de.fuberlin.wiwiss.d2rq.algebra

Class TripleRelation

java.lang.Object

de.fuberlin.wiwiss.d2rq.algebra.NodeRelation

de.fuberlin.wiwiss.d2rq.algebra.TripleRelation

public class TripleRelation
extends NodeRelation

A collection of virtual triples obtained by applying a Relation to a database, and applying NodeMakers for subject, predicate and object to each result row. This is implemented as a stateless wrapper around a NodeRelation.

Author:

Chris Bizer chris@bizer.de, Richard Cyganiak (richard@cyganiak.de)

Field Summary

Fields

Modifier and Type	Field and Description
static Var	OBJECT
static Var	PREDICATE
static Var	SUBJECT

Fields inherited from class de.fuberlin.wiwiss.d2rq.algebra.NodeRelation

TRUE

Constructor Summary

Constructors

Constructor and Description
TripleRelation(Relation baseRelation, NodeMaker subjectMaker, NodeMaker predicateMaker, NodeMaker objectMaker)

Method Summary

Methods

Modifier and Type	Method and Description
TripleRelation	limit(int limit)
TripleRelation	orderBy(Var variable, boolean ascending)
TripleRelation	selectTriple(Triple t)
TripleRelation	selectWithVariables(Triple t) Creates a NodeRelation by applying a triple pattern to the TripleRelation.

Methods inherited from class de.fuberlin.wiwiss.d2rq.algebra.NodeRelation

baseRelation, empty, extendWith, nodeMaker, renameSingleRelation, select, toString, variables, withPrefix

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, wait, wait, wait

Field Detail

SUBJECT

public static final Var SUBJECT

PREDICATE

public static final Var PREDICATE

OBJECT

public static final Var OBJECT

Constructor Detail

TripleRelation

public TripleRelation(Relation baseRelation,
              NodeMaker subjectMaker,
              NodeMaker predicateMaker,
              NodeMaker objectMaker)

Method Detail

orderBy

public TripleRelation orderBy(Var variable,
                     boolean ascending)

Overrides:

orderBy in class NodeRelation

limit

public TripleRelation limit(int limit)

Overrides:

limit in class NodeRelation

selectTriple

public TripleRelation selectTriple(Triple t)

selectWithVariables

public TripleRelation selectWithVariables(Triple t)

Creates a NodeRelation by applying a triple pattern to the TripleRelation. If the triple contains variables, then the variables will be bound to the corresponding values in the resulting NodeRelation. Node.ANY will be converted to a variable "subject", "predicate", "object" depending on its position in the triple pattern. For example, selecting (?x :name ?name) would produce a NodeRelation with ?x bound to the subjects and ?name bound to the objects of this TripleRelation. TODO This is never called at the moment. Why!?

Parameters:

t - A triple pattern involving variables

Returns:

A NodeRelation over the variables occurring in the triple pattern