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).
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:
- Any fragment of the dataset you want to query, in this case DBpedia. More datasets.
- A file with the query you want to execute (this can also be a string).
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); });
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
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
.
To install from the latest GitHub sources, execute:
$ git clone [email protected]: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.
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
Support for client-side processing of GeoSPARQL functions is written by Christophe Debruyne. Install this branch from source for GeoSPARQL support. The queries-osi
folder contains several example queries for OSi's Triple Pattern Fragment, available at http://vma01.adaptcentre.ie/. For instance, to obtain labels of of Irish counties that touch at the border, run:
$ bin/ldf-client http://vma01.adaptcentre.ie/boundaries-default queries-osi/irish-counties-touching-labels.sparql
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.