1. On the Semantics of R2RML and its Relationship with the Direct Mapping Juan F. Sequeda Research in Bioinformatics and Semantic Web (RiBS) Lab Department of Computer Science, The University of Texas at Austin SQL query Parser What are the formal semantics of R2RML? What is the relationship between R2RML and Direct Mapping? Logical Query Plan Select Logical Query Plan Optimal Logical Query Plan Physical Query Plan Select Physical Query Plan R2RML Mapping Parser Logical Mapping Select Logical Mapping Optimal Logical Mapping Physical Mapping Select Physical Mapping Exploit a well established architecture: query optimization Organization of query optimization is applicable to mappings Example Methodology Declarative Language Logical Perspective Physical Perspective Triple(S,"rdf:type”,O)←SubjectTemplateValueTermMap(SID, T, S), Class(SID, O) Triple(S,P,O)←SubjectMap(TM, SID), PredicateObjectMap(TM, POID), SubjectTemplateValueTermMap (SID, T, S), PredicateConstantValueTermMap(POID, P), ObjectColumnTermMap(POID, T, O) Triple(S,P,O)←SubjectMap(TM, SID), PredicateObjectMap(TM, POID), SubjectTemplateValueTermMap (SID, T, S), PredicateConstantValueTermMap(POID, P), ReferencingObjectTemplate(POID, T, O) R2RML P template P column P constant O template O column O constant S template O template O column O constant O column O constant O template P template P column P constant O template O column O constant S constant O template O column O constant O column O constant O template P template P column P constant O template O column O constant S column O template O column O constant O column O constant O template 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. 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: R2RML core is as expressive as the Direct Mapping if views are allowed as input Relationship between R2RML and Direct Mapping R2RML core Table Triples Local Triples References Triples Problem Statement empnoenamedept 1Bob100 2Alice200 deptnodname 100CS 200EE rdf:type ex:Employee. ex:name “Bob”. ex:name. rdf:type ex:Employee. ex:name “Alice”. ex:name. rdf:type ex:Department. ex:deptName “CS”. rdf:type ex:Department. ex:deptName “EE”. rr:logicalTable [ rr:tableName "emp" ]; rr:subjectMap [ rr:template "http://ex.com/emp/{empno}"; rr:class ex:Employee; ]; rr:predicateObjectMap [ rr:predicate ex:name; rr:objectMap [ rr:column "ename" ]; ]; rr:predicateObjectMap [ rr:predicate ex:department; rr:objectMap [ rr:parentTriplesMap ; rr:joinCondition [ rr:child "dept"; rr:parent "deptno"; ]; ]. rr:logicalTable [ rr:tableName "dept" ]; rr:subjectMap [ rr:template "http://ex.com/dept/{deptno}"; rr:class ex:Department; ]; rr:predicateObjectMap [ rr:predicate ex:deptName; rr:objectMap [ rr:column ”dname" ]; ]. What does this actually mean? Understanding these questions can help support users and build tools. Three types of triples: Table, Local and Reference RDF Term (S, P, O) can be generated from a Template, Constant or Column W3C Recommendations to map Relational Databases to RDF are R2RML (customizable mapping language) and Direct Mapping (default automatic mapping) are the 5e4d76