1. 1 An Introduction To The Semantic Web

2. 2 Information Access on the Web Find an mp3 of a song that was on the Billboard Top Ten that features a cowbell. The Cowbell Project - http://www.geekspeakweekly.com/cowbell/

3. 3 The Semantic Web A Vision Of Possibilities “The Semantic Web is an extension of the current web in which information is given well-defined meaning, better enabling computers and people to work in cooperation.” -- Tim Berners-Lee, James Hendler and Ora Lassila, The Semantic Web, Scientific American, May 2001

4. 4 Importance Of URIs The Semantic Web will build on the distributed nature of the Web: –No central naming authority Schema definitions: –Not implied in applications (cf. Web browsers and HTML DTD) –Accessible in a machine-understandable format using a URI

5. 5 What’s Needed Semantics Shared schemas: conventions about declaring meaning Agreed ontologies (both terms and ‘rules’ as to how terms relate) Agreed data model (RDF) Infrastructure Schema Registries to share schemas Common syntax (XML) The Web for connectivity: URI, HTTP...

6. 6 So what is the Semantic Web? The semantic web is like the regular web, but its main unit is data, not pages Data is online Can link to other data in the same file or in other places on the web

7. 7 What are the basic units? URIs Triples –subject – predicate – object Ontology –Used for reasoning about data

8. 8 Semantic Web In the Semantic Web we will need: –Machines talking to machines – semantics need to be unambiguously declared –Joined-up data – enabling complex tasks based on information from various sources –Wide scope – from, say, home to government to commerce –Trust – both in data and who is saying it This is not going to be easily achieved

9. 9 How do we represent them? History –XML, SHOE, DAML, OIL, DAML+OIL –RDF, RDFS, OWL

10. 10 Standardization World Wide Web Consortium (W3C) http://w3.org

11. 11 Data looks like a graph

12. 12 Classes Concepts Hierarchies Multiple Inheritance allowed

13. 13 Properties (aka predicates) Properties of classes Object properties (connect instances of classes) Datatype properties (connects an instance of a class to a literal value)

14. 14 Instances Instances of a class –The class is its type Properties are used on instances Can be of multiple types

15. 15 Ontologies Generally considered a collection of classes and properties Files can contain any combination of instances, classes, and properties

16. 16 Common Ontologies Dublin Core Word Net

17. 17 Exercise 1 List 10 things about yourself –Demographic info, job, age, personal info – whatever you like

18. 18 Syntax: RDF/XML

19. 19 Using rdf:about To describe a resource: – Ending a description –

20. 20 Using rdf:ID rdf:ID is a local definition instead of a global one –

21. 21 Properties To create a property

22. 22 Exercise 2 Create descriptions of the things and properties for the attributes in your list of info –

23. 23 Property With a literal (String) Professor

24. 24 Property: With a resource as the object http://www.example.com/employment.rdf#Professor”/ OR – “#Professor”/

25. 25 Striping

26. 26 Benefits Anyone can talk about any other resource (using rdf:about) Allows for annotation and expansion of existing resources New statements are joined into the graph

27. 27 RDF Schema

28. 28 Purpose of RDF Schema The purpose of RDF Schema is to provide an XML vocabulary to: –express classes and their (subclass) relationships. –define properties and associate them with classes. The benefit of an RDF Schema is that it facilitates inferencing on your data, and enhanced searching.

29. 29 Schema and Inference With definitions of classes, domains, and ranges, information about a resource that is not explicit can be inferred from the data

30. 30 RDFS Classes Classes are categories into which resources can be grouped Members of classes are instances subClasses create a hierarchy of classes Multiple inheritance is allowed

31. 31 Properties RDFS adds domains and ranges –Limit what types of objects can be the subject of a property and what types can be the object SubProperty adds inheritance to properties –E.g. hasMother is a SubProperty of hasParent

32. 32 Multiple Domains and Ranges Multiple domains or ranges on a property are treated as intersection Example: the property hasMother has a range of Female and also a range of Parent. That means the object of the property must be both a Parent and Female

33. 33 Mapping and Aggregability Instances of the same class can easily be aggregated from separate files Using proper inferences, an instance does not need to be created as the proper type Example: Find all the Females –Jen is a Female –Irene is a Parent –Jen hasMother Irene –We now know Irene is a Female because all objects of hasMother must be female

34. 34 Other Additions Rdfs:Container, a super class of the RDF containers Labels and comments –rdfs:label - commonly used to give a real- world name to the resource being described –rdfs:comment - can be any text that you want to relate to the resource

35. 35 Web Ontology Language (OWL)

36. 36 Foundations XML RDF RDFS DAML+OIL OWL

37. 37 OWL Three Species –OWL Lite –OWL DL –OWL Full

38. 38 Equality equivalentClass equivalentProperty sameAs differentFrom allDifferent

39. 39 ZipCode equivalentClass PostalCode If zip code and postal code are supposed to be different - e.g. zip is for american addresses and postal is for foreign ones - then we can say they are different ZipCode differentFrom PostalCode Example

40. 40 Property Characteristics inverseOf –hasParent is the inverseOf hasChild TransitiveProperty –E.g. - ancestorOf - if Bob is an ancestorOf Joe and Joe is an ancestorOf Fred, then Bob is an ancestorOf Fred SymmetricProperty –E.g. if Tom is marriedTo Michelle, then Michelle is marriedTo Tom FunctionalProperty (unique value) –Wine hasMaker - hasMaker is functional (there can be only one) InverseFunctionalProperty –The inverse of a functional property - makesWine is the inverse of hasMaker and is an inverseFunctionalProperty

41. 41 Restrictions Property Type Restrictions –allValuesFrom The hasMother property has allValuesFrom the class Woman –someValuesFrom The hasChild property has someValuesFrom the class Woman Restricted Cardinality (can be 0 or 1 in Lite) –minCardinality –maxCardinality –Cardinality

42. 42 Local Restrictions on Property Ranges Instead of setting a range for a property, each class can have its own range E.g. The range of eats for vegetarians is different than for non- vegetarians Done with subclasses and a restriction …

43. 43 OWL DL and Full

44. 44 Combinations unionOf (uses ParseType) –E.g. European Union Citizenship is the unionOf the citizenship of the member states intersectionOf (uses ParseType) –E.g. Fire engines are found in the intersection of RedThings and Trucks complementOf (used like subClassOf) –E.g. the complementOf livingThings are all things that are non-living disjointWith (used like subClassOf) –E.g. Man and Woman are disjoint classes

45. 45 Intersection Example <owl:equivalentClass rdf:resource="http://www.ksl.stanford.edu/projects/DAML/UNSPSC.daml#Food-Beverage-and- Tobacco-Products"/> <owl:equivalentClass rdf:resource="http://www.ksl.stanford.edu/projects/DAML/UNSPSC.daml#Meat"/>

46. 46 ComplementOf Example