Linked Data Fragments Client

On today's Web, Linked Data is published in different ways, including data dumps, subject pages, and results of SPARQL queries. We call each such part a Linked Data Fragment of the dataset.

The issue with the current Linked Data Fragments is that they are either so powerful that their servers suffer from low availability rates (as is the case with SPARQL), or either don't allow efficient querying.

Instead, this client solves queries by accessing Triple Pattern Fragments.
Each Triple Pattern Fragment offers:

• data that corresponds to a triple pattern (example).
• metadata that consists of the (approximate) total triple count (example).
• controls that lead to all other fragments of the same dataset (example).

Execute SPARQL queries

You can execute SPARQL queries against Triple Pattern Fragments like this:

$ ldf-client http://fragments.dbpedia.org/2015/en query.sparql

The arguments to the ldf-client command are:

1. Any fragment of the dataset you want to query, in this case DBpedia. More datasets.
2. A file with the query you want to execute (this can also be a string).

From within your application

First, create a FragmentsClient to fetch fragments of a certain dataset.
Then create a SparqlIterator to evaluate SPARQL queries on that dataset.

var ldf = require('ldf-client');
var fragmentsClient = new ldf.FragmentsClient('http://fragments.dbpedia.org/2015/en');
 
var query = 'SELECT * { ?s ?p <http://dbpedia.org/resource/Belgium>. ?s ?p ?o } LIMIT 100',
    results = new ldf.SparqlIterator(query, { fragmentsClient: fragmentsClient });
results.on('data', function (result) { console.log(result); });

Install the client

The command-line client requires Node.js 4.0 or higher and is tested on OSX and Linux. To install, execute:

$ [sudo] npm install -g ldf-client

Browser version

The client can also run in Web browsers via browserify, which provides browser equivalents for Node.js-specific parts. Try the live demo.

To build a browserified version, run:

npm install [-g] browserify
npm run browserify

The browserified version will be written to ldf-client-browser.js.

The API is the same as that of the Node version, except that ldf = require('ldf-client') is no longer necessary, since ldf is exposed as window.ldf.

From source

To install from the latest GitHub sources, execute:

$ git clone git@github.com:LinkedDataFragments/Client.js
$ cd Client.js
$ npm install .

Then run the application with:

$ bin/ldf-client http://fragments.dbpedia.org/2015/en queries/artists-york.sparql

The queries folder contains several example queries for DBpedia.

(Optional) Running in a Docker container

If you want to rapidly deploy use the client as a microservice, you can build a Docker container as follows:

$ docker build -t ldf-client .

After that, you can run your newly created container:

$ docker run -it --rm ldf-client http://fragments.dbpedia.org/2015/en 'SELECT * WHERE { ?s ?p ?o } LIMIT 100'

Mounting custom config and query files can be done like this:

$ docker run -it --rm $(pwd)/config.json:/tmp/config.json $(pwd)/query.sparql:/tmp/query.sparql ldf-client http://fragments.dbpedia.org/2015/en -f /tmp/query.sparql -c /tmp/config.json

License

The Linked Data Fragments client is written by Ruben Verborgh and colleagues.

This code is copyrighted by Ghent University – imec and released under the MIT license.