Management of heterogeneity in the Semantic Web

1. Semantic Web and Databases Atlanta, Georgia, USA April, 2006 Management of heterogeneity in the Semantic Web Paolo Atzeni Pierluigi Del Nostro

2. Semantic Web • Many languages and models exist • Interoperability is the challenge, with a generic approach Paolo Atzeni - Pierluigi Del Nostro

3. RDF Topic maps Semantic Web tecnologies Two families of standards W3C ISO Paolo Atzeni - Pierluigi Del Nostro

4. Outline • RDF and Topic maps : what they share • RDF definition • Topic maps definition • RDF vs Topic maps : differences • Model independent approach • Meta-constructs • Super model • Translation process Paolo Atzeni - Pierluigi Del Nostro

5. RDF and Topic Maps • Both RDF and Topic Maps : • consist of standard family • attempt to apply knowledge representation techniques to information management • define abstract models and interchange syntaxes based on XML • have models that are simple and elegant at one level but extremely powerful at another Paolo Atzeni - Pierluigi Del Nostro

6. RDF(Resource Description Framework) • Based on three concepts • Resource: all it is possible to describe. Each resource is identified by an URI (not only web resources) • Property: an attribute associated with the resource. • Statement: all is it possible to say about resources. It has the form of the triple <subject, predicate, object> where: • Subject: resource • Predicate: property • Object: resource/literal Paolo Atzeni - Pierluigi Del Nostro

7. RDF (example) Paolo Atzeni - Pierluigi Del Nostro

8. Topic Maps • A standard for defining knowledge structures and associating them with information resources • Topic maps are organized around the concept of Topic, which is used to represent some real-world thing • Three constructs are provided for describing the subjects represented by the topics: • Names: multiple base names to a single topic and variants of each base name • Occurrences: a topic may be linked to one or more information resources that are deemed to be relevant to the topic • Associations: have a type, can be n-ary and each topic participate with a specific role Paolo Atzeni - Pierluigi Del Nostro

9. predator prey cats predation birds role role association Topic Maps (example) occurrence occurrence Cats are furry carnivorous animals… cats.doc Birds are feathery animals… birds.doc Paolo Atzeni - Pierluigi Del Nostro

10. RDF vs Topic Maps Paolo Atzeni - Pierluigi Del Nostro

11. Our approach • Translation between Semantic Web models handled with a metamodel tecnique developed for translating schemas from a datamodel to another Paolo Atzeni - Pierluigi Del Nostro

12. Constructs: a classification • A model can be defined in terms of the meta-constructs its constructs refer to • E.g., the E-R model: • Abstract (called Entity) • Function from Abstract to Lexical (Attribute) • Aggregation of abstracts (Relationship) • Lexical types • Sets of printable values • The domain • Abstract types • Entity type, set of objects in the world • Class, set of objects in the system • Aggregation • a construction based on (subsets of) cartesian products • Relationship in the E-R model • Relation in the relational model • Function • Attribute in the E-R model • Function in a functional data model • Grouping • Hierarchies Paolo Atzeni - Pierluigi Del Nostro

13. The supermodel • A model that includes all the meta-constructs (in their most generalforms) • Each model is subsumed by the supermodel • Each schema for any model is also a scheme for the supermodel • Translations are realized within the supermodel • It needs to be extended to properly represent Semantic Web formalisms • The separation between schemas and instances is not strong Paolo Atzeni - Pierluigi Del Nostro

14. Translation rules RDF Topic maps model model S1 S2 schema schema The translation process Super model SM_RDF SM_TM correspondence correspondence translation SM_S1 SM_S2 source target source copy copy ? Paolo Atzeni - Pierluigi Del Nostro

15. The extended supermodel • SM_Abstract(schemaOID, abstractOID, name, class/instance, isProperty) • SM_Collection(schemaOID, collectionOID, name, type) • SM_ComponentOfCollection(schemaOID, componentOID, name, objectOID, collectionOID, position, lexicalValue) • SM_Identity(schemaOID, identityOID, name, type, value, objectOID, idObjectOID, idAssertionOID) • SM_AttributeOfAbstract(schemaOID, attributeOID, name, subjectOID, predicateOID, objectOID) • SM_AggregationOfAbstract(schemaOID, aggregationOID, name) • SM_ComponentOfAggregation(schemaOID, componentOID, name, aggregationOID, roleOID, memberOID) • SM_Assertion(schemaOID, assertionOID, name) • SM_InstanceOf(schemaOID, attributeOID, name, instanceOID, classOID) • SM_SubClassOf(schemaOID, attributeOID, name, subclassOID, superclassOID) • SM_Scope(schemaOID, attributeOID, name, assertionOID, scopeOID) • SM_Type(schemaOID, attributeOID, name, assertionOID, typeOID) • SM_AssertionAboutAssertion(schemaOID, assOID, name, assSubjOID, objectOID, lexicalValue) • SM_Domain(schemaOID, attributeOID, name, propertyOID, domainOID) • SM_Range(schemaOID, attributeOID, name, propertyOID, rangeOID) Paolo Atzeni - Pierluigi Del Nostro

16. Translation rules RDF Topic maps model model S1 S2 schema schema The translation process Super model SM_RDF SM_TM correspondence correspondence translation SM_S1 SM_S2 source target source copy copy ? Paolo Atzeni - Pierluigi Del Nostro

17. Correspondences RDF to SM TM to SM Paolo Atzeni - Pierluigi Del Nostro

18. Translation rules RDF Topic maps model model S1 S2 schema schema The translation process Super model SM_RDF SM_TM correspondence correspondence translation SM_S1 SM_S2 source target source copy copy ? Paolo Atzeni - Pierluigi Del Nostro

19. Translation rules • Datalog variant with: • OID invention, Skolem functions are used to generate new identifiers when needed • Elementary rules are composed in order to obtain complex translation. SM_AttributeOfAbstract ( sOID, assOID(cOID1, cOID2), N(agN, cN1, cN2), ‘null’, mOID1, mOID2) ← SM_AggregationOfAbstract(sOID, agOID, agN), SM_ComponentOfAggregation(sOID, cOID1, cN1, agOID, mOID1, rOID1), SM_ComponentOfAggregation(sOID, cOID2, cN2, agOID, mOID2, rOID2), cOID1<>cOID2 Paolo Atzeni - Pierluigi Del Nostro

20. John Smith Author predicate AuthorOf type Home_JS WebPage Schema representation inside the Super model type RDF_AllResources RDF_Resources RDF_Statement Paolo Atzeni - Pierluigi Del Nostro

21. John Smith Author Author WebPage predicate AuthorOf AuthorOf TM_Topic John Smith Home_JS role role type association Home_JS WebPage instanceOf instanceOf Author WebPage TM_Association TM_ComponentOfAssociation Schema representation inside the Super model type Paolo Atzeni - Pierluigi Del Nostro

22. Conclusions • Model independent approach to the translation • Thought for database models • Extended to embody Semantic Web formalisms • Work in progress • Currently developing the details of the translations by using the prototype ModelGen Paolo Atzeni - Pierluigi Del Nostro

23. Semantic Web and Databases Atlanta, Georgia, USA April, 2006 Management of heterogeneity in the Semantic Web Thank you Paolo Atzeni Pierluigi Del Nostro