1 An inference engine for the semantic web Naudts Guido Student at the Open University Netherlands

2 Case study

3 The layers of the semantic web

4 SGML and HTML HTML is an application of SGML. An application is a set of SGML tags and attribute. The tags are used for the presentation of the document. Here's a simple HTML document: My home page Hello there! Welcome to my home page!

5 XML Properties XML Properties Meta-language Subset of SGML Definition of tags –standardisation? Hierarchical Namespaces = mix of languages!

6 XML Example Designing Web Usability Design Internet X

7 DTD Example <!DOCTYPE book [ ]>

8 XML Schema example

9 The layers of the semantic web

Anything can be a resource. Resources have URIs. Resources have properties. Properties have values and types. An RDF document makes statements about resources and their properties. Basics of RDF

11 RDF Properties RDF is a language ==> syntax and semantics XML syntax Notation 3 syntax

A Simple Example “Jan Hanford created the J.S. Bach homepage.” The J.S. Bach homepage is a resource –It has a URI ( –It has a property The property has a type of “creator” The property has a value of “Jan Hanford”

RDF Graph Jan Hanford has the creator Resource Property Type Property Value

Translated to (simplified) RDF: Jan Hanford Resource Property Value Property Type

Namespaces added: Jan Hanford

16 RDF Schema

17 RDF Schema example <rdf:RDF xmlns:rdfs=" xmlns:rdf=" xmlns:daml=" xmlns=" Animal 2

18 The layers of the semantic web

19 Ontology Terms used to describe an area of knowledge Classes, relationships, properties, subclasses Definition of semantics Avoid tower of Babel

20 The layers of the semantic web

21 Closed world assumption –Case study: Jos is member of W3C. All members of W3C are entitled to recieve W3C-mail. Therefore Jos is entitled to recieve W3C-mail. We pose the query: Can Jim recieve mail from the W3C? Jim is not in the list  answer = no!!! Because of closed world assumption.

22 Open world assumption –Case study: I have a list of important internet sites; site A is on my list  site A is important. Site B is not on my list  site B is not important??? Conclusion : Open World is de default assumption, Closed World must be enforced.

23 The layers of the semantic web

24 Proof Proof validation, not generation Simple things: a  b, a thus b. validation: do the URI’s exist, are the steps followed in the reasoning valid?

25 The layers of the semantic web

26 Trust Build a web of trust Truth = trust I believe x Absolute truth ==> a pinguin is a bird Contradictions between trusted parties?

27 Structure of the project

28 Thesis questions 1 What is the best way for realising an inference engine so that the restrictions that are imposed by the structure of the World Wide Web on the Semantic Web are met ? can meta-logical frameworks be used to specify the inference engine of the semantic web?

29 Thesis questions 2 what optimisation techniques can be used? how can inconsistencies best be avoided? which system of logic should be followed on the internet? what is the interpretation of the logic i.e. what are its semantics?

30 Metalogical frameworks Logic + methodology used to represent other logics and to reason about their metalogical properties

31 Optimisation and consistency Reorder clauses Limit the search space Detect inconsistencies i.e. logic contradiction; might be violation of constraints

32 N3 example part 1 # $Id: authen.axiom.n3,v /10/01 00:12:34 amdus Exp :. :member. :w3cmember. :subscribed. {{:person :member :institution. :institution :w3cmember. :institution :subscribed :mailinglist} log:implies {:person :authenticated :mailinglist}} a log:Truth; log:forAll :person, :mailinglist, :institution.

33 N3 example part 2 # $Id: authen.lemma.n3,v /10/15 22:40:11 amdus Exp :. _:who :authenticated.

34 N3 example part 3 # Generated with on Sat Dec 01 02:19:27 GMT+01: # for query # given :. { :member. :w3cmember. :subscribed } log:implies { :authenticated }. # Proof found for in 3 steps (232 steps/sec)