1. Ontology

2. Philosophy The study of what is Back to the Greeks
No agreement on even the top level

3. Wikipedia:
“In both computer science and information science, an ontology is a data model that represents a set of concepts within a domain and the relationships between those concepts. It is used to reason about the objects within that domain.”

4. Use of Ontology Web 2.0 or the Semantic Web
Used to describe semantic relationships
Models of a Domain

5. Ontology Elements Individuals Classes Attributes Relations
Function terms
Restrictions
Rules
Axiom
Events
Function terms: complex structures formed from certain relations that can be used in place of an individual term in a statement
Axiom: assertions (including Rules)in a logical form that together comprise the overall theory that the ontology

6. Base Relations
ISA - is a
AKO- a kind of

7. Description Logic Decidable subset of First Order Logic
Express objects and instances
Simple axioms on relations

8. OWL XML based ontology language Three levels of semantics
OWL lite
OWL DL
OWL full (not decidable)
Based on RDF and RDFS
Triples
Base terms are URI

9. CYC A very large ontology Locally consistent
Lennet and the goal of common sense