ABSTRACT In this paper, we describe an engineering process of building an ontology for Yorùbá Cultural Heritage (YCH). The aim of this work is to design and implement an ontology representing knowledge embedded in YCH as a digital (documentation) resource. Building an indigenous knowledge management system requires a formal representation of YCH concepts and their relationships. Even so, YCH resources are endangered in the face of globalisation, westernisation and inter-ethnic interaction with the available few locked up in memory institutions. A combination of observation, consultation, documented materials and prototyping was used for the knowledge elicitation from domain experts. Formal Concept Analysis approach was adopted for the design aspect of the work. And, Protégé was used for the implementation. The resulting ontology was jointly validated with both the domain experts and the ontology experts. The final ontology represents the documentation of the elicited knowledge of the YCH domain. In conclusion, the formal digital documentation resulting from the study is a useful software artefact for the development of a semantic application for Yorùbá heritage domain. Keywords: Yorùbá cultural heritage; Knowledge Management; Knowledge Representation; Ontology African Journal of Computing & ICT Reference Format: J.A. Hassan, O.A. Odéjóbí, B.A. Ògúnfolákàn & A. Adéjùwón (2013). Ontology Engineering in Yorùbá Cultural Heritage Domain. Afr J. of Comp & ICTs. Vol 6, No. 5. Pp181-198.
1. INTRODUCTION
There has been renewed interest in African cultural heritage for academic purposes and the development of intelligent cultural heritage system. Yorùbá cultural heritage (YCH) resources, like those of other African cultural heritage, are endangered in the face of inter-ethnic interaction, westernisation and globalisation. Moreover, the available few heritage resources are locked up in memory institutions such as museums, libraries and archives.
Thus, YCH domain knowledge is still largely implicit and searching for information in this vast and heterogeneous domain is often challenging. More challenging and complex, however, is the formal representation of the domain knowledge. The associated implicitness, vastness, heterogeneity and complexity provide an excellent case for a research in Semantic Web technologies in general and ontology engineering in particular.
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Hence, the need for the formal representation and digital documentation of this heritage emerges in the context of modern global information and communication technologies (ICT).
1.1 Research Questions
With facilities provided by the global ICT, the following questions emanate: (i) Can the knowledge of the identifiable constituents of the YCH domain be formally rep-resented? (ii) If the above is possible, can the representation be reduced to a digital resource for a global audience and support the development of a semantic application program?
1.2 Aim and Objectives
The study reported in this paper addresses the computational representation of the elicited consensus knowledge of YCH domain. The elicited knowledge is reduced to an ontology, which is a key enabling technology for Semantic Web. The specific objectives are to (a) elicit knowledge of Yorùbá cultural heritage; (b) design an ontology for the knowledge elicited in (a); (c) implement the ontology designed in (b); and (d) validate the ontology implemented in (c).
1.3 Outline
Having described the background of the study, the problems addressed, research questions and the aim and objectives, the rest of this paper is organised as follows. In Section 2, we place the YCH resources within a wider spectrum of knowledge engineering, semantic computing and cultural studies through the review of related researches. Section 3 highlights the research methodology deployed. Next, Section 4 outlines the body of knowledge of Yorùbá heritage narratives with elicitation techniques employed. Section 5 details the ontology design approach adopted in achieving the design objectives of the study and Section 6 discusses our ontology implementation approach. Finally, Section 7 presents the summary, conclusion and future work direction. 2. RELATED WORKS
This section discusses the study area with a view to establishing the research framework. We present a review of related works in the ontology design and implementation in the domain of cultural heritage in particular. 2.1 Cultural Heritage Cultural heritage domain knowledge is largely implicit and multi-disciplinary [7, 22]. Nevertheless, the elicitation and explicit representation of this knowledge type are required for heritage data analysis, ontology design and implementation toward building ontology for Yorùbá heritage domain. Associated with the cultural heritage collections - sourced from
anthropological expeditions and archaeological excavations [25, 27] – are the intangible aspects of YCH such as stories, folktales, myths, legends, beliefs, etc. These collectively form the museum, monument and iconic narratives.
2.2 Yorùbá Knowledge Representation
Knowledge of cultural heritage resources has from time immemorial been represented by the Yorùbás orally in folk dirges, Ifá literary corpus and lineage oríkìs [5, 54, 47], visually in sculptures and other handicrafts [3, 15] and encryptedly in àrokò [50]. Nonetheless, these oral, visual and cryptic representations of knowledge are implicit. In order to digitally document these cultural heritage resources [16] and harness the potential of Semantic Web technologies for knowledge sharing and re-use across disparate system boundaries, explicit representation of the knowledge of YCH is needed.
2.3 Research Context
Ontology engineering can be defined as the methodological study of a universe of discourse and corpus analysis for further knowledge elicitation and the computational representation of the domain knowledge for the purpose of knowledge management and development of intelligent information systems. Ontology engineering for cultural heritage is, therefore, situated within Artificial Intelligence most especially Semantic Web technologies and Knowledge Representation in particular. Thus, this paper is under the wider spectrum of Computer Science and Engineering as illustrated in Figure 1.
2.4 Related Projects
Researchers in Computer Science and Engineering have been probing the potentials of semantic technologies in cultural heritage domain [37, 36, 33, 35, 42] since the early 90s when the foundation of the Semantic technologies and the integral knowledge representation language was laid [13]. Doerr in 2003[21] established the first upper domain ontology for cultural heritage data known as Conceptual Reference Model (CRM). A major limitation of CRM is that it is complex, thus, the use of Web Ontology Language (OWL) for the representation of collective cultural knowledge has since been proposed [43]. The works of Isaksen [37] and Hyvönen [34] informed the separate and different method of treating data from the private and public domain. Damino and Lieto [19] represent the complex interplay of museum narratives and relations implemented in the Labyrinth project, in the OWL ontology.
2.5 Ontology Development Methodology
Formally, an ontology can be defined as a 5-tuple O = <C, R, F, A, I > [40] where: C: a finite set of heritage concepts organised in taxonomy. R: a finite set of narrative relations between the concepts. F: Functions represent the defined operations in the concepts A: a set of axioms. I: Instances of an object.
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Ontology development requires the following: (i) A Development Methodology: There is not yet a standard methodology for ontology development [38, 1, 18]. (ii) A Knowledge Representation Language: There are many [18] but OWL emerges as the de-facto lingua franca [6] since 2004. (iii) An Ontology Development Editor: There are over 150 editors [45] from which Protégé stands out for being free and applicable to diverse domains of varied complexity. Formal Concept Analysis (FCA) with its extension Relational Concept Analysis (RCA) has been found very useful among the domain data analysts and the ontology designers [32, 12, 11]. The same is true for the YCH data analysis and ontology design. Ontologies are engineering artefacts [18], therefore, they need to be thoroughly evaluated. However, ontologies by their declarative nature present a number of challenges. In fact, they can be used in ways unexpected by the original creator(s). Ontology verification, validation and evaluation have not been found automatable; therefore, these have remained tasks for a human level intelligence for domain and ontology experts [12, 55]. To aid the domain and ontology experts in the joint ontology validation, an ontology graphical visualization OWLGrEd is a prime choice for its familiar UML-styled representation which is lacking by its peer visualization tools [9, 10].
3. RESEARCH FRAMEWORK Based on the above related works, the knowledge of Yorùbá heritage was elicited from the domain experts using a combination of observation, consultation, prototyping and critique of documented materials. Formal Concept Analysis was used for the ontology design of the knowledge elicited. The ontology designed was implemented using Protégé-OWL Editor and, this was repeatedly refined over a number of iterations until a satisfactory implementation of the Yorùbá heritage domain ontology was obtained. The implemented ontology was jointly validated by both the domain experts and the ontology experts for accuracy and completeness with the aid of OWLGrEd. 4. CORPUS STUDY This section describes the corpus analysis carried out for the purpose of gaining some understanding required for knowledge elicitation. Described as well are the documented sources of knowledge about Yorùbá heritage and proposed taxonomy for YCH resulting from the corpus analysis. 4.1 Heritage Body of Knowledge The term Yorùbá has been traced to the Yóòba in the Yóòba bàbá e, Yóòba ìyá e phrases, angry irritating abuse among the Òyó people that northern neighbours discovered were endemic in the community [54]. Later, the Hausas popularised it as Yariba or Yarba. Then, in the 18th century, Samuel Àjàyí Crowther (1809 – 1891) and other Creole Missionaries continued its spread. Since then, the term Yorùbá identifies both the language and its over thirty-two dialect variants [4, 8, 28, 41, 20] and the people speaking the language with understandably similar customs, traditional practice and worldview [3, 17, 30]. The Yorùbás have been living in advanced urban kingdoms for more than 1,500 years [46] with population distribution across South-Western states of Nigeria, some regions in West Africa and others in Diaspora, and all over the world as economic migrants making over 35 million people worldwide [24]. The Yorùbás are generally known for world-acclaimed heritage sites, antiquities and ifá literary corpus. Samples of antiquities of Yorùbá origin can be found in museums all over the world most especially Europe and America and particularly in Nigeria. There are sample collections of Yorùbá antiquities in the Èsìé Museum opened in 1945, Jos Museum in 1952, Oron Museum (1958), Benin Museum (1960), Kano Museum (1960) and Kaduna Museum (1975) and particularly in the Ifè Museum (1954) literally renowned for world-wide acclaimed terracotta sculptures and stone monoliths/obelisks [23], Lagos Museum (1957) and Òwò Museum (1968) [31]. These museum collections depict cultural materials of spiritual, ancestral and kingship symbolism fashioned, conserved and preserved in community and household temples and palaces of kings/queens under the upkeep of the head of every household, priests of the sacred groves and kings or their curator designates [25, 51]. The evolving Yorùbá belief and value system [14] is deep-rooted with over 201 òrìsà (principals) and irúnmolè
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(principalities) [53], some with multiple identities [52]. Associated with these pantheon (òrìsàs and irúnmolès) are festivals among various groups with their various folk dirges [2, 48, 49] and names. Usually, some names are associated with the belief system and mood of the parents hoist around the circumstance of birth (orúko àmútòrunwá), township (ìlú) and lineage (ìdílé).
4.2 Heritage Knowledge Elicitation
Toward accomplishing one of the principal objectives in the research, we made visits to both the National Museum of Ifè, Enuwá, Ilé-Ifè and the OAU-based Martin Awórinléwò Odéyemí Museum of Antiquities and Contemporary African Art. Such data as Name, Origin, Component(s), Usage, Background Information and Size were collected and collated. Further survey of literature was conducted on these cultural items to elicit more knowledge and gain much needed under-standing. Yet, other documented materials, classic and epic Yorùbá films and indigenous fictional stories are relevant in inventorying the intangible aspects of YCH From the combination of documented materials, observation and consultation, with samples shown in the Appendix, a prototype documentation of research findings was presented to the domain experts for validation and further knowledge elicitation. The body of knowledge elicited revealed some significant narrative and translation errors. Few are discussed below. For instance about Orí Olókun, Drewal and Schildkrout [24] wrote on page 27 of Kingdom of Ifè: Sculptures from West Africa that “It probably represents an Oòni and in its original form, had nothing to do with Olókun"; however, elicited knowledge reveals that, Orí Olókun depicts Olókun who apart from being the first wife of Odùduwà, acquired tremendous wealth through beads making. Although, barren, Olókun left the palace after a quarrel with other wives: Omitótó, Àtìbà and Òsàrà. Thereafter, she lived, died and was buried at Olókun grove where she was being venerated as the patron Òrìsà of beads making. Accordingly, Orí Olókun is used in annual rites honouring Olókun. Also, on page 51 on the Oòni Láfogídò bust, ìwo etù was wrongly translated as forest buffalo horn instead of antelope horn.
5. ONTOLOGY DESIGN
In this section, we describe the various ontology design approaches for modelling YCH domain.
5.1 Ontology Building
Building an ontology is an iterative process as shown in Figure 2 where identification of domain concepts comes first. This is followed by associated narrative relations from museum narratives. Then comes the structure for identifying concept and narrative relations hierarchically. The final process describes axiomatically the concepts formally using other concept(s) and narrative relation(s). Each of the phases can further be refined as the need arises in subsequent iterations.
This is formally expanded in the Algorithm V.1 involving Formal Concept Analysis design tool and Protégé ontology editor to be used in defining classes and class hierarchies, value restrictions, relationships between classes and properties of these relationships.
Figure 2: Iterative Nature of Ontology Building
Figure 3: Top-Level Model of Yorùbá Heritage Ontology
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For every cultural heritage object selected, other identifiable related objects and/or subjects with narrative relation(s) found in the museum narratives are noted. For each of the relations identified, a crosstab relationship is designed using FCA or RCA as the case may be. Finally, each of the identified cultural heritage objects and subjects is formally described in the Protégé implementation. This is repeatedly refined until a satisfactory implementation is obtained. The domain and application specific ontology described in this section represents an explicit specification of the conceptualisation of museum artefacts and artefact collections. The top-level model is depicted in Figure 3 showing the museum artefacts in relations with the heritage subjects/objects (festival, dirge, legend and pantheon among others) within the context of which the artefacts are meaningful.
5.2 Working Taxonomy
Taxonomy, being the backbone of every ontology, needs to be designed for both tangible and intangible aspects of Yorùbá cultural heritage. Toward that goal, a middle-out approach is adopted for ease, contingency and the convenience comparative advantages it offers over both top-down and bottom-up approaches [39]. Artefacts Canada Taxonomy Model (Figure 4) was also found adaptable. Using the model as a basis and the middle-out approach, we started with the most important concepts with subsequent generalisation (Super-concepts) and specialisation (Sub-concepts). Accordingly, the taxonomy of Yorùbá Cultural Heritage shown in Figure 5 emerged. On the basis of Object Type, cultural heritage can be broadly divided into tangible and intangible heritage. On the same basis as well, tangible heritage was categorised into immovable and movable heritage.
Figure 4: Artefacts Canada Taxonomy Model [Source: 44]
Immovable heritage, on the basis of Subject Represented, can be divided into monuments and groves and temples; while, movable heritage or museum artefact was divided into sculpture, tools and implements, and photos and paintings on the basis of Object Type; on the basis of Material, sculpture can be divided into inorganic, organic and composite sculpture; tools and implements were divided into household tools and vocational tools, and photos and painting were divided into rare artefacts and heroes and heroines on the basis of Subject Represented. On the basis of Style and Period, monuments can be sub-divided into ancient, historical and intentional monuments. But, on the basis of Material, inorganic sculpture can be sub-divided into bronze, brass, iron, terracotta, stone, mud and glass sculptures; also, organic sculpture can be sub-divided into ivory, shell, wooden, calabash and leather artefacts. The intangible cultural heritage, on the basis of Subject Represented, was categorized intocustoms and tradition, folklore, language and oral literature. Subject Represented was the only criterion used in classification of various subjects such as festivities, coronation, enactment festivals, kingdom days and chieftaincy; passage ceremonies, birth, marriage, initiation and funeral; folklore, folk dirges, myths and legends, and folk tales; language, dialects, adages, riddles, tongue twisters, and figure of speech. On the basis of Subject Represented as well, folk dirges can be sub-divided into communal dirges, devotional dirges, enactment dirges, general dirges, vocational dirges and lineage dirges. Thus, instances were found for every taxonomy node from the over 900 cultural heritage items. As typewriten in Table 1 of the Snapshot of Museum Narratives above, the 33 listed narrative relations/object properties as shown in Table 2 were identified among the over 900 cultural heritage objects and associated with 237 concepts/classes with 5 inverse properties and 4 equivalent object properties.
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Table 1: Snapshot of museum narratives and derivation of
narrative relations These narrative relations are useful in formal descriptions of cultural heritage objects as follows: (i) OriOlokun isDepicting only Olokun (ii) Olokun isWorshippedIn some (BeninRepublic and Togo and Edo and Brazil and Yorubaland and Cuba) (iii) EdiFestival isEnactedInCommemorationOf only (Moremi and Oluorogbo) (iv) Oduduwa isLegendaryFor some (EstablishedTheK-ingdomOf some (IleIfe)) (v) IgbinDrum isAnInsigniaOf only Obatala (vi) IleIfe isRenownFor some (TerracottaSculpture and StoneMonoliths) (vii) Egungun OriginatedFrom some Oyo (viii) Egungun isDepictedBy some EkuEgungun (ix) OrangunOfIla isSiblingOf some OlowuOfOwu (x) OwaObokun isKinOf some OnipopoOfPopo
(xi) EfunsetanAniwura isFamousFor some Feminism (xii) OrisariyibiOgedengbe isLegendaryFor some (defend-edTheKingdomOf some (Ijesaland)) 5.3 Data Analysis Using FCA Toward an enhanced and objective ontology of Yorùbá Cultural Heritage, the data collected and knowledge elicited were analysed using Formal Concept Analysis (FCA) with its extension, Relational Concept Analysis (RCA) employed in the ontology design for Yorùbá cultural heritage. Table 2: Snapshot of Museum Narratives
Formal Concept Analysis Formal Concept Analysis (FCA) is a branch of mathematical order theory, or more precisely, an applied branch of lattice theory with focus on a special type of lattices that are obtained from binary relations, called formal contexts [32]. 1) Formal Context Formal contexts are the underlying data structure of FCA. They can either be represented in the form of a cross table or in the form of a concept lattice. A formal context is a triple K := G, M, I > where
� G : a set of objects e.g. Yorùbá cultural objects � M : a set of unary attributes � I : a binary relation defined on the Cartesian product
G x M i.e. each of the 33 narrative relations (Table 2)
Museum Attendant: This is Orí Olókun (pointing to the artistic impression of Orí Olókun) depicting (isDepicting) Olókun who is the first of the wives of Odùduwà. Olókun is celebrated (isCelebratedIn) as the patron òrìsà of beads making. She is worshipped in (isWorshippedIn) Benin Republic, Togo and among the Edos and the Yorùbás. She is associated with Omitótó, Àtìbà and Òsàrà as co-wives. Olókun is one of the cultural heroes and heroines of Ilé-Ifè. Others are Odùduwà, Òrànmiyàn, Sàngó, Morèmi. Èdì festival is enacted in commemoration of (enactedInCommemorationOf) heroic act of Morèmi in sacrificing her only son, Olúrorogbo. Ilé-Ifè is renown for (isRenownFor) terracotta artefact such as Orí Olókun and stone monolith such as Òpá Òrànmíyàn. Òpá Òrànmíyàn depicts (isDepicting) Òrànmíyàn who is descendant of (isDescendantOf) Odùduwà. Odùduwà is legendary for (isLegendaryFor) establishing the kingdom of (establishedTheKingdom) Ilé-Ifè. While, Òrànmíyàn is legendary for establishing the kingdom of Òyó. Egúngún originated from(OriginatedFrom) Òyó and is depicted by (isDepictedBy) Èkú which is made of (isMadeOf) leather, textile etc. Odùduwà dynasty is preceded by Obàtálá dynasty. Ìgbìn drum is an insignia of (isAnInsigniaOf) Obàtálá. Legend has it that Òràngún of Ìlá is sibling of (isSiblingOf) Olówu of Òwu. And, Owá Obòkun is kin of (isKinOf) Onípópó of Pópó. etc. In Ìbàdàn, Efúnsetá Aníwúrà is famous for (isFamousFor) feminism but infamous/notorious for (isInfamousFor/isNotoriousFor) human rights abuse. Òrìsàríyìbí Ògèdèngbé is legendary for defending the kingdom of (defendedTheKingdomOf) Ìjèsàland against external aggression.
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When representing a formal context in form of a cross table, the left column represents the object set G, the upper row represents the attribute set M, and the cross cell values represent the
relationship I forming a bi-partite graph ( I G x M) as shown in Table 3.
Using FCA mathematical formalism, a concept lattice can be derived from a formal context. In a concept lattice, each node represents a formal concept, and the ascending path of line segments represents the subconcept-superconcept ( ) relationship. FCA build a concept lattice from a binary table Objects x Attributes where a maximal set of objects share a maximal set of attributes. Data is represented in formal context which consisting of a set of objects (X), a set of attributes (A), a binary relation (B), and the incidence relation (I) that determines whether or not an object has an attribute. They are usually visualised as cross-tables as shown in Table 3. For example, the cross (x) in the first row and second column of Table 3 implies that there exists an incidence relation isMadeOf between the object Orí Olókun and the attribute Terracotta. The absence of a cross, hoever, implies that there exists no incidence relation isMadeOf between the object Orí Olókun and the attribute Metal. In classical formal contexts, it is not possible to express that it is unknown whether Orí Olókun is made of Wood. Thus, from a Description Logic viewpoint, formal contexts have closed-world semantics.
5.4 Formal Concept
The notion of a formal concept is fundamental in FCA. Formal concepts are particular clusters in cross-tables, defined by means of attribute sharing. The concept Antiquity can be seen as a set of cultural heritage objects (concept’s extent) that are characterised by a set of attributes (concept’s intent). A formal concept of a formal context, K is defined as a pair (A, B) where
� A: the extent of the concept i.e. all the objects e.g. Ifè terracotta art belonging to the concept Sculpture.
� B: the intent of the concept i.e. all the attributes of Sculpture concept shared by Ifè terracotta art.
The concept of Ifè terracotta arts is a sub-concept of the concept Sculpture i.e. the set of Ifè terracotta arts is included in the set of Sculpture (inclusion of the concept’s extent) and the attributes of Sculpture are included in the attributes of Ifè terracotta arts (inclusive of the concept’s intent). In a practical application like this, what we have are multifarious attributes and, therefore, many-valued context represented by a 4-tuple <G, M, W, I > with M being the set of many-valued attributes, W, the set of attribute values, and I is a ternary relation defined on the Cartesian product G x M x W forming a tripartite graph (I G x M x W).
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Relational Concept Analysis (RCA) is an extension of Formal Concept Analysis wherein relations between such objects of YCH are taking into consideration [29]. RCA build a concept lattice from binary tables Objects x Attributes and Objects x Objects. Data is represented in RCA as a relational context which consists of a set of objects (X), another set of other objects ( ),
and a binary relation, the incidence relation (X ) which determines whether an object, x X, is related to another object, y . They are usually visualised as cross-tables, X x like in Table 4. For example, the cross (x) in the seventh row and second column of Table 4 implies that there exists a relation of isAssociatedWith between the object Orí Olókun and the object Olókun. The absence of a cross in the next column implies that there exists no relation of isAssociatedWith between the object Orí Olókun and the object Òrúnmìlà. RCA provides a relational structure that can be represented as ontology concepts within a knowledge representation formalism such as Description Logics (DLs).
However, neither Formal Context nor Relational Context can clearly show incidence of mutual exclusivity and mutual inclusiveness. These and other complex representations are logically describable with DL and demonstrable during the implementation phase. Examples of such complex representations are:
(i) Olokun isWorshippedIn some (BeninRepublic and Togo and Edo and Brazil and Yorubaland and Cuba)
(ii) EdiFestival isEnactedInCommemorationOf only (Moremi and Oluorogbo)
(iii) Oduduwa isLegendaryFor some (EstablishedTheKingdomOf some (IleIfe))
(iv) OrunmilaDisciple isAlsoRecognisedBy only (YellowBeads and (BrownBeads or GreenBeads))
(v) IleIfe isRenownFor some (TerracottaSculpture and StoneMonoliths)
(vi) Oranmiyan isLegendaryFor some (EstablishedTheKingdomOf some (Ibini and Oyo and Ikoyi and Iresa and AhiroOko and IleIgbon))
(vii) OrisariyibiOgedengbe isLegendaryFor some (defendedTheKingdomOf some (Ijesaland))
6. ONTOLOGY IMPLEMENTATION In this section, Protégé implementation of Yorùbá heritage domain ontology and validation process are presented.
6.1 Protégé OWL Implementation Ontology implementation with Protégé-OWL Editor 4.2 is an iterative process as shown in Figure 2 below:
(i) 237 domain concepts were identified from the Yorùbá
heritage resources (Figure 5) (ii) 33 narrative relations were identified and defined as
shown in Table 2 (iii) The 237 concepts were arranged hierarchically as
shown in Figure 6. (iv) The 33 relations were arranged hierarchically as
shown in Figure 7
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(v) Each of the 237 concepts were formally defined (as shown in Figures 9, 10, 12 etc.)
6.2 Implemented Description of Classes The ontology design using Formal Concept Analysis and Relational Concept Analysis does not completely represent some salient knowledge elicited. All of such knowledge are left to be shown in the Protégé OWL implementation. Implementation of knowledge elicited show varying degrees of complexity. There are instances where mutual inclusiveness and/or mutual exclusiveness is/are involved. In addition, as noted in some class descriptions, the relation incidences are combined. Figure 8 shows the Protégé implementation of knowledge elicited about the Olójó Festival which is one of the straightforward class descriptions showing a 1-to-1 relation between related concepts:
� OlojoFestival isCeleberatedIn only Ife A similar 1-to-1 relation between related concepts is Ìgbìn drum and Obàtálá represented as:
� IgbinDrum isAnInsigniaOf only Obatala Egúngún and Òyó, another 1-to-1 OriginatedFrom relation; Egúngún and Èkú Egúngún in 1-to-1 isDepictedBy relation:
� Egungun OriginatedFrom some Oyo � Egungun isDepictedBy some EkuEgungun
Figure 9 shows the class description of Èkú Egúngún with mutually inclusive components showing a 1-to-many isMadeOf relation between relating concepts as well as such 1-to-many relations in isRenownFor and isEnactedInCommemorationOf:
� EkuEgungun isMadeOf some (Glass and Leather and Paint and Textile and Thread and Wood)
� IleIfe isRenownFor some (TerracottaSculpture and StoneMonoliths)
� EdiFestival isEnactedInCommemorationOf only (Moremi and Oluorogbo)
Figure 10 shows the class description of Ìrókè Ifá, made of either Wood or Bronze with a mutually exclusive 1-to-1 relation between the relating concepts:
� IrokeIfa isMadeOf only (Wood or Bronze) and Osé Sàngó, made of either Wood or Iron also shows a mutually exclusive 1-to-1 relation between the relating concepts
� OseSango isMadeOf only (Wood or Iron) Figure 11 represents an example of combination of mutual inclusiveness and exclusiveness as in the isAlsoRecognisedBy relation in formally describing the Òrúnmìlà disciples:
� OrunmilaDisciple isAlsoRecognisedBy only (Yellow-
Beads and (BrownBeads or GreenBeads)) Figure 12 shows the class description of Òrànmíyàn with combined relations: isLegendaryFor and EstablsihedTheKingdomOf:
� Oranmiyan isLegendaryFor some (EstablishedTheKingdomOf some (Ibini and Oyo and Ikoyi and Iresa and AhiroOko and IleIgbon))
The legendary Odùduwà:
� Oduduwa isLegendaryFor some (EstablishedTheKingdomOf some (Ileife))
And for Òrìsàríyibí Ògèdèngbè, Agbógungbórò of Ìjèsàland: � OrisariyibiOgedengbe isLegendaryFor some (defend-
edTheKingdomOf some (Ijesaland))
Figure 6: The Class Hierarchy for Yorùbá Heritage
Ontology
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Oranmiyan isLegendaryFor only (EstablishedTheKingdomOf some ( Ibini and Oyo and Ikoyi and Iresa and Ahiro Oko and Ile Igbon))
Figure 12: The Class Description View with Combined Relations: Òrànmíyàn
7. Summary and Conclusion
In this paper, we have presented the study and analysis of YCH with the view to eliciting embedded knowledge in the museums and monuments of Yorùbá antiquities and their narratives. We have also pointed out and discussed the complexities in formally documenting the Yorùbá heritage knowledge. We have presented the techniques used for knowledge elicitation. We have, also, presented the varieties of class descriptions implementable to demonstrate varying complexities inherent in Yorùbá heritage knowledge representation. The results of this study have general application not only in the cultural heritage and Semantic Web, but also in heritage domain ontology engineering. They are also applicable, by and large, in facilitating the sharing of information between different agents and interfacing user and data in semantic web projects on YCH. The principle and methodology presented in this paper can be adapted, in general, to Africa heritage museums, monuments, memorabilia, library, iconic and archival resources reducing same to digital resource and made accessible for a global audience using Information and Communication Technologies.
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Appendix A: Sample Museum Artefacts of Yorùbá Antiquities
Origin: Olókun Grove, Ilé-Ifè Component(s): Terracotta Size: Height: 133/4in (35cm) Usage: In annual rites honouring Olókun, Ilé-Ifè Background Info.: Olókun is the first of the wives of Odùduwà. She acquired a lot of wealth through beads business but barren. She left the palace after a quarrel with her co-wives. She lived, died and was buried at Olókun grove where she was venerated as the patron Òrìsà of beads making. She is worshipped in Benin Republic, Togo and among the Edos and the Yorùbás. In African diasporic religions, Olókun is looked upon as the patron Òrìsà of the descendants of theTrans-Atlantic Slaves. In Lagos, Èyò Olókun masquerades are among the main attractions at the Èyò festival. Other Info.: Her co-wives are Omitótó, Àtìbà and Òsàrà
Origin: Wúnmoníjé Compound, Ilé-Ifè Component(s): Terracotta Size: Height: 143/8 in (37cm) Usage: Bust of Oòni Láfogídò. Background Info.: The Oòni Láfogídò is shown wearing an abundance of decorations consisting of beads, metalwork and ivory with an elaborate crest on his crown. One of the many bracelets is decorated with three human skulls. The imposing figure is the upper part of a broken full figurine shown below. Other Info.: Oòni Láfogídò is the 9th Ifè ruler.
Origin: Ìta Yemòó, Ilé-Ifè Component(s): Bronze Size: Height: 191/4in (49cm) Usage: Figurine of Oòni Láfogídò. Background Info.: The complete full figure known to have survived from Ifè. It represents Oòni Láfogídò in regalia worn between accession and coronation. His wrapper, with a woven or embroidered edge and held by a knotted sash tied to the left hip, is an example of the elaborate textiles Ifè rulers wore in the 14th century. Other Info.: Oòni Láfogídò is the 9th Ifè ruler.
Origin: Ifè Palace, Ilé-Ifè Component(s): Terracotta Size: Height: 143/8in (37cm) Usage: Patron of Oòni’s courtiers. Background Info.: This head represents Lájùà, the chamberlain to Oòni Láwórókolókin - one of the earliest rulers of Ifè. Lájùà is regarded as the patron of palace servants. The decline in Ifè arts and crafts industry was wrongly attributed to his alleged treacherous act of usurped the throne after the Oni’s death by donning the Oòni’s regalia or setting up an effigy in the likeness of the dead Oòni after hiding the Oòni’s dead body. After the act was discovered the next Oòni was said to have ordered the execution of all the sculptors and the courtiers for conniving and treachery. There is no iota of truth in that story as demonstrated by [26]. Other Info.: Lájùà is celebrated as the patron of the Oòni’s courtiers .
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