# Rasqal RDF Query Library

## Dave Beckett

## Overview

Rasqal is a free software / Open Source C library that handles Resource Description Framework (RDF) query syntaxes, query construction and query execution returning result bindings. The supported query languages are SPARQL and RDQL.

Rasqal was designed to work closely with the Redland RDF library but is entirely separate. It is intended to be a portable library working across many POSIX systems (Unix, GNU/Linux, BSDs, OSX, cygwin) win32 and others.

This is a beta quality library - the code is mature but the API is still changing and the SPARQL support is under active development. See the todo list for the current state information. A summary of the changes can be found in the NEWS file, detailed API changes in the release notes and file-by-file changes in the CVS ChangeLog.

Rasqal provides:

- An RDF query construction and access API.
- A query execution engine including constraint expression evaluation.
- A query result binding API.
- Query language support for SPARQL.
- Query language support for RDQL.
- Triple store querying APIs to support running over external RDF graphs.
- No memory leaks.
- roqet standalone RDF query utility program

Rasqal does not provide an RDF API or triple store, but relies on external libraries implementing the triple store API providing matched RDF data originally from a specified content URI. Rasqal ships with triple store implementations using the output of an RDF parser from Raptor and over a Redland indexed triple store. These can be called using the standalone roqet query utility giving a query language identifier and query string to run the query over content described inside the query string (in RDQL, the `FROM` clause).

Rasqal also works inside Redland (0.9.17 or newer) to provide support for query languages, a query API and a result bindings API over graphs stored in Redland.

## Supported Query Languages

### SPARQL Query Language for RDF

Rasqal provides support for the W3C SPARQL Query Language being developed by the W3C RDF Data Access Working Group, as defined in SPARQL Query Language for RDF, W3C Proposed Recommendation 12 November 2007. It currently implements most of the functionality except for `GRAPH`, `UNION` and part of `OPTIONAL`. For detailed information on the implementation state, see the Rasqal todo / bugs list and the Redland issue tracker.

### RDF Data Query Language (RDQL)

Rasqal provides a complete implementation of the RDQL language, as defined in RDQL - A Query Language for RDF, W3C Member Submission 9 January 2004 based on the earlier versions in Jena defined in RDQL RDF Data Query Language and the RDQL Grammar. The Jena RDQL Tutorial gives an introduction on the language. Rasqal currently passes all the Jena RDQL test suite bar a couple. Detail of the status of the RDQL support is given in the Redland issue tracker.

### LAQRS Adds to Querying RDF in SPARQL (LAQRS)

LAQRS is an experimental set of syntax extensions for SPARQL. The syntax and features may change at any time. At present Rasqal provides only parsing and API support for it.

## Installation and Documentation

The public API is described in the librasqal.3 UNIX manual page and in more detail in the API reference. It is demonstrated in the roqet utility program which shows how to call the query engine and operate over the query results. When Rasqal is used inside Redland, the Redland documentation explains how to call the query engine and contains several example programs.

To install Rasqal see the Installation document.

## Sources

The packaged sources are available from http://download.librdf.org/source/ (master site) and also from the SourceForge site. The development GIT sources can also be browsed or checked out at git://git.librdf.org/repositories/rasqal.git

Rasqal requires Raptor 1.4.18 or newer to build and run, which can be downloaded from the same area as the Rasqal source and binaries.

## License

This library is free software / open source software released under the LGPL (GPL) or Apache 2.0 licenses. See LICENSE.html for full details.

## Mailing Lists

The Redland mailing lists discusses the development and use of Rasqal and Redland as well as future plans and announcement of releases.

Copyright (C) 2003-2010 Dave Beckett
Copyright (C) 2003-2005 University of Bristol