# Rasqal RDF Query Library

## Dave Beckett

## Overview

Rasqal is a free software / Open Source C library that handles Resource Description Framework (RDF) query language syntaxes, query construction and execution of queries returning results as bindings, boolean, RDF graphs/triples or syntaxes. The supported query languages are SPARQL 1.0, RDQL (will be removed in 0.9.30), SPARQL Query 1.1, SPARQL Update 1.1 (no executing) and the Experimental SPARQL extensions (LAQRS). Rasqal can write binding query results in the SPARQL XML, SPARQL JSON, CSV, TSV, HTML, ASCII tables, RDF/XML and Turtle / N3 and read them in SPARQL XML, RDF/XML and Turtle / N3.

Rasqal was designed to work closely with the Redland RDF library and the Raptor[2] RDF Syntax Library but is entirely separate from both.

This is a beta quality library - the code is mature, the API is mostly stable but changing slowly. Rasqal supports all of SPARQL 1.0 query and most of SPARQL 1.1 query. It is a portable library and has been tested on multiple POSIX systems and architectures. Rasqal has no known memory leaks.

A summary of the changes can be found in the NEWS file and detailed API changes in the release notes.

Rasqal provides:

- An RDF query construction and access API.
- Query language support for SPARQL 1.0 Query.
- Query language support for most of draft SPARQL 1.1 Query.
- Query language support for RDQL. RDQL support will be withdrawn in Rasqal 0.9.30
- A query execution engine executing sub-queries, aggregate expressions and grouping.
- The complete SPARQL 1.1 (draft) built-in function and operator library
- A query result binding API.
- Query result bindings formatting into SPARQL XML, SPARQL JSON, CSV, TSV, HTML, ASCII tables, RDF/XML, Turtle / N3 and from SPARQL XML, RDF/XML and Turtle / N3.
- Triple store querying APIs to support running over external RDF graphs.
- No memory leaks.
- roqet standalone command line RDF query utility program

Known bugs and issues are recorded in the Redland issue tracker.

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 a triple store implementation using the output of an RDF parser from Raptor. This can be called using the standalone command line roqet query utility giving a query language identifier (default sparql), the query string and optionally the data to use unless it is declared in the query string.

Rasqal is used inside Redland to provide support for query languages, a query API and a result bindings API over graphs stored in indexed Redland triple stores. Since this can index the triples it will be faster than the default rasqal triple store of reading the triples from Raptor into memory when the queries are complex.

## Supported Query Languages

### SPARQL Query Language for RDF

Rasqal provides complete support for the W3C SPARQL Query Language 1.0 developed by the W3C RDF Data Access Working Group, as defined in SPARQL Query Language for RDF, W3C Recommendation 15 January 2008.

Rasqal implements most of the SPARQL 1.1 Query and SPARQL 1.1 Update W3C Working Drafts of 05 January 2012 including aggregates, subqueries, expression in SELECT, assignment, short form for `CONSTRUCT` and all the new set of builtin functions and operators. Property Paths are likely never be supported since it is a lot of internal work and new APIs needed.

The details on the Rasqal support for SPARQL 1.1 can be found at the rasqal testing SPARQL 1.1 page which shows the SPARQL 1.1 tests that fail and any diagnosis.

### RDF Data Query Language (RDQL)

RDQL support will be withdrawn in Rasqal 0.9.30

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. 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 parsing and API support for alternate update syntaxes, the `EXPLAIN` keyword, plus executing a few experimental extension functions: `NOW()` / `CURRENT_DATETIME()`, `FROM_UNIXTIME()` and `TO_UNIXTIME()`.

## Installation and Documentation

The public API is described 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 build and install Rasqal from sources 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 on GitHub or checked out at git://github.com/dajobe/rasqal.git

Rasqal requires Raptor 2.0.7 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) 2003-2012 Dave Beckett
Copyright (C) 2003-2005 University of Bristol