Graph Patterns

Graph Patterns

Spanqit uses three classes to represent the SPARQL graph patterns, all of which implement the GraphPattern interface:

• The TriplePattern class represents triple patterns.
• The GraphPatternNotTriple class represents collections of graph patterns.
• The SubSelect class represents a SPARQL sub query.

Graph patterns are created by the more aptly named GraphPatterns class. Use GraphPatterns#tp() to create a TriplePattern instance:

Prefix dc = Spanqit.prefix("dc", iri("http://purl.org/dc/elements/1.1/"));
Variable book = Spanqit.var("book");

TriplePattern triple = GraphPatterns.tp(book, dc.iri("author"), Rdf.literalOf("J.R.R. Tolkien"));
System.out.println(triple.getQueryString());
// ==> ?book dc:author "J.R.R. Tolkien"

A TriplePattern instance can also be created from the has() and isA() shortcut methods of RdfSubject, and be expanded to contain multiple triples with the same subject via predicate-object lists and object lists:

Prefix foaf = Spanqit.prefix("foaf", iri("http://xmlns.com/foaf/0.1/"));
Variable x = Spanqit.var("x"), name = Spanqit.var("name");

TriplePattern triple = x.has(foaf.iri("nick"), Rdf.literalOf("Alice"), Rdf.literalOf("Alice_"))
    .andHas(foaf.iri("name"), name);
System.out.println(triple.getQueryString());
// ===> ?x foaf:nick "Alice_", "Alice" ;
//	   foaf:name ?name .

Three methods in GraphPatterns exist to create GraphPatternNotTriple instances. GraphPatterns#and() creates a group graph pattern, consisting of the GraphPattern instances passed as parameters:

Variable mbox = Spanqit.var("mbox"), x = Spanqit.var("x");
GraphPatternNotTriple groupPattern =
GraphPatterns.and(x.has(foaf.iri("name"), name), x.has(foaf.iri("mbox"), mbox);
System.out.println(groupPattern.getQueryString());
// ==> { ?x foaf:mbox ?mbox . ?x foaf:name ?name }

GraphPatterns#union() creates an alternative graph pattern, taking the union of the provided GraphPattern instances:

Prefix dc10 = Spanqit.prefix("dc10", iri("http://purl.org/dc/elements/1.0/")),
	dc11 = Spanqit.prefix("dc11", iri("http://purl.org/dc/elements/1.1/"));
Variable book = Spanqit.var("book"), title = Spanqit.var("title");

GraphPatternNotTriple union = GraphPatterns.union(book.has(dc10.iri("title"), title),
	book.has(dc11.iri("title"), title);
System.out.println(union.getQueryString());
// ==> { ?book dc10:title ?title } UNION { ?book dc11:title ?title }

GraphPatterns#optional() creates an optional group graph pattern, consisting of the passed in GraphPatterns:

GraphPatternNotTriple optionalPattern = GraphPatterns.optional(GraphPatterns.tp(x, foaf.iri("mbox"), mbox));
System.out.println(optionalPattern.getQueryString());
// ==> OPTIONAL { ?x foaf:mbox ?mbox }

Finally, GraphPatterns#select() creates an instance of a SubSelect, which represents a SPARQL subquery:

SubSelect subQuery = GraphPatterns.select();

Creating Query Constraints >