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SPARQL 1.1 Query: Results

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http://opendatacommunities.org/id/geography/administration/md/E08000012 http://www.w3.org/1999/02/22-rdf-syntax-ns#type geosparql: Geometry
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SPARQL API: The Basics

The most flexible way to access the data is by using SPARQL, a query language, analagous to SQL for relational databases, for retrieving and manipulating data from graph databases like ours. We support SPARQL 1.1 query syntax. Many online tutorials are available.

To submit a SPARQL query from your code, you issue an HTTP GET or POST to our endpoint:http://opendatacommunities.org/sparql, with the query itself as a url-encoded parameter called query.

For example, to run the following simple SPARQL query and get the results as JSON:

SELECT * WHERE {?s ?p ?o} LIMIT 10

Option 1: POST (recommended)

Issue a POST to the endpoint, with the query in the body, and an Accept header of sparql-results+json:

POST http://opendatacommunities.org/sparql HTTP/1.1
Host: opendatacommunities.org
Accept: application/sparql-results+json
Content-Type: application/x-www-form-urlencoded

query=SELECT+%2A+WHERE+%7B%3Fs+%3Fp+%3Fo%7D+LIMIT+10

Option 2: GET

Issue a GET to the following URL (note the .json extension - see the formats section for more detail on this):

GET http://opendatacommunities.org/sparql.json?query=SELECT+%2A+WHERE+%7B%3Fs+%3Fp+%3Fo%7D+LIMIT+10

Scroll down to the end of this page for examples of both of these methods in a few different languages.

Results formats

As with other aspects of our API, to get the data in different formats, you can use either (a) a format extension or (b) an HTTP Accept header. Available result formats depend on the type of SPARQL query. There are four main forms:

SELECT queries return tabular results, and the formats available reflect this:

Format Extensions Accept Headers
XML .xml application/xml,
application/sparql-results+xml
JSON .json application/json,
application/sparql-results+json
Text .txt, .text text/plain
CSV .csv text/csv

CONSTRUCT and DESCRIBE queries return graph data, so the results are available in the same formats as our resource APIs:

Format Extensions Accept Headers
RDF/XML .rdf application/rdf+xml
N-triples .nt, .txt, .text application/n-triples,
text/plain
Turtle .ttl text/turtle
JSON-LD .json application/ld+json,
application/json

ASK queries return a boolean result:

Format Extensions Accept Headers
XML .xml application/xml,
application/sparql-results+xml
JSON .json application/json,
application/sparql-results+json
Text .txt, .text text/plain
Results pagination

We accept page and per_page parameters for paginating the results of SELECT queries (we automatically modify your query to apply LIMIT and OFFSET clauses). For other query types (i.e. DESCRIBE, CONSTRUCT, ASK), pagination like this doesn’t make so much sense, so these parameters are ignored.

For requests made through the website (i.e. HTML format), the page size is defaulted to 20. For requests to our sparql endpoint for data formats (i.e. non-HTML), there will be no defaults for these parameters (i.e. results are unlimited. For performance reasons we generally advise LIMITing your query if possible).

Parameter Substitution

You can parameterise your SPARQL by including %{tokens} in your queries, and providing values for the tokens in the request parameters.

Note that the following tokens are reserved and cannot be used as parameters for substitution:

  • controller
  • action
  • page
  • per_page
  • id
  • commit
  • utf8
  • query
Cross Origin Resource Sharing

Our servers are configured to allow access from all domains. This means that if you’re writing JavaScript to request data from our server in to a web page hosted on another domain, your browser should check this header and allow it.

If you need to support very old browsers, you can additionally pass a callback parameter and the results will be wrapped in that function. For example:

http://opendatacommunities.org/sparql.json?callback=myCallbackFunction&query=SELECT+%2A+WHERE+%7B%3Fs+%3Fp+%3Fo%7D+LIMIT+10

This help topic on the jQuery website has more details.

Examples

Using cURL

Here’s a couple of examples running a query using the widely available cURL command line program.

Request the results as XML, using a POST:

curl -X POST -H "Accept: application/sparql-results+xml" -d "query=SELECT%20*%20WHERE%20%7B%3Fs%20%3Fp%20%3Fo%7D%20LIMIT%2010" http://opendatacommunities.org/sparql

Request the results as JSON, using a GET:

curl -X GET -H "Accept: application/sparql-results+json" http://opendatacommunities.org/sparql?query=SELECT%20*%20WHERE%20%7B%3Fs%20%3Fp%20%3Fo%7D%20LIMIT%2010

Using JavaScript

This example HTML page uses jQuery to issue a POST to our SPARQL endpoint, requesting the results as JSON.

<!DOCTYPE html>
<html>
<head>
	<script src='http://code.jquery.com/jquery-1.9.1.min.js'></script>
</head>
<body>
<script type='text/javascript'>

	var query = 'SELECT * WHERE {?s ?p ?o} LIMIT 10';
	var url = 'http://opendatacommunities.org/sparql.json';
	$.ajax({
		method: 'POST',
		dataType: 'json',
		url: url,
		data: {query: query},
		success: function(data) {
			alert('success: ' + data.results.bindings.length + ' results');
			console.log(data);
		}
	});
</script>
</body>
</html>