clj-r2rml

Implementation of 'R2RML: RDB to RDF Mapping Language' W3C proposal for mapping relational databases into RDF in the Clojure programming language. It covers:

• support for custom mappings
• support for the default direct mapping as described in 'A Direct Mapping of Relational Data to RDF'

Relevant W3C document URIs:

http://www.w3.org/TR/2010/WD-r2rml-20101028/ http://www.w3.org/TR/2010/WD-rdb-direct-mapping-20101118/

The current implementation is MySQL centered.

Usage

To create a mapping use Clojure maps describing the RDF triples in the mapping. For example the mapping:

{:logical-table "select concat('_:Department',deptno) AS deptid, deptno, dname, loc from Dept" :class "xyz:dept" :table-graph-iri "xyz:DeptGraph" :subject-map {:column "deptid"} :property-object-map [{:property "dept:deptno" :column "deptno" :datatype "xsd:positiveInteger"} {:property "dept:name" :column "dname"} {:property "dept:location" :column "loc"} {:property "dept:COMPANY" :constant-value "XYZ Corporation"}]}

is equivalent to the following mapping expressed using the Turtle RDF syntax:

<#TriplesMap1> a rr:TriplesMap; rr:logicalTable " Select (':Department' || deptno) AS deptid , deptno , dname , loc from dept "; rr:class xyz:dept; rr:tableGraphIRI xyz:DeptGraph; rr:subjectMap [ a rr:BlankNodeMap; rr:column "deptid"; rr:InverseExpression "{alias.}deptno = substr({alias.}deptid,length(':Department')+1)"]; rr:propertyObjectMap [ rr:property dept:deptno; rr:column "deptno"; rr:datatype xsd:positiveInteger ]; rr:propertyObjectMap [ rr:property dept:name; rr:column "dname" ]; rr:propertyObjectMap [ rr:property dept:location; rr:column "loc" ]; rr:propertyObjectMap [ rr:property dept:COMPANY; rr:constantValue "XYZ Corporation" ]; .

To run the mapping over some relational data, you need to create a mapping context containing a DB connection and call the run-mapping function, the resulting triples will be stored in the :results key of the context:

(def context (make-context db-spec {})) (def res (:results (run-mapping clj-r2rml.core/test-spec context {})))

The result will be stored in Quad records, containing a subject, a predicate, an object and a graph value. The object can containg a Literal record with value, datatype, and language. For the previous table with the following tuples:

Column Name Column Datatype Column Key Constraints deptno INTEGER UNIQUE dname VARCHAR(30) loc VARCHAR(100)

deptno dname loc 10 APPSERVER NEW YORK

The following triples are the generated in this case:

(#:clj-r2rml.core.Quad{:subject ":Department10", :predicate "dept:deptno", :object #:clj-r2rml.core.Literal{:value "10", :datatype "xsd:positiveInteger", :language nil}, :graph "xyz:DeptGraph"} #:clj-r2rml.core.Quad{:subject ":Department10", :predicate "dept:name", :object #:clj-r2rml.core.Literal{:value "APPSERVER", :datatype nil, :language nil}, :graph "xyz:DeptGraph"} #:clj-r2rml.core.Quad{:subject ":Department10", :predicate "dept:location", :object #:clj-r2rml.core.Literal{:value "NEW YORK", :datatype nil, :language nil}, :graph "xyz:DeptGraph"} #:clj-r2rml.core.Quad{:subject ":Department10", :predicate "dept:COMPANY", :object #:clj-r2rml.core.Literal{:value "XYZ Corporation", :datatype nil, :language nil}, :graph "xyz:DeptGraph"} #:clj-r2rml.core.Quad{:subject "_:Department10", :predicate "rdf:type", :object "xyz:dept", :graph "xyz:DeptGraph"})

The default mapping can be applied using the default-mapping-triples function, providing a default namespace for the triples, a map of virtual tables and a context containing a database connection:

(default-mapping-triples "http://clj-r2rml.test" {"Dept" "select * from Dept"} context)

The generated triples in this case are the following:

(#:clj-r2rml.core.Quad{:subject ":0", :predicate "http://clj-r2rml.test/Dept#deptno", :object #:clj-r2rml.core.Literal{:value "10", :datatype "http://www.w3.org/TR/xmlschema-2/#integer", :language nil}, :graph nil} #:clj-r2rml.core.Quad{:subject ":0", :predicate "http://clj-r2rml.test/Dept#dname", :object #:clj-r2rml.core.Literal{:value "APPSERVER", :datatype nil, :language nil}, :graph nil} #:clj-r2rml.core.Quad{:subject ":0", :predicate "http://clj-r2rml.test/Dept#loc", :object #:clj-r2rml.core.Literal{:value "NEW YORK", :datatype nil, :language nil}, :graph nil} #:clj-r2rml.core.Quad{:subject ":0", :predicate "rdf:type", :object "http://clj-r2rml.test/Dept", :graph nil})

A collection of Quad records can be transformed into RDF in the turtle format using the to-rdf function.

Installation

Generate a jar using leiningen and add it to the dependencies of your project. Not in clojars yet.

License

Copyright (C) 2010 Antonio Garrote

Deistributed under the LGPL license