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SPARQL support

Introduction

This store supports many SPARQL Query Language features (to a certain extent) and also a number of pragmatic extensions such as aggregates (AVG / COUNT / MAX / MIN / SUM) and write mechanisms. The changes to the SPARQL specification were kept at a minimum, so that the existing grammar parser and store functionality can be re-used.

This page documents the core differences between SPARQL and what is called "SPARQL+" (originally from in ARC2).

SELECT

Aggregates

SELECT COUNT(?contact) AS ?contacts WHERE {
  <#me> foaf:knows ?contact .
}
ORDER BY DESC(?contacts)

Note that the alias (... AS ...) has to be specified.

If you have more than a single result variable, you also have to provide GROUP BY information:

SELECT ?who COUNT(?contact) AS ?contacts WHERE {
  ?who foaf:knows ?contact .
}
GROUP BY ?who

Store implementation currently has a bug in the SUM (link) and AVG (link function.

Supported aggregate functions

AVG COUNT MIN MAX SUM
Support x (but bugged) x x x (but bugged)

Supported relational terms

= != < >
Support x x x x

Supported FILTER functions

bound datatype isBlank isIri isLiteral isUri lang langMatches regex str
Support x x x x x x x x x x

INSERT INTO

INSERT INTO <http://example.com/> {
 <#foo> <bar> "baz" .
}

In this INSERT form the triples have to be fully specified, variables are not allowed.

It is possible to dynamically generate the triples that should be inserted:

INSERT INTO <http://example.com/inferred> {
  ?s foaf:knows ?o .
}
WHERE {
  ?s xfn:contact ?o .
}

DELETE

DELETE {
 <#foo> <bar> "baz" .
 <#foo2> <bar2> ?any .
}

Each specified triple will be deleted from the RDF store. It is possible to specify variables as wildcards, but they can't be used to build connected patterns. Each triple is handled as a stand-alone pattern.

FROM can be used to restrict the delete operations to selected graphs. It's also possible to not specify any triples. The whole graph will then be deleted.

DELETE FROM <http://example.com/archive>

DELETE can be combined with a WHERE query, like:

DELETE FROM <http://example.com/inferred> {
  ?s rel:wouldLikeToKnow ?o .
}
WHERE {
  ?s kiss:kissed ?o .
}

Instead of deleting triples only in one graph, you can in all graphs by using:

DELETE {
  ?s rel:wouldLikeToKnow ?o .
}
WHERE {
  ?s kiss:kissed ?o .
}

SPARQL Grammar Changes and Additions

Query ::= Prologue ( SelectQuery | DescribeQuery | AskQuery | InsertQuery | DeleteQuery )

SelectQuery ::= 'SELECT' ( 'DISTINCT' | 'REDUCED' )? ( Aggregate+ | Var+ | '*' ) DatasetClause* WhereClause SolutionModifier

Aggregate ::= ( 'AVG' | 'COUNT' | 'MAX' | 'MIN' | 'SUM' ) '(' Var | '*' ')' 'AS' Var

InsertQuery ::= 'INSERT' 'INTO' IRIref DatasetClause* WhereClause? SolutionModifier

DeleteQuery ::= 'DELETE' ( 'FROM' IRIref )* DatasetClause* WhereClause? SolutionModifier

SolutionModifier ::= GroupClause? OrderClause? LimitOffsetClauses?

GroupClause ::= 'GROUP' 'BY' Var ( ',' Var )*