On the Semantics of R2RML and its Relationship with the Direct Mapping

1. On the Semantics of R2RML and its Relationship with the Direct Mapping Juan F. SequedaResearch in Bioinformatics and Semantic Web (RiBS) Lab Department of Computer Science, The University of Texas at Austin Problem Statement Example W3C Recommendations to map Relational Databases to RDF are R2RML (customizable mapping language) and Direct Mapping (default automatic mapping) are the <emp/1> rdf:typeex:Employee. <emp/1> ex:name “Bob”. <emp/1> ex:name<dept/100>. <emp/2> rdf:typeex:Employee. <emp/2> ex:name“Alice”. <emp/2> ex:name <dept/200>. <dept/100> rdf:typeex:Department. <dept/100> ex:deptName “CS”. <dept/200> rdf:typeex:Department. <dept/200> ex:deptName“EE”. • What are the formal semantics of R2RML? • What is the relationship between R2RML and Direct Mapping? <#TriplesMap1> rr:logicalTable [ rr:tableName"emp" ]; rr:subjectMap [ rr:template "http://ex.com/emp/{empno}"; rr:classex:Employee; ]; rr:predicateObjectMap [ rr:predicateex:name; rr:objectMap [ rr:column "ename" ]; ]; rr:predicateObjectMap [ rr:predicateex:department; rr:objectMap [ rr:parentTriplesMap <#TriplesMap2>; rr:joinCondition [ rr:child "dept"; rr:parent "deptno"; ]; ]; ]. Understanding these questions can help support users and build tools. Methodology • Exploit a well established architecture: query optimization • Organization of query optimization is applicableto mappings What does this actually mean? Declarative Language SQL query R2RML Mapping Parser Parser Logical Perspective <#TriplesMap2> rr:logicalTable [ rr:tableName"dept" ]; rr:subjectMap [ rr:template "http://ex.com/dept/{deptno}"; rr:classex:Department; ]; rr:predicateObjectMap [ rr:predicateex:deptName; rr:objectMap [ rr:column ”dname" ]; ]. Logical Query Plan Logical Mapping Select Logical Query Plan Select Logical Mapping Optimal Logical Mapping Optimal Logical Query Plan Physical Perspective Select Physical Mapping Select Physical Query Plan Physical Query Plan Physical Mapping R2RML Otemplate Otemplate Otemplate Ptemplate Ocolumn Ptemplate Ocolumn Ptemplate Ocolumn Oconstant Oconstant Oconstant Otemplate Otemplate Otemplate Stemplate Pconstant Ocolumn Sconstant Pconstant Ocolumn Scolumn Pconstant Ocolumn Oconstant Oconstant Oconstant Otemplate Otemplate Otemplate Pcolumn Ocolumn Pcolumn Ocolumn Pcolumn Ocolumn Oconstant Oconstant Oconstant RDF Term (S, P, O) can be generated from a Template, Constant or Column Three types of triples: Table, Local and Reference Theorem: The total number of distinct Datalog rules which can be used to generate RDF triples is 57 Proof: 3 rules to generate Table triples, 27 rules to generate Local triples and 27 rules to generate Reference triples. R2RMLcore Relationship between R2RML and Direct Mapping Table Triples • Direct Mapping is the default and automatic approach of generating RDF and OWL from a Relational Database • Semantics formalized in Datalog (see WWW2012 paper) • Hypothesis: R2RMLcoreis as expressive as theDirect Mapping if views are allowed as input Local Triples References Triples 5e4d76