Author: jpz6311whu
Date: Sun Aug 16 23:36:58 2015
New Revision: 1696184
URL: http://svn.apache.org/r1696184
Log:
compose doc for construct-quad.mdtext
Modified:
jena/site/trunk/content/documentation/query/construct-quad.mdtext
Modified: jena/site/trunk/content/documentation/query/construct-quad.mdtext
URL:
http://svn.apache.org/viewvc/jena/site/trunk/content/documentation/query/construct-quad.mdtext?rev=1696184&r1=1696183&r2=1696184&view=diff
==============================================================================
--- jena/site/trunk/content/documentation/query/construct-quad.mdtext (original)
+++ jena/site/trunk/content/documentation/query/construct-quad.mdtext Sun Aug
16 23:36:58 2015
@@ -1,2 +1,97 @@
-Title: ARQ - Construct Quad
+# ARQ - Construct Quad
+
+## Introduction
+The current W3C recommendation of [SPARQL
1.1](http://www.w3.org/TR/sparql11-query/) supports the CONSTRUCT query form,
which returns a single RDF graph specified by a graph template.
+The result is an RDF graph formed by taking each query solution in the
solution sequence, substituting for the variables in the graph template, and
combining the triples into a single RDF graph by set union.
+However, it does not directly generate quads or [RDF
datasets](http://www.w3.org/TR/sparql11-query/#rdfDataset).
+In order to eliminate this limitation, Jena ARQ extends the grammar of the
CONSTRUCT query form and provides the according components, which brings more
conveniences for the users manipulating RDF datasets with SPARQL.
+
+## Query Syntax
+
+A CONSTRUST template of the SPARQL 1.1 query String is
[Turtle](http://www.w3.org/TR/turtle/) format with possible variables.
+The syntax for this extension follows that style in ARQ, using
[TriG](http://www.w3.org/TR/trig/) plus variables.
+Just like SPARQL 1.1, there're 2 forms for ARQ Contruct Quad query String:
+
+### Complete Form
+
+ CONSTRUCT {
+ # Named graph
+ GRAPH :g { ?s :p ?o }
+ # Default graph
+ { ?s :p ?o }
+ # Named graph
+ ?g { :s ?p :o }
+ # Default graph
+ :s ?p :o
+ } WHERE {
+ # SPARQL 1.1 WHERE Clause
+ ...
+ }
+
+The default graphs and the named graphs can be constructed within the
CONSTRUCT clause in the above way.
+Note that, for constructing the named graph, the token of GRAPH can be
optional.
+The brackets of the triples to be constructed in the default graph can also be
optional.
+
+### Short Form
+
+ CONSTRUCT WHERE {
+ # Basic dataset pattern (only the default graph and the named graphs)
+ ...
+ }
+
+A short form is provided for the case where the template and the pattern are
the same and the pattern is just a basic dataset pattern (no FILTERs and no
complex graph patterns are allowed in the short form). The keyword WHERE is
required in the short form.
+
+### Grammar
+
+The normative definition of the syntax grammar of the query string is defined
in this table:
+
+ConstructQuery | ::= 'CONSTRUCT' ( ConstructTemplate DatasetClause*
WhereClause SolutionModifier | DatasetClause* 'WHERE' '{' ConstructQuads '}'
SolutionModifier )
+ConstructTemplate | ::= '{' ConstructQuads '}¡¯
+ConstructQuads | ::= TriplesTemplate? ( ConstructQuadsNotTriples
'.'? TriplesTemplate? )*
+ConstructQuadsNotTriples | ::= ( 'GRAPH' VarOrIri )? '{' TriplesTemplate?
'}'
+TriplesTemplate | ::= TriplesSameSubject ( '.' TriplesTemplate? )?
+DatasetClause, WhereClause, SolutionModifier, TriplesTemplate, VarOrIri,
TriplesSameSubject | [SPARQL 1.1
Grammar](http://www.w3.org/TR/sparql11-query/#grammar)
+
+## Programming API
+
+ARQ provides 2 additional methods in QueryExecution for Construct Quad.
+
+ Iterator<Quad> QueryExecution.execConstructQuads() // allow duplication
+ Dataset QueryExecution.execConstructDataset() // no duplication
+
+One difference of the 2 methods is:
+The method of execConstructQuads() returns an Iterator of Quad, allowing
duplication.
+But execConstructDataset() constructs the desired Dataset object with only
unique Quads.
+
+In order to use these methods, it's required to swtich on the query syntax of
ARQ beforehead, when creating the Query object:
+
+ Query query = QueryFactory.create(queryString, Syntax.syntaxARQ);
+
+If the query is supposed to construct only triples, not quads, the triples
will be constructed in the default graph. For example:
+
+ String queryString = "CONSTRUCT { ?s ?p ?o } WHERE ... "
+ ...
+ Iterator<Quad> quads = qexec.execConstructQuads(); // The graph node of
the quads are the default graph (ARQ uses <urn:x-arq:DefaultGraphNode>).
+
+If the query string stands for constructing quads while the method of
exeConstructTriples() are called,
+it returns only the triples in the default graph of the CONSTRUCT query
template. It's called a "projection" on the default graph. For instance:
+
+ String queryString = "CONSTRUCT { ?s ?p ?o . GRAPH ?g1 { ?s1 ?p1 ?o1 } }
WHERE ..."
+ ...
+ Iterator<Triple> triples = qexec.exeConstructTriples(); // The part of
"GRAPH ?g1 { ?s1 ?p1 ?o1 }" will be ignored. Only "?s ?p ?o" in the default
graph will be returned.
+
+More examples can be found at
jena-arq/src-examples/arq/examples/constructquads/ExampleConstructQuads.java
+
+## Fuseki Support
+
+Jena [Fuseki] is also empowed with Construct Quad query as a built-in
function. No more addtional configuration is required to switch it on.
+Because
[QueryEngineHTTP](http://jena.apache.org/documentation/javadoc/arq/com/hp/hpl/jena/sparql/engine/http/QueryEngineHTTP.html)
is just an implementation of QueryExcecution, there's no much difference for
the client users to manipulate the programming API described in the previous
sections, e.g.
+
+ String queryString = " CONSTRUCT { GRAPH <http://example/ns#g1> {?s ?p ?o}
} WHERE {?s ?p ?o}" ;
+ Query query = QueryFactory.create(queryString, Syntax.syntaxARQ);
+ try ( QueryExecution qExec =
QueryExecutionFactory.sparqlService(serviceQuery, query) ) { // serviceQuery is
the URL of the remote service
+ Iterator<Quad> result = qExec.execConstructQuads();
+ ...
+ }
+ ...
