#DOAP
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
Query 1.0, 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, CSV, TSV, RDF/XML
and Turtle / N3.
Rasqal was designed to work closely with the Redland RDF library and
the Raptor 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 SPARQL 1.1 Query.
* 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 (1.0), W3C Recommendation 15 January
2008.
Rasqal implements most of the SPARQL 1.1 Query Language and SPARQL 1.1
Update W3C Recommendations 21 March 2013 including aggregates,
subqueries, expression in SELECT, assignment, short form for CONSTRUCT
and all the new set of builtin functions and operators.
Unimplemented parts of SPARQL 1.1:
* BIND scope
* VALUES: part of federated query
* Decimal and double canonical format details
* EXISTS / NOT EXISTS
* JSON result format reading
* MINUS
* Property Paths: These are likely never be supported since it is a
lot of work (estimate: 3 months full time) and might need multiple
new APIs to talk to the storage layer.
* SERVICE: Part of federated query
Out of scope parts of SPARQL 1.1:
* Entailment and inference: Rasqal is not an inference engine
* SPARQL Federated Query
* SPARQL Update (also called SPARQL Protocol): The Update syntax is
parsed with parser name 'sparql-update' but nothing is executed
inside Rasqal. Supporting SPARQL Update requires a protocol server
that responds to requests to perform operations on a graph store.
Rasqal is a query library and does not have an event loop or triple
store. Redstore is a system supporting SPARQL Update and Service
Description built with Rasqal by using Redland librdf for graph
storage and query.
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.
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/. 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) 2003-2014 Dave Beckett
Copyright (C) 2003-2005 University of Bristol
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