RDF in-memory quad store implementation using PDO and SQLite.

1.0 2021-04-12 06:42 UTC

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Last update: 2023-01-06 12:22:00 UTC


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RDF in-memory quad store implementation using PDO and SQLite.


To install this library use Composer via:

composer require sweetrdf/in-memory-store-sqlite


Use InMemoryStoreSqlite::createInstance() to get a ready-to-use store instance (see example below). Sending SPARQL queries can be done via query method. Your data is stored inside an in-memory SQLite database file. After the script ends all your data inside the store will be gone.


Example 1 (First steps)

Create a store instance, load a few triples into it and run a query.

use sweetrdf\InMemoryStoreSqlite\Store\InMemoryStoreSqlite;

// get ready to use store instance
$store = InMemoryStoreSqlite::createInstance();

// send a SPARQL query which creates two triples
$store->query('INSERT INTO <http://example.com/> {
    <http://s> <http://p1> "baz" .
    <http://s> <http://xmlns.com/foaf/0.1/name> "label1" .

// send another SPARQL query asking for all triples
$res = $store->query('SELECT * WHERE {?s ?p ?o.}');
$triples = $res['result']['rows'];
echo \count($triples); // outputs: 2
// $triples contains result set, which consists of arrays and scalar values

Example 2 (Consume SPARQL client result)

Use sweetrdf/sparql-client and a PSR-7-compatible library (like guzzlehttp/guzzle) to query a SPARQL endpoint. For now you have to "transform" SPARQL result set to a quad-list manually. Afterwards add quads to store and query it. Check test testSparqlClientCompatibility in InMemoryStoreSqliteTest.php for a working example.

use GuzzleHttp\Client;
use GuzzleHttp\Psr7\Request;
use simpleRdf\Connection;
use simpleRdf\DataFactory;

 * get data from a SPARQL endpoint
$httpClient = new Client();
$dataFactory = new DataFactory();
$connection = new Connection($httpClient, $dataFactory);
$query = 'SELECT * WHERE {?s ?p ?o} limit 5';
// set SPARQL endpoint URL
$url = 'https://arche-sparql.acdh-dev.oeaw.ac.at/sparql?query=';
$query = new Request('GET', $url.rawurlencode($query));
$statement = $connection->query($query);

 * add result to the store
$quads = [];
foreach ($statement as $entry) {
    // $entry is an object; s, p and o are variables from your query
    $quads[] = $dataFactory->quad($entry->s, $entry->p, $entry->o);
$store = InMemoryStoreSqlite::createInstance();

// send query and check result
$result = $store->query('SELECT * WHERE {?s ?p ?o.}');
echo count($result['result']['rows']); // outputs 5

SPARQL support

Store supports a lot of SPARQL 1.0/1.1 features. For more information please read SPARQL-support.md.


Store uses an in-memory SQLite file configured with:

  • PRAGMA synchronous = OFF
  • PRAGMA journal_mode = OFF
  • PRAGMA locking_mode = EXCLUSIVE
  • PRAGMA page_size = 4096

Check PDOSQLiteAdapter.php for more information.

When adding several hundred or more triples at once you may experience increased execution time. Local tests showed that per second around 1500 triples can be added.


This work is licensed under the terms of the GPL 3 or later.


This work is based on the code of ARC2 from https://github.com/semsol/arc2 (by Benjamin Nowak and contributors). To see what was extracted check pull request #1. ARC2 is dual licensed under the terms of GPL 2 (or later) as well as W3C Software License.