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Web Access via Query and API

Caliper offers the possibility of querying classifications to extract data on demand. This functionality allows for easy access of classifications and correspondences inside information systems or any other computer application.

SPARQL endpoints and APIs - a (very) brief introduction

RDF data can be stored in triplestores and queried using the SPARQL query language, just like relational data can be stored in relational databases and queried using the SQL query language.

A SPARQL endpoint is a point of presence on the Internet (reachable through an URL), provided by a SPARQL server (triple store accessible from the web), and endowed with a web API. Thanks to its web API, a SPARQL server can receive SPARQL queries encoded as URLs and return the corresponding results. This means that we can compose an URL so as to contain a SPARQL query, and use that URL as a command to get data from a SPARQL endpoint.

The World Wide Web Consortium (W3C) has produced technical specifications for the SPARQL query language and for the SPARQL Protocol (in fact, SPARQL is a recursive acronym, standing for "SPARQL Protocol and RDF Query Language"). The W3C has also produced recommendations for the CSV and TSV formats, the XML format and the JSON format used to return reults from SPARQL queries. Therefore different clients exists to query SPARQL endpoints using different languages, such as Python or Java

Caliper SPARQL endpoints

All classifications have a SPARQL endpoint in Caliper. Since SPARQL endpoints are meant to serve as points of communication between machine applications, when you try accessing the URL of a SPARQL endpoint via browser, you typically receive the error message 404 ("page not found"). However, for the purposes of demostrating the power of having possibilities SPARQL endpoints, we have provided all Caliper SPARQL edpoints with a web interface (powered by YASGUI).

In this way, you can access a Caliper SPARQL endpoint with your browser, place there your query, click the button "run" and see the results. You can also download the results.

Some sample SPARQL queries

We have prepared some queries for your tests.