1. 1June 7, 2004Ontologies for interoperability1 Ontology-based data integration Maurizio Lenzerini Dipartimento di Informatica e Sistemistica “A. Ruberti” Università di Roma “La Sapienza” DASI ’06: Phd School on Data and Service Integration Bertinoro, December 11–15, 2006

2. 2Ontology-based data integration Data integration architecture

3. 3Ontology-based data integration Parameters Which Description Logic for the ontology We will mention different possibilites Which language for user queries Unions of conjunctive queries Which type of mapping We will consider mappings of type GAV Which sources Relational sources

4. 4Ontology-based data integration OWL-DL OWL concept constructors:

5. 5Ontology-based data integration OWL-DL Types of axioms:

6. 6Ontology-based data integration The Description Logic DL-lite

7. 7Ontology-based data integration DL-lite

8. 8Ontology-based data integration DL-lite - example Manages

9. 9Ontology-based data integration Dl-lite - semantics

10. 10Ontology-based data integration Results on data complexity

11. 11Ontology-based data integration A note on mappings In Ontology-based integration we have to deal with the “impedence mismatch” problem Sources store data, while instances of concepts and relations in the ontologies are objects The solution is to define a mapping language that allows specifying how to transform data into objects Basic idea: use “Skolem functions” in the head of the mapping Semantics: objects are denoted by “terms” (of exaclty one level of nesting), and different terms are different objects (unique name assumption on terms)

12. 12Ontology-based data integration Mappings: example Three sources on students: s1 uses code for identifying students s3 uses number for identifying s2 stores (incomplete) correspondences between code and number Student(sbc(code)) :- s1(code,dob,addr,city) Student(sbc(code)) :- s2(number,code) Student(sbn(number)) :- s3(number,addr,city), not s2(number,code) LivesIn(sbc(code),c(city)) :-s1(code,dob,addr,city), city is not null LivesIn(sbc(code),c(city3)) :- s1(code,dob,addr,city1), city1 is null, s2(number,code), s3(number,addr,city3), city3 is not null LivesIn(sbc(code),c(city3)) :- not s1(code,dob,addr,city1), s2(number,code), s3(number,addr,city3), city3 is not null LivesIn(sbn(number),c(city)) :- s3(number,address,city), city is not null, not s2(number,code)