• Documentation
• Query with Comunica
• Advanced querying
• SPARQL query types

SPARQL query types

The SPARQL 1.1 query specification introduces four query types:

• SELECT: Return matches as a collection of solution bindings.
• CONSTRUCT: Create RDF triples from matches.
• DESCRIBE: Create RDF triples about a resource.
• ASK: Check if at least one match exists.

The SPARQL 1.1 update specification also introduces query types that modify data, but return no output.

This guide shows how to handle these query types from the command line and via a JavaScript application.

1. Command line

Below, the different query type usages are summarized. More information can be found in the command line guide.

1.1. SELECT

The following query retrieves the first 100 triples from DBpedia:

$ comunica-sparql https://fragments.dbpedia.org/2016-04/en \
    "SELECT * WHERE { ?s ?p ?o } LIMIT 100"

As output, a JSON array of bindings for the selected variables will be returned:

[
{"?s":"https://fragments.dbpedia.org/2016-04/en#dataset","?p":"http://www.w3.org/1999/02/22-rdf-syntax-ns#type","?o":"http://rdfs.org/ns/void#datasource"},
{"?s":"https://fragments.dbpedia.org/2016-04/en#dataset","?p":"http://www.w3.org/1999/02/22-rdf-syntax-ns#type","?o":"http://www.w3.org/ns/hydra/core#Collection"},
{"?s":"https://fragments.dbpedia.org/2016-04/en#dataset","?p":"http://www.w3.org/ns/hydra/core#search","?o":"https://fragments.dbpedia.org/2016-04/en#triplePattern"}
...

1.2. CONSTRUCT

Next to SPARQL SELECT queries, it is also possible to execute CONSTRUCT queries to produce RDF triples:

$ comunica-sparql https://fragments.dbpedia.org/2016-04/en \
    "CONSTRUCT WHERE { ?s ?p ?o } LIMIT 100"

<http://0-access.newspaperarchive.com.topcat.switchinc.org/Viewer.aspx?img=8716084> <http://dbpedia.org/property/accessdate> "2010-04-21"^^<http://www.w3.org/2001/XMLSchema#date>;
    <http://dbpedia.org/property/date> "1939-01-02"^^<http://www.w3.org/2001/XMLSchema#date>;
    <http://dbpedia.org/property/format> "PDF";
    <http://dbpedia.org/property/isCitedBy> <http://dbpedia.org/resource/List_of_Attorneys_General_of_Wisconsin>;
    <http://dbpedia.org/property/location> "Sheboygan, Wisconsin";
    <http://dbpedia.org/property/page> "1";
...

1.3. DESCRIBE

Similar to CONSTRUCT, DESCRIBE will output triples that are connected to a given resource by any predicate:

$ comunica-sparql https://fragments.dbpedia.org/2016-04/en \
    "DESCRIBE <http://dbpedia.org/resource/List_of_Attorneys_General_of_Wisconsin>"

<http://dbpedia.org/resource/List_of_Attorneys_General_of_Wisconsin> <http://dbpedia.org/ontology/wikiPageExternalLink> <http://www.legis.state.wi.us/lrb/bb/05bb/695-743.pdf>, <http://www.usgennet.org/usa/wi/state/wihist-2.htm>, <http://caselaw.lp.findlaw.com/scripts/getcase.pl?court=us&navby=title&v1=State+of+Wisconsin>, <http://law.justia.com/codes/wisconsin/>, <http://legalnewsline.com/?s=Wisconsin+attorney+general>, <http://naag.org/naag/attorneys-general/whos-my-ag/wisconsin/brad-schimel.php>, <http://public.findlaw.com/LCsearch.html?restrict=consumer&entry=%22Wisconsin+Attorney+General%22>, <http://www.abajournal.com/search/results/search&keywords=Wisconsin+Attorney+General/>, <http://www.doj.state.wi.us/>, <http://www.doj.state.wi.us/media-center/2015-news-releases>, <http://www.wisbar.org/Pages/default.aspx>;
    <http://dbpedia.org/ontology/wikiPageID> "4945528"^^<http://www.w3.org/2001/XMLSchema#integer>;
    <http://dbpedia.org/ontology/wikiPageLength> "14830"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger>;
    <http://dbpedia.org/ontology/wikiPageOutDegree> "71"^^<http://www.w3.org/2001/XMLSchema#nonNegativeInteger>;
    <http://dbpedia.org/ontology/wikiPageRevisionID> "697541030"^^<http://www.w3.org/2001/XMLSchema#integer>;
...

1.4. ASK

ASK queries will produce a boolean output:

$ comunica-sparql https://fragments.dbpedia.org/2016-04/en \
    "ASK { ?s ?p ?o }"

true

1.5. Update

Update queries will produce no output, unless an error occurs:

$ comunica-sparql https://example.org/file.ttl \
    "INSERT DATA { <ex:s> <ex:p> <ex:o> }"

2. Application

Below, the different query type usages are summarized. More information can be found in the application guide.

1.1. SELECT

The following query retrieves the first 100 triples from DBpedia:

const bindingsStream = await myEngine.queryBindings(`
  SELECT ?s ?p ?o WHERE {
    ?s ?p ?o
  } LIMIT 100`, {
  sources: ['http://fragments.dbpedia.org/2015/en'],
});
bindingsStream.on('data', (binding) => {
    console.log(binding.get('s').value);
    console.log(binding.get('p').value);
    console.log(binding.get('o').value);
});

1.2. CONSTRUCT

Next to SPARQL SELECT queries, it is also possible to execute CONSTRUCT queries to produce RDF triples:

const quadStream = await myEngine.queryQuads(`
  CONSTRUCT WHERE {
    ?s ?p ?o
  } LIMIT 100`, {
  sources: ['http://fragments.dbpedia.org/2015/en'],
});

quadStream.on('data', (quad) => {
    console.log(quad.subject.value);
    console.log(quad.predicate.value);
    console.log(quad.object.value);
    console.log(quad.graph.value);
});

1.3. DESCRIBE

Similar to CONSTRUCT, DESCRIBE will output triples that are connected to a given resource by any predicate:

const quadStream = await myEngine.queryQuads(`
  DESCRIBE <http://dbpedia.org/resource/List_of_Attorneys_General_of_Wisconsin>`, {
  sources: ['http://fragments.dbpedia.org/2015/en'],
});

quadStream.on('data', (quad) => {
    console.log(quad.subject.value);
    console.log(quad.predicate.value);
    console.log(quad.object.value);
    console.log(quad.graph.value);
});

1.4. ASK

ASK queries will produce a boolean output:

const hasMatches = await myEngine.queryBoolean(`
  ASK {
    ?s ?p <http://dbpedia.org/resource/Belgium>
  }`, {
  sources: ['http://fragments.dbpedia.org/2015/en'],
})

1.5. Update

Update queries will produce a void output:

await myEngine.queryVoid(`
  PREFIX dc: <http://purl.org/dc/elements/1.1/>
  INSERT DATA
  { 
    <http://example/book1> dc:title "A new book" ;
                           dc:creator "A.N.Other" .
  }`, {
  sources: [ store ],
});