expressions such as the expression “Holiday” and the expression “Sabbath” are vague in meaning, i.e. they denote multiple concepts, therefore they belong to multiple categories w.r.t. the classification criteria. Hence, these expressions have not been assigned to a single category but to multiple categories. For example, the expression “Holiday” has been assigned to both the category Socio-Cultural Time Expressions Denoting Time Periods with Duration of One Day and to Socio-Cultural Time Expressions Denoting Time Periods with Duration of Longer than One Day because the use of this expression in the natural language denotes both a period of one day and a period that is longer than one day. In the Ontology of Socio-Cultural Time Concepts, however, the time concept Holiday is modelled as a socio-cultural time period with duration of one day. In other words, the time concept Holiday is the member of only the category Socio-Cultural Time Periods with Duration of One Day.

 

As a result of the ambiguity of socio-cultural time expressions, there are several other cases, where one expression is assigned to multiple categories in the Ontology of Socio-Cultural Time Expressions. In the Ontology of Socio-Cultural Time Concepts, these multiple assignments are reduced to single assignments and the associated concepts are marked in a special way to indicate the exceptional situation. We will refer back to this issue one more time in the Ontology of Socio-Cultural Time Concepts. Here is a depiction of the top level category and some high-level categories of the classification hierarchy:

 

 

Clearly, the classification criteria can be extended to include finer categories. For example, a category Socio-Cultural Time Expressions Denoting Time Periods of One Week could be defined, which would then include expressions such as “Holy Week”, “Passion Week” and so forth. Further categories, can be defined to include expressions denoting time periods of half a day, afternoons, between 12.00 and 13.00 (e.g. “Lunch Time”) and so forth. Similarly, Socio-Cultural Time Expressions Denoting Time Periods can be extended to include categories such as Socio-Cultural Time Expressions Denoting Time Periods Related to Sports (e.g. “Training Hours”, “Camp Days”, “Time Out”), …Related to Healthcare (e.g. “Surgery Hours”, “Consultation Hours”), …Related to History (e.g. “Renaissance, Victorian Era”).

 

At this time, we arrive at the fourth level of the classification hierarchy and we start to combine the co-ordinate categories in an exhaustive manner so that in the end every possible combination has been realized. More precisely, we combine the categories Socio-Cultural Time Expressions Denoting a Time Period of One Day, …Longer than One Day and …Shorter than One Day with the categories of Socio-Cultural Time Expressions Denoting Time Periods Related to Nations, … Related to Religions and …Related to Business Life & Education. As a result, we obtain combination (or intersection) categories such as Socio-Cultural Time Expressions of Nations Denoting a Time Period of One Day, Socio-Cultural Time Expressions of Religions Denoting a Time Period of Longer than One Day, and so forth. These categories constitute the fifth level of the hierarchy.

 

Based on the reasons that have been provided before, particular attention is paid to the nations USA, Turkey, Germany, Israel, to the religions Islam, Christianity, Judaism and to the social groups involving business people and members of secondary and higher education. Therefore, categories concerning the relevant religions, nations and social groups have been defined and they have been subordinated to one of the appropriate combinatory categories defined above. For example, the category of Turkish Time Expressions Denoting Time Periods with Duration of One Day is subordinated to the category of Socio-Cultural Time Expressions Related to Nations Denoting Time Periods with Duration of One Day and the category of Socio-Cultural Time Expressions Related to Higher Education Denoting Time Periods with Duration of Longer than One Day is subordinated to the category of Socio-Cultural Time Expressions Related to Business Life and Education Denoting Time Periods with Duration of Longer than One Day. Here is another depiction of the fourth, fifth and sixth levels of the classification hierarchy that shows a combination category and its subcategory:

  

 

 

All four nations, three religions and three social groups are categorised in this manner. Note the graph structure of the classification hierarchy. Within the general design requirements, we have specified that it is desired to be able to find an instance starting out from different points in the hierarchy. Considering the depiction above, it would be possible to find an instance assigned to the category of US American Time Expressions Denoting a Time Period of One Day both starting out from the category Socio-Cultural Time Expressions Denoting Time Periods of One Day and from category Socio-Cultural Time Expressions Denoting Time Periods Related to Nations.

 

Clearly, it is possible to extend the classification hierarchy at the sixth level to include further nations, religions and social groups. Lowest level categories of the classification hierarchy include categories such as Israeli-Jewish Time Expressions Denoting a Time Period of One Day or Turkish-Islamic Time Expressions Denoting a Time Period of One Day, etc. These categories were necessary because in our collection some expressions are of both Islamic and Turkish origin. Similarly, some expressions are of both Jewish and Israeli origin. Since an expression is not allowed to be the instance of more than one category (except for the special cases), we have defined the above mentioned combination categories.

 

Instances of the Ontology of Socio-Cultural Time Expressions Related to Nations, Religions, Business Life & Education are the expressions of socio-cultural time denoting time periods. For example, the expressions “St. Patrick’s Day”, “Academic Trimester” or “Day of Repentance and Prayer” constitute the instances of the ontology. Every instance is assigned to an appropriate category and in cases of ambiguity to multiple categories. For example, the expression “St. Patrick’s Day” is an instance of the category Christian Time Expressions Denoting Time Periods of One Day and the expression “Academic Trimester” is an instance of the category Socio-Cultural Time Expressions Related to Higher Education Denoting Time Periods with Duration of Longer than One Day.

 

Some categories do not have direct instances. That is, some categories have instances in terms of the instances of their subcategories. The category Socio-Cultural Time Expressions Denoting Time Periods constitutes such a case. It does not have direct instances itself but its subcategories do. For example, the expression “St. Patrick’s Day” above, which is a direct instance of the category Christian Time Expressions Denoting Time Periods with Duration of One Day, is at the same time an indirect instance of the category Socio-Cultural Time Expressions Denoting Time Periods because the former category is a subcategory of the latter.

 

So far, we have examined the categories and the instances of the Ontology of Socio-Cultural Time Expressions. Before we proceed to the issues, where the current ontology differs from the Ontology of Socio-Cultural Time Concepts, we inspect the properties (or attributes) of the ontology.

 

There are five different types of properties defined in the ontology. These properties are, denotes Time Period of Fixed Date, denotes Time Period of Variable Date, denotes Time Period of General Suspension of Classes, denotes Time Period of General Suspension of Work. As such, the properties comprise the characteristics of a category. Every expression that is an instance of the category will automatically carry the characteristics i.e. the properties of that category. Properties in the Ontology of Socio-Cultural Time Expressions are defined only at the category Socio-Cultural Time Expressions Denoting Time Periods because we are particularly interested in defining the characteristics of the expressions of socio-cultural time. All the subcategories of the category Socio-Cultural Time Expressions Denoting Time Periods carry the characteristics of their supercategory. In other words, they inherit the properties.

 

This means that all expressions that are assigned to the category Socio-Cultural Time Expressions Denoting Time Periods or to one of its subcategories will be furnished with these properties. Put another way, the instances will carry all the characteristics of the category they belong to, which distinguish them from the instances of other categories. So, let us explain the meaning and the function of the properties.

 

1.      denotes Time Period of Fixed Date property is defined at the category of Socio-Cultural Time Expressions Denoting Time Periods, which is at the same time the subject value of the property. The object value is a boolean, hence the property is a binary relation between the an instance of the ontology that is a member of the category Socio-Cultural Time Expressions Denoting Time Periods and a boolean, which is a member of the category Literal. The category Literal does not show up in the actual classification hierarchy and it can be considered as a system class that functions as a container for all kinds of literal values such as strings, integers, booleans and so forth defined in the ontology. The property is of the form:

 

 

Table 2

Subject value and the object value of the property denotes Time Period of Fixed Date

 

Thus, each socio-cultural time expression that is an instance of the category Socio-Cultural Time Expressions Denoting Time Periods or an instance of one of its subcategories carries the property denotes Time Period with Fixed Date that can be either TRUE or FALSE. So, each expression reports whether or not it refers to a period of time whose date is fixed. For example, if we define the expression “St. Valentine’s Day” to be the instance of the category Christian Time Expressions Denoting Time Periods with Duration of One Day, then it will be necessarily equipped with the property denotes Time Period of Fixed Date. Thus, it will be related to a boolean value that can be either TRUE or FALSE. St. Valentine’s Day happens on 14^th of February each year, so we can state the following: “St. Valentine’s Day” denotes Time Period of Fixed Date TRUE. We can translate this statement as “St. Valentine’s Day is a socio-cultural time expression that denotes a time period of a day with a fixed date on the timeline”. The purpose of this attribute is to demonstrate the socio-cultural time expressions that denote periods of time, which can always be anchored on the same fraction of the timeline.

 

2.      denotes Time Period of Variable Date property is defined at the category of Socio-Cultural Time Expressions Denoting Time Periods, which is the subject value of the property. The object value is a boolean, hence the property is a binary relation between an instance of the ontology that is a member of the category Socio-Cultural Time Expressions Denoting Time Periods and a boolean value, which is a member of the category Literal. It is of the form:

 

 

Table 3

Subject value and the object value of the property denotes Time Period of Variable Date

 

 

Thus, each socio-cultural time expression that is an instance of the category Socio-Cultural Time Expressions Denoting Time Periods or an instance of one of its subcategories carries the property denotes Time Period of Variable Date that can either be TRUE or FALSE. So, each expression reports whether or not it refers to a period of time whose date is variable. For example, if we define the expression “Easter Monday” to be the instance of the category Christian Time Expressions Denoting Time Periods with Duration of One Day, then it will necessarily carry the property denotes Time Period of Variable Date. Thus, it will be related to a boolean value that can be either TRUE or FALSE. Easter Monday happens on a different date each year, so we can state for the following: “Easter Monday” denotes Time Period of Variable Date TRUE, which we can be translated as “Easter Monday is a socio-cultural time expression that denotes a time period that is a day long with a variable date on the timeline”. The purpose of this attribute is to demonstrate the socio-cultural time expressions that denote periods of time, which cannot be anchored on the same fraction of the timeline.

 

3.      denotes Time Period of General Suspension of Classes property is defined at the category of Socio-Cultural Time Expressions Denoting Time Periods, which is the subject value of the property. The object value is a boolean, hence the property is a binary relation between an instance of the ontology that is a member of the category Socio-Cultural Time Expressions Denoting Time Periods and a boolean value, which is a member of the category Literal. It is of the form:

 

 

Table 4

Subject value and the object value of the property denotes Time Periods of General Suspension of Classes

 

Thus, each socio-cultural time expression that is an instance of the category Socio-Cultural Time Expressions Denoting Time Periods or an instance of one of its subcategories will carry the attribute denotes Time Period of General Suspension of Classes that can be either TRUE or FALSE. So, each expression reports whether or not it refers to a period of time that is associated with a change in the usual flow of education life (i.e. periods of time when there is no teaching and no classes are held). For example, if we define the expression “Semester Break” to be the instance of the category Socio-Cultural Time Expressions Denoting Time Periods Related to Higher Education with Duration of Longer than One Day, then it will necessarily carry the attribute denotes Time Period of General Suspension of Classes and will be related to a boolean value that can be either TRUE or FALSE. During Semester Break no classes are held at a university so we can state the following:

 

“Semester Break” denotes Time Period of General Suspension of Classes TRUE, which can be translated as “Semester Break is a socio-cultural time expression that denotes a time period longer than a day, when no classes in higher education are held”.

 

4.      denotes Time Period of General Suspension of Work property is defined at the category of Socio-Cultural Time Expressions Denoting Time Periods, which is the subject value of the property. The object value is a boolean, hence the property is a binary relation between an instance of the ontology that is a member of the category Socio-Cultural Time Expressions Denoting Time Periods and a boolean value, which is a member of the category Literal. It is of the form:

 

 

Table 5

Subject value and the object value of the property denotes Time Period of General Suspension of Work

 

Hence, each socio-cultural time expression that is an instance of the category Socio-Cultural Time Expressions Denoting Time Periods or an instance of one its subcategories carries the property denotes Time Period of General Suspension of Work that can be either TRUE or FALSE. So, each expression reports whether or not it refers to a period of time that is associated with a change in the usual flow of business life (i.e. periods of time when business are officially closed, no mail is delivered and there is no trade) For example, during the time period St. Patrick’s Day there is no general suspension of work and the business carries on same as on the regular days so we can state the following: “St. Patrick’s Day” denotes Time Period of General Suspension of Classes FALSE. We can translate this as “St. Patrick’s Day is a socio-cultural time expression that does not denote a period of time, when work and official businesses are suspended based on the determination of a legal authority”.

 

As we have discussed in the previous chapter, the properties above disclose how the expressions of socio-cultural time deliver information about the underlying conceptual structure. Thus, the properties refer to the meaning of the expressions, however the meaning is not determined in an explicit and unambiguous manner. This will be done in the next ontology that models the concepts. If the information delivered by these properties is formally and unambiguously described in the ontology at the conceptual level, i.e. in the Ontology of Socio-Cultural Time Concepts, then this kind of information can facilitate reasoning, for example, for appointment scheduling processes. On the basis of this information, a reasoning mechanism can conclude whether or not a given period of time is official working time, or teaching time. It can infer whether or not a specific time period of a given year will correspond to the same time fraction also next year and in the following years. To underline one more time, these properties only deliver information to the ontology at the conceptual level, therefore the reasoner can only refer to the ontology at the conceptual level that makes use of this information and redefines it in an unambiguous manner.

 

There are similarities and differences between the Ontology of Socio-Cultural Time Expressions and the Ontology of Socio-Cultural Time Concepts. As it has been mentioned several times, the former ontology assigns the expressions of socio-cultural time that are a subset of natural language expressions to appropriate categories, which are organized in a hierarchical order w.r.t. subclass-superclass relationship. The latter on the other hand, assigns the concepts of socio-cultural time that are denoted by the expressions to appropriate categories, which are organized in a hierarchical order. As such, the first ontology does not attempt to describe the meaning of the expressions in an unambiguous manner, whereas the second does.

 

The distinction between the two ontologies can be observed by looking at the definition of the categories and properties of the Ontology of Socio-Cultural Time Expressions. Category names such as Socio-Cultural Time Expressions Denoting Time Periods or Socio-Cultural Time Expressions Denoting Time Periods Related to Religions point out to the fact that the expressions only denote the associated concepts and even though they refer to the meaning, they do not provide a clarification of the meaning. As a result of the ambiguity of the expressions, there are cases in the Ontology of Socio-Cultural Time Expressions, where one instance (expression) is assigned to multiple categories, whereas in the second ontology this is strictly avoided. Furthermore, in the Ontology of Socio-Cultural Time Expressions, there are no properties such as has Similar Meaning, has Subordinate Concept, or has Superordinate Concept that relate the categories to each other because they refer to the meaning of the expressions; in other words they refer to the concepts. Out of same reasons, properties such as has Duration, has Granularity and so forth are not defined at any category in the Ontology of Socio-Cultural Time Expressions. Consequently, such properties are defined either in the Ontology of Socio-Cultural Time Concepts as that is the ontology, which attempts to provide an unambiguous explication of the meaning of the expressions of socio-cultural time. This issue will be discussed in detail in the forthcoming sections.

 

Instances of the ontology are the expressions of socio-cultural time related to nations, religions, business life & education. As such, the instances are to be understood as representations of different lexical forms of talking about socio-cultural time. Some examples of instances are expressions such as “Martin Luther King’s Birthday”, “Academic Year”, “Good Friday” and so forth. Each instance has the type of the category it belongs to. For example, “Martin Luther King’s Birthday” is an expression, which denotes a time period of one day and which is used to talk about the specific day (every third Monday of every January) in the USA that is reserved to celebrate the birthday of the assassinated civil rights fighter Reverend Dr. Martin Luther King. Based on this information, the expression is assigned to the category US American Time Expressions Denoting Time Periods of One Day so now it has the type US American Time Expressions Denoting Time Periods of One Day. In a similar way, the expression “Academic Year” is an instance of the category Socio-Cultural Time Expressions Related to Higher Education Denoting a Time Period of Longer than One Day and the expression “Good Friday” is an instance of the category Christian Time Expressions Denoting a Period of One Day.

 

In order to provide an explicit and precise definition of the socio-cultural time and eventually to be able to provide support to automated temporal Web application systems, we refer to the concepts that the expressions denote. For each expression, we determine the concept, which is most relevant to the domain and include only that concept in the Ontology of Socio-Cultural Time Concepts as the denotation of the associated socio-cultural time expression. Thus, each socio-cultural time expression has one associated socio-cultural time concept in the Ontology of Socio-Cultural Time Concepts, which can be understood as the meaning of the expression.

 

As we have mentioned, the expression “Holiday” is assigned to two different categories because of its ambiguous nature. Thus, it is both an instance of the category Socio-Cultural Time Expressions Denoting a Time Period of One Day and an instance of the category Socio-Cultural Time Expressions Denoting a Time Period of Longer than One Day in the Ontology of Socio-Cultural Time Expressions. Its associated concept Holiday, however, is only assigned to the category of Socio-Cultural Time Periods with Duration of One Day in the Ontology of Socio-Cultural Time Concepts. Hence, we have determined one socio-cultural time concept as the only interpretation of the expression “Holiday” in the Ontology of Socio-Cultural Time Concepts. We will come back to this case one more time in the next subsection.

 

We conclude this subsection with the following two figures that show the subclass and instanceOf relationships of the classification hierarchy and the multiple assignment of the expression “Holiday” as an instance of the both categories Socio-Cultural Time Expressions Denoting a Time Period of One Day and Socio-Cultural Time Expressions Denoting a Time Period of Longer than One Day:

 

 In this section, we have explained the role of the Ontology of Socio-Cultural Time Expressions within the context of this thesis. We have stated that socio-cultural time expressions deliver information about the underlying conceptual structure of socio-cultural time and we have mentioned that as a result of this fact Ontology of Socio-Cultural Time Expressions has been designed. We have also mentioned that the Ontology of Socio-Cultural Time Expressions alone falls short to provide a precise and explicit description of the domain of socio-cultural time related to nations, religions, business life & education because of the ambiguous nature of the expressions of socio-cultural time. We have demonstrated and discussed examples about the complexities that have arisen as a result of this fact. Thus, we have pointed out to the necessity of a model at the conceptual level and justified the need for the Ontology of Socio-Cultural Time Concepts. We have presented some categories, some instances and the attributes defined in the Ontology of Socio-Cultural Time Expressions and demonstrated some classification hierarchies. Finally, we have provided a brief comparison of the current ontology and the Ontology of Socio-Cultural Time Concepts.  

5.2	Purpose and Scope of the Ontology of Socio-Cultural Time
	Concepts Related to Nations, Religions, Business Life & Education

 

In this section we will examine the purpose and the scope of the Ontology of Socio-Cultural Time Concepts in detail. We have already clarified the need for such a conceptual level to provide a description of the domain socio-cultural time related to nations, religions business life & education in a precise and unambiguous manner. This section will demonstrate, how the Ontology of Socio-Cultural Time Concepts supplies this need. Thereby, an overview of the categories, the attributes, the relations and the instances of the ontology will be provided. The similarities and the differences between the Ontology of Socio-Cultural Time Concepts and Ontology of Socio-Cultural Time Expressions will be recapitulated.

 

General requirements concerning the design that have been defined and explained previously, apply to the Ontology of Socio-Cultural Time Concepts. To recall, these requirements are typing, category combination, stability, extensibility and graph structure. At the end of this subsection, we will generate an Ontology Specification Document for the Ontology of Socio-Cultural Time Concepts, according to the METHONTOLOGY. This document will present the Ontology of Socio-Cultural Time Concepts in a nutshell.

 

As we have pointed out many times, a precise, unambiguous and systematic description is essential if our goal is to support temporal Web application systems by acquainting them with a different notion of time i.e. the notion of socio-cultural time. This way, they can become more (socio-cultural) context sensitive and they can better react against the context specific needs and preferences of their users. Let us recall the argument briefly why this kind of support is necessary and describe the path that lead to the development of the Ontology of Socio-Cultural Time Concepts.

 

Today, as a result of the modern technology, the interaction between people from different socio-cultural contexts is very high. However, different people may have different conceptions about the real world and a reason for this is the different socio-cultural contexts that the people belong to. Often, when members of different socio-cultural groups interact with each other they take their own conception of the world as a benchmark. So, they fail to recognize the fact that each member, depending on the socio-cultural context, may have a different conception about a common issue. As a result, communication problems arise. As we have seen previously, same is the case for the conception of time.

 

There is a conception of time that exists independently of the absolute conception of time given in natural science and that is entirely dependent on cultures and social groups. However, this conception of time is implicitly present in people’s minds and in most cases members of one socio-cultural group assume that members of the other socio-cultural group would share the same conception of time with them. Like in the previous Summer Semester example, the members of Turkish culture may assume that there is no Summer Semester in German academic system because there is none in Turkish academic system or the opposite way around. Such false assumptions and the consequent communication problems could be avoided, if the implicit conceptions of time are made explicit and shared with others.

 

Within the scope of this thesis, we assume that the socio-cultural context dependent conception of time is also present on the Web and it plays a role during the interaction on the Web. Therefore, we defend the idea that an explicit description of socio-cultural time is essential for the Web. Today, billions of people from different countries, cultures and social groups are connected to Web and they continuously interact with each other. Moreover, people from different social-contexts develop software applications to be used on the Web that are tailored for their context dependent needs and expectations. Quite often, it is the case that such software applications interact with each other on the Web in order to accomplish common tasks. Yet, these interactions involve a socio-cultural context specific conception of time that has not been explicitly defined. Therefore, we believe in the necessity of the explicating socio-cultural context dependent conception of time to be able to avoid possible communication problems between people and between software applications on the Web. Once this conception of time is defined in an explicit, systematic and machine processable way, it can be used to support temporal Web application systems so that they can react in a more sensitive way to the users’ culture specific needs.

 

 

Starting out with this motivation, we have defined our task to provide a formal, explicit, unambiguous and systematic description of knowledge about socio-cultural time related to nations, religions and business life and education for the Web to support temporal Web application systems such as automated appointment schedulers. We believe appointment scheduling is a task, where different conceptions of time can be observed frequently and where they play an important role.

 

Acknowledging that the expressions of natural language deliver information about the conceptual structure of the real world, we have turned our attention to the expressions of socio-cultural time. Thus, as a first step we have developed the Ontology of Socio-Cultural Time Expressions. However, we have observed that socio-cultural time expressions cannot provide us with the essential conceptual explicitness, precision and systematics due to the ambiguous nature of the expressions. To achieve this, a conceptual level is needed, where the meaning of socio-cultural time expressions is unambiguously described. So, we have developed the Ontology of Socio-Cultural Time Concepts to be able to accomplish our task. In brief, we have partitioned the domain socio-cultural time related to nations, religions and business life & education into two. The first partition is a collection of time expressions of natural language related to the specific Socio-Cultural groups mentioned above, which we call “socio-cultural time expressions”. The second partition of the domain corresponds to a collection of concepts of socio-cultural time periods denoted by these socio-cultural time expressions.

 

As such, the Ontology of Socio-Cultural Time Concepts is a model of the concepts denoted by the expressions in the Ontology of Socio-Cultural Time Expressions. Therefore, to a large extent, the structure of the first ontology corresponds to the structure of the second ontology. Yet, there are also significant differences.

 

The major point, where the two ontologies part from each other is the meaning. The Ontology of Socio-Cultural Time Concepts models the concepts of socio-cultural time, whereas the Ontology of Socio-Cultural Time Expressions models the expressions of socio-cultural time. More precisely, the subject of the former is the concepts and the subject of the latter is the expressions. As a result, in the Ontology of Socio-Cultural Time Expressions, some instances may belong to several categories at the same time to demonstrate the ambiguity of the expressions. In the Ontology of Socio-Cultural Time Concepts this is not possible. In our collection of socio-cultural time expressions, each expression necessarily denotes a concept of time period. Therefore, categories of the Ontology of Socio-Cultural Time Concepts are categories of time periods (whereas the categories of the other ontology are categories of time expressions denoting time periods).

 

 We have discussed thoroughly that socio-cultural time expressions are often vague in meaning. Frequently, one socio-cultural time expression denotes several socio-cultural time concepts, in our case socio-cultural time periods. The expressions of “Holiday” and “Sabbath” are some examples. We have also stated that in order to be able to avoid the ambiguity and to provide precise meaning and consensus about the domain, a decision needs to be taken concerning the meaning of the expressions. More precisely, one concept and only one concept should be determined as the denotation of the expression at hand and only this concept should be included in the model. This would amount to allowing only one possible interpretation for a socio-cultural time expression by reducing the relationship between the expression and the concepts it denotes from one-to-many to one-to-one. This practice is similar to saying that a given expression has exactly one meaning and only that meaning. Once we have decided on one meaning, it can be precisely described and consensus can be achieved if this description would be shared and accepted by others. So, Ontology of Socio-Cultural Time Concepts has the purpose of explicating the meaning of socio-cultural time (related to nations, religions and business life & education) without ambiguity and providing consensus about the domain.

 

Consequently, each concept of socio-cultural time is classified only under one category (unlike the case in the former ontology). Referring back to example with the expression “Holiday”, in the Ontology of Socio-Cultural Time Concepts the socio-cultural time concept Holiday is defined as “any day that is 24 hours long and that is associated with a special religious observance, or a national celebration, or with a celebration related to a social group, which in some cases indicates a general suspension of work or classes”. This is the one and the only definition present in the Ontology of Socio-Cultural Time Concepts. In other words, this is the one and the only interpretation of the socio-cultural time expression “Holiday” that can be found in our conceptual model for the domain of socio-cultural time related to nations, religions and business life & education. In the documentation of Ontology of Socio-Cultural Time Concepts such concepts are marked with a sign “Ó” to indicate that they have been standardized. In other words, concepts such as the concept Holiday or the concept Sabbath in our model carry such a sign to inform that in the natural language their associated expressions denote also other socio-cultural time concepts. Accordingly, in the Ontology of Socio-Cultural Time Concepts the concept Holiday and the concept Vacation for example are treated as two distinct concepts. In the next subsection such socio-cultural time concepts are referred to in detail.

 

There is an additional aspect that the Ontology of Socio-Cultural Time Concepts considers, which involves the possibility of linking up the ontology with a temporal type system. Let us explain this. We have mentioned the purpose of the ontology several times; provide a precise and systematic description of the socio-cultural time related to nations, religions and business life & education to support temporal Web application systems such as automated appointment schedulers so that they can react more sensitively to the context specific needs of their users. If we reconsider this purpose, we can see that with the ontology we are not targeting at providing yet another formal description of temporal information. Instead, we want to provide additional information, in our case socio-cultural temporal information, to the existing formal temporal information. Moreover, we do not aim to conduct calendrical calculations for the time periods defined in the ontology. We assume that temporal systems exist that pin down the socio-cultural temporal information being described in the ontology to the desired calendar system. An example of such a temporal type system is Multi-Calendar Temporal Type System for (Semantic) Web Query Languages [80]. The system will enable the definition of regular time concepts such as hour and day as well as the definition of socio-cultural time concepts like Teaching Term and Christmas Day for Web query languages.

 

In order to facilitate a seamless integration with such a temporal type system, the socio-cultural time ontology needs to provide ways to relate socio-cultural temporal information to regular temporal information. This can be done by explicating the regular temporal information embedded in the socio-cultural temporal information. Therefore, in the Ontology of Socio-Cultural Time Concepts each entry of socio-cultural time concept delivers also regular temporal information. More concretely, each instance of socio-cultural time concept like the Thanksgiving Day, Sabbath, Semester is furnished with several properties such as has Duration, has Granularity, has Index and so forth, that deliver regular temporal information about that particular instance of socio-cultural time concept. Similar as in the previous ontology, the properties are defined at the category of Socio-Cultural Time Periods, thus each instance of this category or one of its subcategories carries these properties. Next subsection will explain the meaning and the function of the properties in detail.

 

Instances of the Ontology of Socio-Cultural Time Concepts are the concepts of socio-cultural time that are in our model necessarily instances of time periods. Recall that the instances of the Ontology Socio-Cultural Time Expressions are the instances of natural language expressions of socio-cultural time. As such, socio-cultural concepts of time, which are time periods, represent the different concepts of socio-cultural time. For example, instances such as Martin Luther King’s Birthday, Academic Year and Good Friday are instances of socio-cultural time periods, in other words they have the type socio-cultural time period. Accordingly, the time concept Martin Luther King’s Birthday is an instance of US American Time Periods with Duration One Day. The time concept Academic Year is an instance of the category Socio-Cultural Time Periods Related to Higher Education with Duration of Longer than One Day and the time concept Good Friday is an instance of the category Christian Time Periods with Duration One Day.

 

To conclude, we present the Ontology Specification Document for the Ontology of Socio-Cultural Time Concepts according to METHONTOLOGY.

 

 

This section has recalled the motivation behind the thesis and specified the purpose and the scope of the Ontology of Socio-Cultural Time Concepts. It has informed that the current ontology corresponds to the conceptual level of the domain and that it covers the meaning of the expressions modelled in the Ontology of Socio-Cultural Time Expressions. The reasons for the necessity of Ontology of Socio-Cultural Time Concepts have been explained as well. The subsection has also given an overview about the contents of the ontology. A comparison of the current ontology with the Ontology of Socio-Cultural Time Expressions has also been made and the similarities and differences between them have been discussed. More precisely, the purpose of the first ontology is to deliver information about the concepts of socio-cultural time and to justify the need for the Ontology of Socio-Cultural Time Concepts. The purpose of the second ontology is to explicate the meaning of the expressions of socio-cultural time, in other words to describe the concepts of socio-cultural time in an unambiguous and precise manner to provide consensus. Therefore, in cases, where a socio-cultural time expression denotes several time concepts (thereby belongs to multiple categories), only one concept has been considered and described in the Ontology of Socio-Cultural Time Concepts, where the concept is marked with the sign ‘Ó’. In this subsection we have also explained that the Ontology of Socio-Cultural Time Concepts has the purpose to support temporal systems with additional temporal information (about nations, religions and business life & education), therefore the ontology should deliver the sufficient regular temporal information about each socio-cultural concept entry along with the socio-cultural information. Accordingly, we have stated that several attributes have been defined to fulfil this purpose. Finally, the Ontology Specification Document of the Ontology of Socio-Cultural Time Concepts has been generated w.r.t. the METHONTOLOGY.

 

5.3	Conceptualization of the Ontology of Socio-Cultural Time
	Concepts Related to Nations, Religions, Business Life & Education

 

This section is devoted to the conceptualization activity of the ontology, where the domain knowledge will be structured in conceptual models. According to METHONTOLOGY, the conceptualization activity describes the problem and its solution in terms of the domain vocabulary identified in the ontology specification activity. More precisely, in this section we will demonstrate how we used the elements of the ontology defined in the previous section to obtain the Ontology of Socio-Cultural Time Concepts as it is now.

 

Conceptualization activity is composed of several steps. First step is the definition of a Glossary of Terms, which is a list of everything that will show up in the ontology. In our case, it is a list of socio-cultural time periods related to nations, religions, business life & education and their associated characteristics.

Second step is the creation of a Concept Classification Hierarchy, where the concepts of socio-cultural time periods of the ontology are assigned to appropriate categories and are organized in hierarchical order w.r.t. subclass-superclass relations. We will demonstrate some instance relationships as well.

Third step of the conceptualization activity is the building of a Concept Dictionary, where detailed information about the categories of the ontology will be delivered. Such information will include for example the category name, its description, its properties, and so forth. Subsequently, a Binary Relations Table and Diagram will be presented that depicts the property relations in the ontology, which exist with the taxonomic relations simultaneously.

Last step of the conceptualization activity is the creation of Instances Table that gives information about the instances of the ontology along with their descriptions, associated categories, properties and property values.

 

In brief, this section will present a formal description of the Ontology of Socio-Cultural Time Concepts by defining and documenting the concepts, relations and instances related to the domain of socio-cultural time concepts related to nations, religions, business life & education.

 

5.3.1

Glossary of Terms

 

In this subsection, we will present a part of the Glossary of Terms for the Ontology of Socio-Cultural Time Concepts. As such, the glossary includes all categories, instances, properties that have been used in the ontology and it provides natural language descriptions for each one of them. Regarding the restricted space here we will present only some items defined in the glossary. Appendix A provides for the complete reference.

 

The purpose of the glossary is to determine the exact contents of the Ontology of Socio-Cultural Time Concepts, in other words to decide what the ontology should include and what not. At the same time, it displays a short description of the included items. In short, Glossary of Terms is thought as a quick reference to the contents of the ontology. Therefore, the definitions in the Glossary of Terms are not highly formal; instead they provide an idea about the general meaning or the function of the related item. An extract of the Glossary of Terms is presented in the following table. Left column of the table includes the name of the item, which can comprise a category, a property, or an instance (a concept of time period) and right column includes the associated semi-formal description.

 

 This subsection has provided a partial Glossary of Terms for the Ontology of Socio-Cultural Time Concepts. The purpose of the glossary is to provide a quick reference for the contents of the ontology by providing short, natural language descriptions of the items. The items or the terms of the glossary are the categories, relations, attributes and instances of the ontology. The descriptions are semi-formal. As such, the creation of the Glossary of Terms constitutes the first step of the conceptualization activity. The Classification Hierarchy, the Concept Dictionary and the Binary Relations Table and Diagram, which will be discussed in the next subsections will use the items defined in the Glossary of Terms.

 

5.3.2

Concept Classification Hierarchy

 

The Concept Classification Hierarchy comprises the focus of this subsection and it demonstrates the organization of the categories of the ontology in a hierarchical order w.r.t. subclass-superclass relations.

 

The classification criteria of the Ontology of Socio-Cultural Time Concepts are analogous to the previous ontology. The top level category is (┬). All other categories are subcategories of (┬). Top level category is divided into one subcategory; it is the category of Time Periods. This category represents concepts of all possible time periods such as calendar dates, days of weeks, months, and so forth, which can be explicitly anchored on the time line. All other concepts of time periods are not within the scope of the ontology.

 

Subcategories of one category are at the same level and they have the same criterion of subdivision. To determine the criterion we ask the question at the category Time Periods “Is the time period merely a calendar date time period, or is it a time period that is related to one of the socio-cultural groups specified within the scope of the ontology?” Time periods that bear no socio-cultural characteristics, in other words that are not related to specific a nation, to a religion or to a specific socio-cultural group, are classified under the category of Calendar Date Periods. Remaining time periods do bear socio-cultural characteristics and they qualify as socio-cultural time periods. These comprise the second category, which is the Socio-Cultural Time Periods. The two categories constitute the third level of the hierarchy and they are at the same level. Hence, Calendar Date Periods and Socio-Cultural Time Periods are co-ordinate categories.

 

Categories are declared as subcategories, supercategories or coordinate categories with respect to their relations to each other in the hierarchy. A subcategory has all the characteristics of its supercategory and at least one further characteristic, which distinguishes it from its co-ordinate categories. Thus, both categories Calendar Date Periods and Socio-Cultural Time Periods extend the category Time Periods with further characteristics. Time concepts that belong to the category Calendar Date Periods are necessarily time periods, which are additionally explicit. For example, Lunch-Time, Tomorrow, Last Month cannot be instances of the category Calendar Date Periods because they are not explicit. Lunch-Time does not necessarily have to be 12.00 p.m. In order to determine Tomorrow or Last Month, current day and current month need to be known. In contrast to this, March, Wednesday or 06-05-1976 can be instances of this category because they are explicit. March is always the third month of the year, Wednesday is always the third day of the week and 06-05-1976 is exactly the sixth day of the fifth month of the year 1976 (all w.r.t. Gregorian calendar).

 

Time concepts that belong to the category Socio-Cultural Time Periods are necessarily time periods and they have additionally socio-cultural characteristics. For example, Columbus Day is a time period of one day and it is a US American time concept. Likewise, Yom Kippur is a concept of a time period, which is also one day long and that is related to Jewish religion and Israeli nation.

 

The category Calendar Date Periods is not broken down into any further categories, whereas the category Socio-Cultural Time Periods is. Two questions are asked at the category Socio-Cultural Time Periods to obtain further subcategories. These questions are “how long?” and “from where?” The first question targets at extracting information about the duration of the time period and the second question targets at extracting the origin of the time period. Thus, first question depicts the temporal dimension Socio-Cultural Time Periods and the second question depicts the socio-cultural dimension.

 

Consequently, further subcategories of the category Socio-Cultural Time Periods emerge. These are, Socio-Cultural Time Periods Related to Nations, …Related to Religions, …Related to Business Life & Education, …Socio-Cultural Time Periods with Duration of One Day, …with Duration One of Longer than One Day and finally …with Duration of Shorter than One Day, which are co-ordinate categories.

 

At this time we arrive at the fourth level of the classification hierarchy and we start to combine the co-ordinate categories in an exhaustive manner. As a result, we obtain the subcategories, which are also co-ordinate categories of each other, such as Socio-Cultural Time Periods Related to Nations with Duration of One Day, …Related to Business Life and Education with Duration of Longer than One Day, and …Related to Religions with Duration of Longer than One Day. These constitute the fifth level of the hierarchy.

 

Based on the reasons that have been explained before, a particular attention is paid to the nations USA, Turkey, Germany, Israel, to the religions Islam, Christianity, Judaism and to the social groups involving business people and members of secondary and higher education. Therefore, categories concerning the relevant religions, nations and social groups have been defined and they have been subordinated to one of the appropriate combinatory categories defined above. For example, the category of Turkish Time Periods with Duration of One Day is subordinated to the category of Socio-Cultural Time Periods Related to Nations with Duration of One Day and the category of Socio-Cultural Time Periods Related to Higher Education with Duration of Longer than One Day is subordinated to the category of Socio-Cultural Time Periods Related to Business Life and Education with Duration of Longer than One Day. The top level and high levels of the classification hierarchy of the Ontology of Socio-Cultural Time Concepts can be represented as:

 

 

In the figure above, (┬) is the top level category, which is subdivided into the category of Time Periods. The category of Time Periods consists of the two subcategories Calendar Date Periods and Socio-Cultural Time Periods, which are determined on the basis of given characteristics. The former is not further subdivided, whereas the latter category is broken into further categories. The subcategories of Socio-Cultural Time Periods are presented on the fourth level of the hierarchy and they have emerged according to the dimensions of duration and socio-cultural origin.

 

Clearly, classification hierarchy can be extended at any level to include further categories. For example, the category Calendar Date Periods can be broken down to include finer categories such as Week Periods (e.g. the 2nd week of January), Yearly Quarters and Halves (e.g. the 4^th quarter) or Year Periods (e.g. the 60ies, 1920). Likewise, the category Socio-Cultural Time Periods can be extended to include finer categories such as Socio-Cultural Time Periods of One Week, …of Six Months  or Socio-Cultural Time Periods Related to Sports and so forth.

 

At the fourth level we start to combine categories of duration and categories of origin in an exhaustive manner so that in the end every possible combination has been realized. Thus, all co-ordinate categories at the fourth level are combined with each other in an exhaustive manner to yield the combination categories at the fifth level. Here are some examples of the combination of categories in the Ontology of Socio-Cultural Time Concepts:

 

 

 

Categories related to one specific religion, nation or social group like the Judaism, the Turkish nation or the social group of academia respectively comprise the sixth level of the hierarchy. Each category is subordinated to a relevant category at the fifth level. For example, Islamic Time Periods with Duration of One Day is subordinated to the category Socio-Cultural Time Periods Related to Religions with Duration of One Day; the category German Time Periods with Duration of Shorter than One Day is subordinated to the Socio-Cultural Time Periods Related to Nations with Duration of Shorter than One Day.

 

 

First section of the table above demonstrates the high level categories of the ontology classified according to the criteria duration and origin. Second and third sections show one of the high level categories of the ontology together with its subcategories, which are combination categories.

 

Additionally, above examples disclose the graph structure of the classification hierarchy. Due to the structure, it is possible to find an instance of the ontology that is a member of one category starting out from different points in the hierarchy. This aspect is also in accordance with the general design requirements specified for the ontology. Thus, an instance of the category Socio-Cultural Time Periods Related to Higher Education with Duration of One Day can be found either by entering the hierarchy from the category Socio-Cultural Time Periods with Duration of One Day or from category Socio-Cultural Time Periods Related to Business Life and Education.

 

In this subsection we have presented the hierarchical organization of the categories (taxonomy) in the Ontology of Socio-Cultural Time Concepts. We have pointed out to the identical structure of the current ontology with the Ontology of Socio-Cultural Time Expressions and mentioned the classification criteria. The process of combining categories to obtain new categories has also been explained and the graph structure of the classification hierarchy has been underlined. The instances of the categories have not been considered within this subsection, they will be the subject of the forthcoming subsections. Based on the classification hierarchies explained in the current subsection, next subsection will provide a formal description of the categories and will explicate their characteristics and the relations between them.

 

5.3.3

Concept Dictionary

 

In this subsection we will provide a formal description of the categories that have been presented in the classification hierarchy of the previous subsection. This process corresponds to the creation of the so-called Concept Dictionary according to METHONTOLOGY. Due to space restrictions, only a partial dictionary will be represented, whereby the complete reference can be found at the Appendix B. The formal description includes, for each category, a category name, a brief description of the category, the list of its attributes as well as the list of its associated instances for each category.

 

Table (9) below demonstrates an extract of the Concept Dictionary, which has been defined w.r.t. to the METHONTOLOGY. The leftmost column of the table is reserved for the names of the categories and it includes a number of high level categories of the ontology, which we have presented in the previous subsection. ‘Category Description’ is a formal, human readable description that gives information about the category. ‘Category Properties’ column lists the properties (attributes) that each category carries. ‘Category Instances’ column shows the instances that belong to each category.

The tables above demonstrate an extract of the categories of the Ontology of Socio-Cultural Time Concepts. Names of categories and their brief descriptions are provided. ‘Category Properties’ column presents the characteristics of the categories. These properties are defined at the category Socio-Cultural Time Periods at the second level of the hierarchy and are inherited to the lower categories of the hierarchy. Therefore, we have listed the attributes only one time at the category Socio-Cultural Time Periods.

 

Concepts of socio-cultural time periods are assigned to the categories of the ontology, so they represent the instances (individuals) of the Ontology of Socio-Cultural Time Concepts. Each category necessarily has instances either directly or indirectly. That is, if one category does not have direct instances, then it has instances through its subcategories. For example, in the Concept Dictionary above we can see that the category Socio-Cultural Time Periods is declared to have “no direct instances”. This does not imply that the category has no instances at all. Its subcategory Socio-Cultural Time Periods with Duration of One Day has a direct instance, which is the concept of Holiday©. Hence, the category Socio-Cultural Time Periods also has the instance Holiday©, however in an indirect way.

 

There is a reason why the socio-cultural time concept Holiday shows up with the special sign ‘©’. We have discussed previously that the concept of Holiday demonstrates a problematic case and it will be treated in a special manner. That is, only one meaning of the expression “Holiday” is referred to in the Ontology of Socio-Cultural Time Concepts. This is done by classifying the concept Holiday under the category Socio-Cultural Time Periods with Duration of One Day. The special sign ‘Ó’ is attached to the concept to indicate that in the natural language this concept is not the only one that is related to the expression “Holiday” but there are also others. For example, those defined in the Merriam Webster’s Dictionary that we have presented previously. Consequently, the Concept Dictionary presents the concept Holiday in form of Holiday©. Hence, the following holds for the time concepts in the Ontology of Socio-Cultural Time Concepts that come with the special sign ‘©’:

 

Note:

In the Ontology of Socio-Cultural Time Concepts, the special sign ‘Ó’ is attached to a time concept to indicate that in the natural language this concept is not the only one that is related to the expression (i.e. the associated expression is ambiguous). Hence, with the special sign, the meaning of the expression is standardized. In other words, only one interpretation is determined as the meaning of the expression among others. In the Ontology of Socio-Cultural Time Expressions, other associated expressions for the concept can be followed up.

 

 

Due to the ambiguous nature of the socio-cultural time expressions, there are more cases in the Ontology of Socio-Cultural Time Concepts, where the concepts of time periods are annotated this way. Let us list some of these cases. Appendix C provides for a full reference:

 

1.      Holiday©: In the Ontology of Socio-Cultural Time Concepts, the time concept of HolidayÓ is modelled as a time period that is one day long and that is associated with a special religious observance, or a national celebration, or with a celebration related to a social group, which in some cases indicates a general suspension of work or classes. In the natural language, the expression “Holiday” has various denotations. It may refer to a socio-cultural time period of one day (e.g. Thanksgiving) but it may also refer to a socio-cultural time period of longer than one day (e.g. summer holiday). Moreover, the time period holiday may be determined by a legal authority (e.g. Republic Day) but it may also be determined by the individual person (Vacation).

2.      May DayÓ and Labor DayÓ: May Day is celebrated on the 1^st of May in commemoration of the workers’ rights in most Europe and most other countries. Accordingly, in Germany May Day© is celebrated in this sense and is also referred as Labor Day. In the USA, on the other hand, May Day is celebrated on the 1^st of May to welcome the arrival of spring without having any connotation to the workers’ rights. Time concept of Labor Day© in the US American culture is independent of the time concept of May Day© and it is celebrated on the first Monday in September. It marks the end of summer holiday and the beginning of fall. In the natural language expressions “May Day” and “Labor Day” are used interchangeably. In the Ontology of Socio-Cultural Time Concepts May Day© is classified under the category German Time Periods with Duration One Day. Labor Day© is classified under the category US American Time Periods with Duration of One Day.

3.      SabbathÓ: In our model Sabbath© is considered as an Israeli-Jewish time period that has a duration of one day. In the natural language, the expression “Sabbath” can be used to imply a day reserved for free activities or a certain period of time, when one engages in work activities other than the regular work.

4.      Summer SchoolÓ: A school session conducted in summer enabling students to accelerate progress toward a degree, to make up credits lost through absence or failure, or to round out professional education. In the Ontology of Socio-Cultural Time Concepts, Summer School© is associated to higher education and it has duration of three weeks. In the natural language, however, the expression “Summer School” may be used to refer to a time period related to secondary education institutions, language courses or to other educational institutions and may apply various duration.

 

Finally, ‘Category of Relations’ column gives information about the subclass-superclass relationships between the categories. Accordingly, the category of Socio-Cultural Time Periods is the subcategory of the category Time Periods and at the same time it is the supercategory of the category Socio-Cultural Time Periods with Duration of One Day.

 

In this subsection we have formally described the categories that have been presented in the Classification Hierarchy of the previous subsection. In doing so, we have listed the taxonomic relations between the categories, the properties that hold for the categories and some examples of the instances of the categories. All this has been done by means of the Concept Dictionary w.r.t. METHONTOLOGY. Furthermore, we have mentioned the special treatment of some instances (that are concepts of time periods) in the ontology. We have given the partial list of these instances and explained the reasons why they have been treated this way.

 

5.3.4

Binary Relations Table and Diagram

 

In the Ontology of Socio-Cultural Time Concepts, there are several other relations besides the hierarchical relations that relate the categories to each other. In this subsection we will discuss these relations.

 

Binary relations are represented in form of properties or attributes and they relate one category to the other. Here, we use the term property to refer to these relations. If a category is linked to another category by a property, this means that every instance that belongs to the first category will be related to an instance that belongs to the second category along this property. We can also see this as one property relating a subject to its object.

 

There are two different kinds of properties. First kind of property relates a category in the hierarchy to another category in the hierarchy. Second kind of property relates a category in the hierarchy to another category that is present in the domain of the ontology but that does not show up in the hierarchy. That is the category Literals. As such, the category Literals hold all the string, integer and boolean values of the domain. Thus, the subjects of the second kind of property are instances of the categories in the hierarchy, whereas the objects of the property are arbitrary string, integer or boolean values.

 

Properties are inherited through the class hierarchy. Thus, every subcategory inherits the properties of its supercategory. Properties in the class hierarchy of the Ontology of Socio-Cultural Time Concepts are defined at the category of Socio-Cultural Time Periods. Consequently, all its subcategories at the lower levels inherit the properties. Let us give some examples. The property has Subordinate Concept is defined at the category Socio-Cultural Time Periods and it relates the category to itself. The reason for this is that we want this relation to hold among the instances of the category Socio-Cultural Time Periods. In other words, we want to relate a concept of time period, say Holiday, which is an (indirect) instance of the category Socio-Cultural Time Periods to another concept of time period, say Victory Day, which is also an (indirect) instance of the same category such that the first time concept is a superordinate concept of the second one.

 

To be more concrete, the concept of time period Holiday is a direct instance of the category Socio-Cultural Time Periods with Duration of One Day. As this category is a subcategory of Socio-Cultural Time Periods, it inherits the property has Subordinate Concept. The concept of time period Holiday becomes equipped with this property (because it is the instance of the category of Socio-Cultural Time Periods with Duration of One Day). Recall that the property has Subordinate Concept is defined at the category of Socio-Cultural Time Periods and it relates the category to itself, so the value of the property needs to be another instance of the category Socio-Cultural Time Periods. The concept of time period Victory Day is a direct instance of the category Turkish Time Periods with Duration of One Day. As this category is the subcategory Socio-Cultural Time Periods, concept of time period Victory Day is also an instance of Socio-Cultural Time Periods. Hence, the concept of time period Holiday as an instance of the category Socio-Cultural Time Periods with Duration of One Day is related to concept of time period Victory Day, along the has Subordinate Concept property. The meaning of this relationship can be interpreted as “the concept Holiday implies the concept Victory Day”.

 

All properties of the ontology relate the instances of the categories in the same way. That is, every instance of the ontology is either related to another instance of a category in the hierarchy or to a string, an integer or a boolean value that is an instance of the category Literal. There are eleven different properties, all of which are defined at the category Socio-Cultural Time Periods. All subcategories of the category Socio-Cultural Time Periods inherit the eleven properties Table (10) shows the properties of the ontology.

 

 

 

Recalling our previous argument, we stated that with the Ontology of Socio-Cultural Time Concepts we are not targeting at providing yet another formal description of temporal information. Instead, we want to provide additional information, which is socio-cultural temporal information, to the existing formal temporal information. We outlined how the ontology can support a temporal type system with such additional temporal information and mentioned about the requirement that the ontology needs to provide ways to relate socio-cultural temporal information to regular temporal information. We also indicated the fact that each socio-cultural time concept that is an instance of the ontology is furnished with several properties in order to fulfil this requirement. These properties are, as the table above shows, has Duration, has Fixed Calendar Date, has Variable Calendar Date, has Index, has Granularity and recurrence. Hence, each instance delivers regular temporal information about itself by means of these properties. Finally, Figure (7) shows a simple diagram that depicts the relationships between categories of the hierarchy:

 

 

This subsection has given information about the binary relations in the ontology that exist beside the taxonomic relations. We have referred to the binary relations as properties. Properties are defined at the third level of the hierarchy at the category Socio-Cultural Time Periods and are inherited to the lower levels. As such, they describe the characteristics of their instances. We have mentioned about two different kinds of properties in the ontology and described their character. A full list of binary relations has been given by means of the Binary Relations Table. Finally, the Binary Relations Diagram demonstrated the relations that hold between the category Literals and the category Socio-Cultural Time Periods as well as the binary relations that hold at the category Socio-Cultural Time Periods itself.

 

5.3.4

Instances Table

 

In this subsection we will provide a description of some instances of the ontology. In doing so, we will give information about the properties and property values of the instances at hand. For full reference please refer to Appendix D.

 

Time and time again, we have mentioned that the instances of the Ontology of Socio-Cultural Time Concepts are the concepts of time periods that necessarily have duration and socio-cultural characteristics. Socio-cultural time concepts such as Feast of Sugar, Lent or July 4th comprise the instances of the ontology. As such, every instance in the ontology is assigned to one and only one appropriate category. For example, Feast of Sugar is a time period longer than a day, which is related to the Turkish culture and which is reserved for the celebration of an Islamic feast. Hence, the time concept of Feast of Sugar is assigned to the category of Turkish-Islamic Time Periods with Duration of Longer than One Day. Put another way, the socio-cultural time concept Feast of Sugar has type Turkish-Islamic Time Periods with Duration of Longer than One Day.

 

There are ninety instances in the Ontology of Socio-Cultural Time Concepts. Each instance is assigned to a category in the manner described above. Some categories do not have direct instances. In other words, some categories have instances only in terms of the instances of their subcategories. The category Socio-Cultural Time Periods is one such example. It has six subcategories, whose instances comprise the instances of the category Socio-Cultural Time Periods. Recall that the structure of the hierarchy is a graph (DAG) and one category is allowed to have multiple parents. Thus, it is possible to find an instance (a concept of time period) starting out from different categories. For example, we can find the instance Feast of Sugar following the path: Socio-Cultural Time Periods à Socio-Cultural Time Periods of Religions à Socio-Cultural Time Periods Related to Religions with Duration of Longer than One Day à Islamic Time Periods with Duration of Longer than One Day à Turkish-Islamic Time Period With Duration of Longer than One Day and finally the instance Feast of Sugar. We can also find the same instance following another path: Socio-Cultural Time Periods à Socio-Cultural Time Periods Longer than One Day à Socio-Cultural Time Periods Related to Religions with Duration of Longer than One Day à Islamic Time Periods with Duration of Longer than One Day àTurkish-Islamic Time Periods with  Duration of Longer than One Day and finally the instance Feast of Sugar. Table (11) depicts Instances Table w.r.t. METHONTOLOGY.

 

Instances Table

 

 

Before proceeding to the implementation of the ontology in OWL, let us provide a summary of the conceptualization activity. As of now, we have produced the conceptual structure of the Ontology of Socio-Cultural Time Concepts, which is independent of any modelling language and of any platform. In other words, the ontology at this stage, is at the knowledge level and it can be implemented using any ontology language.

 

 We have started the conceptualization activity by defining a Glossary of Terms that includes the socio-cultural time periods related to nations, religions, business life & education and their characteristics. Next, we have created the Concept Classification Hierarchy, where the socio-cultural time concepts of the ontology are assigned to appropriate categories and are organized in hierarchical order w.r.t. subclass-superclass relations. Subsequently, a Concept Dictionary has been built, where detailed information about the categories of the ontology is delivered. The information includes the category name, its description, its properties, and so forth. After that a Binary Relations Table and Diagram has been presented that depict the property relations in the ontology. They exist with the taxonomic relations simultaneously. Finally, the Instances Table has been created that gives information about the instances of the ontology along with their descriptions, associated categories, properties and property values. With this final step, we have completed the conceptualization activity and produced the ontology at the knowledge level.

 

5.4	Implementation of the Ontology of Socio-Cultural Time Concepts Related to Nations, Religions, Business Life & Education in OWL

 

This section will introduce how the ontology at the conceptual level has been implemented using the ontology modelling language OWL. In other words, this section shows the mapping of the ontology from the knowledge level to the symbolic level. As mentioned formerly, OWL has been chosen as the implementation language because our ontology is intended for the Web use and OWL is the current Web standard for developing ontologies.

 

We will refer to the elements of the ontology using the OWL vocabulary. Thus, categories of the ontology are OWL Classes, the hierarchical or the taxonomic relationship is the subclass relationship. Instances of the ontology are OWL Individuals. Binary relations are properties, which can be either Datatype Properties or Object Properties.

 

Classes are organized in a hierarchical structure w.r.t. subclass relationship. Top level category (┬) is the class Thing, every class including the system classes, is a subclass of Thing. Class Time Periods is the subclass of Thing and it has two further subclasses, which are the classes Calendar Date Periods and Socio-Cultural Time Periods. Former does not have any subclasses, whereas the latter does. Class rdfs:Literal is the class that holds all the literal values (Datatype Values) such as strings, integers and booleans. As such, it is a hidden class that does not show up in the actual hierarchy. Classes contain the Individuals of the ontology, which are the concepts of time periods.

 

Properties represent binary relations that hold between the classes of the OWL ontology. There are two types of properties: the Object Property, and the Datatype Property. In our ontology, first one is a binary relation at the class Socio-Cultural Time Periods itself. Thus, an individual that belongs to this class or to one of its subclasses will be related to another individual of this class or an individual of its subclasses along this type of property.

 

Second property is a binary relation between the class Socio-Cultural Time Periods and the class rdfs:Literal. Individuals of the class rdfs:Literal are Datatype Values such as strings, integers and booleans. Thus, the relation links the individuals of the class Socio-Cultural Time Periods to arbitrary Datatype Values of the class rdfs:Literal. This type of property is called Datatype Property. Figure (8) shows the top level and the high levels of the hierarchy as well as the Object- and the Dataype Properties defined at the classes.

 

Properties have domains and ranges. This way we can restrict the classes that we want to define the properties for and we can also restrict the values that the properties can take. In our ontology, we have defined the properties only at the class Socio-Cultural Time Periods. So, it is the only domain of all properties in the ontology. There are two possibilities for the ranges of the properties. In other words there are two classes in the ontology that can be the range of the defined properties: the class Socio-Cultural Time Periods itself or the class rdfs:Literal. This means two things: First, the properties can relate the individuals of the Socio-Cultural Time Periods to other individuals of the same class (or its subclasses). Second, they can relate the individuals to the Datatype Values of the class rdfs:Literal. Figure (9) shows the domain and the ranges of the properties.

 

Finally, Figure (10) shows the Individuals of the OWL ontology. The individuals in our ontology are the concepts of time periods. Each class in the OWL ontology has individuals either directly or in terms of its subclasses. Each individual carries the properties of the class it belongs to, thus it is either related to another individual, or to a datatype value or to both along these properties.

 We conclude with presenting a piece of OWL code of the Ontology of Socio-Cultural Time Concepts that shows the class Christian Time Periods with Duration of One Day and its Individual Ascension represented above. Appendix E provides for the full source code:

 

Class Christian Socio-Cultural Time Periods with Duration of One Day