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.
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?
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