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Named Graphs

Named graphs are supported simply in the Rdf Store in a few ways. RDF4J supports sending contexts as each triple is saved.

Simple Named Graph Load and Query

Here is a very simple example of using the API to Insert data in named graphs and querying with Sparql

First we will define a Trig document to load Trig document

@prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> .
@prefix xsd: <http://www.w3.org/2001/XMLSchema#> .
@prefix swp: <http://www.w3.org/2004/03/trix/swp-1/> .
@prefix dc: <http://purl.org/dc/elements/1.1/> .
@prefix ex: <http://www.example.org/vocabulary#> .
@prefix : <http://www.example.org/exampleDocument#> .
:G1 { :Monica ex:name "Monica Murphy" .
      :Monica ex:homepage <http://www.monicamurphy.org> .
      :Monica ex:email <mailto:monica@monicamurphy.org> .
      :Monica ex:hasSkill ex:Management }

:G2 { :Monica rdf:type ex:Person .
      :Monica ex:hasSkill ex:Programming }

:G4 { :Phobe ex:name "Phobe Buffet" }

:G3 { :G1 swp:assertedBy _:w1 .
      _:w1 swp:authority :Chris .
      _:w1 dc:date "2003-10-02"^^xsd:date .
      :G2 swp:quotedBy _:w2 .
      :G4 swp:assertedBy _:w2 .
      _:w2 dc:date "2003-09-03"^^xsd:date .
      _:w2 swp:authority :Tom .
      :Chris rdf:type ex:Person .
      :Chris ex:email <mailto:chris@bizer.de>.
      :Tom rdf:type ex:Person .
      :Tom ex:email <mailto:tom@bizer.de>}

We will assume that this file is saved on your classpath somewhere at <TRIG_FILE>

Load data through API:

InputStream stream = Thread.currentThread().getContextClassLoader().getResourceAsStream("namedgraphs.trig");
RepositoryConnection conn = repository.getConnection();
conn.add(stream, "", RDFFormat.TRIG);
conn.commit();

Now that the data is loaded we can easily query it. For example, we will query to find what hasSkill is defined in graph G2, and relate that to someone defined in G1.

Query:

PREFIX  ex:  <http://www.example.org/exampleDocument#>
PREFIX  voc:  <http://www.example.org/vocabulary#>
PREFIX  foaf:  <http://xmlns.com/foaf/0.1/>
PREFIX  rdfs:  <http://www.w3.org/2000/01/rdf-schema#>

SELECT *
WHERE
{
  GRAPH ex:G1
  {
    ?m voc:name ?name ;
       voc:homepage ?hp .
  } .
 GRAPH ex:G2
  {
    ?m voc:hasSkill ?skill .
  } .
}

Results:

[hp=http://www.monicamurphy.org;m=http://www.example.org/exampleDocument#Monica;skill=http://www.example.org/vocabulary#Programming;name="Monica Murphy"]

Here is the Query Plan as well:

QueryRoot
   Projection
      ProjectionElemList
         ProjectionElem "m"
         ProjectionElem "name"
         ProjectionElem "hp"
         ProjectionElem "skill"
      Join
         Join
            StatementPattern FROM NAMED CONTEXT
               Var (name=m)
               Var (name=_const_2, value=http://www.example.org/vocabulary#name, anonymous)
               Var (name=name)
               Var (name=_const_1, value=http://www.example.org/exampleDocument#G1, anonymous)
            StatementPattern FROM NAMED CONTEXT
               Var (name=m)
               Var (name=_const_3, value=http://www.example.org/vocabulary#homepage, anonymous)
               Var (name=hp)
               Var (name=_const_1, value=http://www.example.org/exampleDocument#G1, anonymous)
         StatementPattern FROM NAMED CONTEXT
            Var (name=m)
            Var (name=_const_5, value=http://www.example.org/vocabulary#hasSkill, anonymous)
            Var (name=skill)
            Var (name=_const_4, value=http://www.example.org/exampleDocument#G2, anonymous)

Inserting named graph data through Sparql

The new Sparql update standard provides another way to insert data, even into named graphs.

First the insert update:

PREFIX dc: <http://purl.org/dc/elements/1.1/>
PREFIX ex: <http://example/addresses#>
INSERT DATA
{
    GRAPH ex:G1 {
        <http://example/book3> dc:title    "A new book" ;
                               dc:creator  "A.N.Other" .
    }
}

To perform this update, it requires different code than querying the data directly:

Update update = conn.prepareUpdate(QueryLanguage.SPARQL, insert);
update.execute();