The Semantic Web: Means Many Things to Many People

What is the Semantic Web? The Semantic Web is an evolving extension of the World Wide Web in which web content can be expressed not only in natural language, but also in a form that can be understood, interpreted and used by software agents, thus permitting them to find, share and integrate information more easily. It derives from W3C director Tim Berners-Lee's vision of the Web as a universal medium for data, information, and knowledge exchange.

The Story

The Layer Cake of the Semantic Web

Ontology Language ~ OSM/OWL … … 1 … …...

OSM/OWL & Logic and Proof Allow modeling to be done ontologically (high level of abstraction) Then, systematically transform the application model into predicate calculus for use in reasoning.

Transformation to Predicate Calculus: Example

Generated Predicates Object Sets Relationship Sets Room(x), Room Nr(x), Cost(x), Date(x), Guest(x), Guest Nr(x), Current Guest(x), Future Guest(x), Guarantee Nr(x) Room(x) has Room Nr(y), Room(x) has Cost(y), Guest(x) has reservation for Room(y) on Date(z), Guest(x) has Guest Nr(y) Future Guest(x) has Guarantee Nr(y)

Generated Rules Referential-Integrity Constraints  x  y(Room(x) has Room Nr(y)  Room(x)  Room Nr(y))... Generalization/Specialization Constraints  x(Current Guest(x)  Future Guest(x)  Guest(x)) Participation Constraints  x(Room(x)   1 y(Room(x) has Cost(y))  x(Cost(x)   1 y(Room(y) has Cost(x))... Co-occurrence Constraints  (  z(Guest(z) has reservation for Room(x) on Date(y))   1 w(Guest(w) has reservation for Room(x) on Date(y)))

A Valid Interpretation Object-Set Relations Relationship-Set Relations Constraints Room R1 R2 Room Nr 1 2 Cost Room has Room Nr R1 1 R2 2  x(Room(x)   1 y(Room(x) has Room Nr(y))...

Logic and Proof Prove: ItalianProf(x)  LatinLover(x) Proof (by contradiction): 1.  LatinLover(x)negation of conclusion 2.ItalianProf(x)premise 3.ItalianProf(x)  Italian(x)ontologically given 4.Italian(x)modus ponens (2&3) 5.Italian(x)  Lazy(x)  Mafioso(x)  LatinLover(x)ontologically given 6.Lazy(x)  Mafioso(x)  LatinLover(x) modus ponens (4&5) 7.Lazy(x)  Mafioso(x)resolution (1&6) 8.ItalianProf(x)   Lazy(x)ontologically given 9.  Lazy(x)modus ponens (2&8) 10.Mafioso(x)resolution (7&9) 11.Mafioso(x)   ItalianProf(x)ontologically given 12.  ItalianProf(x)modus ponens (10&11) 13.Fcontradiction (2&12)

RDF & RDFS ~ the Heart of OWL RDF (Resource Description Framework) –A triple model where every assertion is decomposed in three parts: (subject, predicate, object) for instance (tutorial.php, author, "Fabien"). –The subject is a URI identifying a resource. The predicate is a binary relation identified by a URI. The object is either a URI identifying a resource or a literal value. –Each triple can be seen as a labeled arc and joining these arcs one obtains a graph that describes URI-identified resources and their relations. RDFS (RDF Schema) –RDFS is a set of primitives to describe lightweight ontologies –RDFS allows us to: name and declare a vocabulary (name resource types and binary relation types called properties); specify the signature of properties (type of the domain i.e. type of the subject and type of the range i.e. type of the object); specify the (multiple)-inheritance links between the types of classes (subClassOf); specify the (multiple)-inheritance links between the types of properties (subPropertyOf);

RDF Graph (How to think about RDF)

SPARQL Specifies queries over an RDF triple store Triple stores have an OWL/RDF schema Example: get names and, if available, gender and birthdate of people born in the 1870’s. (An RDF Query Language) SELECT ?Name ?Gender ?BirthDate WHERE { ?IndividualURI gc:name ?Name. OPTIONAL { ?IndividualURI gc:gender ?Gender ; gc:born ?Birth. ?Birth gc:date ?BirthDate }. FILTER REGEX(?BirthDate, "187\\d") }

Genesis