Limitations of the Expressive Power of RDF Schema(3) Cardinality restrictions E.g. a person has exactly two parents, a course is taught by at least one lecturer Special characteristics of properties Transitive property(like greater than) Unique property(like " is mother of A property is the inverse of another property(like eats" and"is eaten by) 11 Chapter 4 A Semantic Web primer
Chapter 4 A Semantic Web Primer 11 Limitations of the Expressive Power of RDF Schema (3) ⚫ Cardinality restrictions – E.g. a person has exactly two parents, a course is taught by at least one lecturer ⚫ Special characteristics of properties – Transitive property (like “greater than”) – Unique property (like “is mother of”) – A property is the inverse of another property (like “eats” and “is eaten by”)
Combining owL with RDF Schema o Ideally, OWL would extend RDF Schema Consistent with the layered architecture of the Semantic Web o But simply extending RDF Schema would work against obtaining expressive power and efficient reasoning Combining rdf schema with logic leads to uncontrollable computational properties 12 Chapter 4 A Semantic Web primer
Chapter 4 A Semantic Web Primer 12 Combining OWL with RDF Schema ⚫ Ideally, OWL would extend RDF Schema – Consistent with the layered architecture of the Semantic Web ⚫ But simply extending RDF Schema would work against obtaining expressive power and efficient reasoning – Combining RDF Schema with logic leads to uncontrollable computational properties
Three Species of OWL o W3C'sWeb Ontology Working Group defined OWL as three different sublanguages OWL Full OWL DL OWL Lite o Each sublanguage geared toward fulfilling different aspects of requirements 13 Chapter 4 A Semantic Web primer
Chapter 4 A Semantic Web Primer 13 Three Species of OWL ⚫ W3C’sWeb Ontology Working Group defined OWL as three different sublanguages: – OWL Full – OWL DL – OWL Lite ⚫ Each sublanguage geared toward fulfilling different aspects of requirements
OWL Full o It uses all the oWL languages primitives o It allows the combination of these primitives in arbitrary ways with RDF and RDF Schema ● OWL Ful‖ is fully upward- compatible with RDF, both syntactically and semantically OWL Full is so powerful that it is undecidable No complete(or efficient)reasoning support 14 Chapter 4 A Semantic Web primer
Chapter 4 A Semantic Web Primer 14 OWL Full ⚫ It uses all the OWL languages primitives ⚫ It allows the combination of these primitives in arbitrary ways with RDF and RDF Schema ⚫ OWL Full is fully upward-compatible with RDF, both syntactically and semantically ⚫ OWL Full is so powerful that it is undecidable – No complete (or efficient) reasoning support
OWL DL OWL DL ( Description Logic) is a sublanguage of OWL Full that restricts application of the constructors from oWL and rDF Application of oWL's constructors to each other is disallowed Therefore it corresponds to a well studied description logic OWL DL permits efficient reasoning support o But we lose full compatibility with RDF Not every RDF document is a legal OWL DL document Every legal oWL DL document is a legal RDF document 15 Chapter 4 A Semantic Web primer
Chapter 4 A Semantic Web Primer 15 OWL DL ⚫ OWL DL (Description Logic) is a sublanguage of OWL Full that restricts application of the constructors from OWL and RDF – Application of OWL’s constructors’ to each other is disallowed – Therefore it corresponds to a well studied description logic ⚫ OWL DL permits efficient reasoning support ⚫ But we lose full compatibility with RDF: – Not every RDF document is a legal OWL DL document. – Every legal OWL DL document is a legal RDF document