04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

1

Semantic Web - Ontologies

Sameer Totey

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

2

What is Ontology

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

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

3

Acrobat Document

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

4

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

5

What is Ontology for Web ? A Taxonomy which defines classes

of objects and relations among them

A set of inference rules (Classes subclasses and relations

among entities)

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

6

Lack of a shared understanding leads to poor communication

Disparate modeling paradigms, languages and software tools limit

1. Interoperability

2. Knowledge Sharing and reuse

Why Ontologies?

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

7

Theory 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(C1,C2) means C1 is subconcept of C2. H is a directed transitive relation.

Rel is a function that relates concept non-taxonomically, rel : R C X C

A is a set of ontology Axioms, expressed in an logical language like first order logic.

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

8

Ontology Engineering

The task of developing an ontology is a typical knowledge acquisition task involving

1. Kickoff

2. Refinement

3. Evaluation

4. Maintenance

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

9

Languages There are several representation languages in the AI

(machine learning, natural language processing, knowledge representation etc) community based on FOL like

Frame Logic Loom Ontololingua etc.

Web needs XML based language : defining a language on top of XML syntax

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)

DAML (DARPA Agent markup language)

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

10

Editors

Tools that help create ontologies and metadata that can be used by multiple agents: Protégé WebOnto OilEd ONTOEdit

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

11

Related issues: 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 Bremer Semantic Translation project SKC (Stanford Scalable Knowledge Composition) project

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

12

References

http://www.fzi.de/wim [Development and applications of Ontologies] tutorial

www.sematicweb.org www.ontologyworks.com

04/19/23 CSCI 7818 - Web Infrastructure, Services, and Applications

13