The document discusses the need for semantic technologies like ontologies to help address information overload by allowing machines to extract knowledge. It describes the evolution of semantic technologies, starting with XML providing syntactic interoperability, RDF providing a semantic grammar through assertions and relationships, and RDFS providing semantic interoperability through hierarchies and taxonomies for defining vocabulary. However, RDFS is not expressive enough to model all ontologies, so OWL was created by W3C to further extend RDFS while addressing complexity through different profiles like OWL Lite, DL, and Full.

1. Hector Quintero Casanova
University of Edinburgh
The Web Ontology Language

2. Why bother?

3. Why bother?

4. Information overload

Buried in piles of human-
readable documents.
– One trillion addresses
– 6,000,000 years to read
Put machines to work: Semantic Web:
extract knowledge for us.
= ontologies.

5. 1.Syntactic interoperability: XML

6. 1.Syntactic interoperability: XML

Fact: To spread knowledge, don't do Swahili.

XML is a “common language” or syntax which
things can be described in.
 XML is perfect for sharing meta-data and...
 … No more and no less. XML is just the
vehicle for meaning (semantics).

7. 2.Semantic grammar: RDF

Use English: “the man dog bites the”
 Problem: interpretation is not universal.

8. 2.Semantic grammar: RDF

Fact: English without a grammar is a mess.

RDF amounts to the grammar for describing
meaning: exposes relationships.
– Uses assertions: “The dog bites the man”.
– Those use a certain vocabulary: bites.
– Vocabulary must be provided.
Note: XML normally used as underlying syntax

9. 3.Semantic interoperability: RDFS

Sensible English: define status of the man

Answer: The man had a P.E.
– P.E. = Physical Examination.
 The man is alive and kicking.
– P.E. = Pleural Effusion.
 The man might be in trouble.
 Problem: subject to multiple interpretation.

10. 3.Semantic interoperability: RDFS

Fact: Cryptic English is worse than Swahili

RDF Schema provides an object-oriented
“framework” for defining vocabulary.
– Uses hierarchy and inheritance relationships.
– “Standard” actions such as subClassOf.
• RDF + RDFS = universally describe domain
– Semantically-strong taxonomies (e.g. biology)
 We don't need OWL at all?

11. 3.Semantic interoperability: RDFS

Fact: Cryptic English is worse than Swahili

RDF Schema provides an object-oriented
“framework” for defining vocabulary.
– Uses hierarchy and inheritance relationships.
– “Standard” actions such as subClassOf.
• RDF + RDFS = universally describe language
Ontology modelling domain
– Semantically-strong taxonomies (e.g. biology)
 We don't need OWL at all?

12. Ontology spectrum

13. Ontology spectrum

RDF/S cannot model all ontologies.

Enhance expressiveness of RDF/S.
 OWL = W3C's attempt to extend RDFS

But with expressiveness comes complexity
– Bad for inference rules
 W3C's solution is 3 flavours: Full, DL, Lite.

Semantic formula = XML + RDF/S + OWL

14. Semantic stack