Semantic Web Ontologies Sameer Totey 12202021 CSCI 7818

Semantic Web Ontologies Sameer Totey 12/20/2021 CSCI 7818 - Web Infrastructure, Services, and Applications 1

What is Ontology n n 12/20/2021 Branch of Philosophy that studies nature of existence Specification of a conceptualization Document or file that formally defines relations among terms Shared understanding of some domain of interest CSCI 7818 - Web Infrastructure, Services, and Applications 2

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What is Ontology for Web ? n n n 12/20/2021 A Taxonomy which defines classes of objects and relations among them A set of inference rules (Classes subclasses and relations among entities) CSCI 7818 - Web Infrastructure, Services, and Applications 5

Why Ontologies? n n Lack of a shared understanding leads to poor communication Disparate modeling paradigms, languages and software tools limit 1. 2. 12/20/2021 Interoperability Knowledge Sharing and reuse CSCI 7818 - Web Infrastructure, Services, and Applications 6

Theory n n n 12/20/2021 Usually Ontology structure is represented as a 5 Tuple O = (C, R, H, rel, A) Disjoint Sets C and R are concept identifiers and relation identifiers respectively H is the concept hierarchy. Also called Taxonomy. H(C 1, C 2) means C 1 is subconcept of C 2. H is a directed transitive relation. Rel is a function that relates concept nontaxonomically, rel : R C X C A is a set of ontology Axioms, expressed in an logical language like first order logic. CSCI 7818 - Web Infrastructure, Services, and Applications 7

Ontology Engineering n The task of developing an ontology is a typical knowledge acquisition task involving 1. 2. 3. 4. 12/20/2021 Kickoff Refinement Evaluation Maintenance CSCI 7818 - Web Infrastructure, Services, and Applications 8

Languages n n n Frame Logic Loom Ontololingua etc. Web needs XML based language : defining a language on top of XML syntax n SHOE (SHOE is an HTML-based knowledge representation language) Simple HTML Ontology Extention. XOL (Ontology Exchange Language) OML (Ontology markup language) RDFS (Resourse description framework scheme language) OIL (Ontology Interchange Language) n DAML (DARPA Agent markup language) n n 12/20/2021 There are several representation languages in the AI (machine learning, natural language processing, knowledge representation etc) community based on FOL like CSCI 7818 - Web Infrastructure, Services, and Applications 9

Editors n Tools that help create ontologies and metadata that can be used by multiple agents: u u 12/20/2021 Protégé Web. Onto Oil. Ed ONTOEdit CSCI 7818 - Web Infrastructure, Services, and Applications 10

Related issues: n n n Higher order logic based inference engines – Needed but not feasible First order logic based inference engines – feasible but limited expressive power, FOL is semi-decidable some inferences are computationally intractable Interoperability u u 12/20/2021 Bremer Semantic Translation project SKC (Stanford Scalable Knowledge Composition) project CSCI 7818 - Web Infrastructure, Services, and Applications 11

References n n n 12/20/2021 http: //www. fzi. de/wim [Development and applications of Ontologies] tutorial www. sematicweb. org www. ontologyworks. com CSCI 7818 - Web Infrastructure, Services, and Applications 12

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