1 Models for Information Integration: Tuning Local-as-view into Global-as-view Andrea Cali Giuseppe De Giacomo Maurizio Lenzerini

2 Local-as-view (LAV) vs. Global-as-view (GAV) zSpecifying the mapping between the global schema and the sources zProcessing queries expressed on the global schema zMaintenance

3 Problem zCan we transform a data integration system built with the LAV approach into an equivalent system following a GAV approach? LAV GAV equivalent transformation

4 Framework for Information Integration zDefinition 1. A data integration system I is a triple (G, S, M) yG : Global schema yS : Source schema yM : Mapping between G and S

5 From LAV to GAV zDefinition 2. Let I = be an integration system, having A G as the alphabet of the global schema. An integration system I’ on S is query equivalent to I if for every query q using only the symbols in A G, and for every source databases D: zQuery equivalent transformation (I and I’) yQuery alphabet yQuery answer

6 LAV System LAV

7 GAV System after Transformation

8 Example zLAV System I(G,S,M) yG: cites/2, sameTopic/2 yS: source1, source2 yM: xp(source1) = { |cites(X,Y) & cites(Y,X)} xp(source2) = { |sameTopic(X,Y)&cites(X,Z)&cites(Y,W)} zGAV System I’(G’,S,M’)

9 Example (Cont.) zGAV System I’(G’,S,M’) yG’: xRelations: cites/2, sameTopic/2, sourceImage1/2, sourceImage2/2, sourceImageExp1/2, sourceImageExp2/4 xInclusion dependencies: sourceImage1[1,2]  sourceImageExp1[1,2] sourceImage2[1,2]  sourceImageExp2[1,2] sourceImageExp1[1,2]  cites[1,2] sourceImageExp1[2,1]  cites[1,2] sourceImageExp2[1,3]  cites[1,2] sourceImageExp2[2,4]  cites[1,2] sourceImageExp2[1,2]  sameTopic[1,2] yM’ xp’(sourceImage1) = { |source1(X,Y)} xp’(sourceImage2) = { |source2(X,Y)}

10 Conclusion zStudy the relative expressive power of LAV and GAV approaches to data integration zTransform a LAV system into a GAV system yThe global schema is expressed in the relational model with inclusion dependencies yQueries used are expressed in the language of conjunctive queries