CQL-Java -- a free CQL parser and related tools, for Java

Introduction

CQL-Java is a Free Software project that provides:

• A set of classes for representing a CQL parse tree (a base CQLNode class, CQLBooleanNode and its subclasses, CQLTermNode, etc.)
• A CQLCompiler class (and its lexer) which builds a parse tree given a CQL query as input.
• A selection of compiler back-ends to render out the parse tree as:
  • XCQL (the standard XML representation)
  • CQL (i.e. decompiling the parse-tree)
  • PQF (Yaz-style Prefix Query Format)
  • BER code for the Z39.50 Type-1 query
• A random query generator, useful for testing.

CQL is "Common Query Language", a query language designed under the umbrella of the ZING initiative (Z39.59-International Next Generation). The official specification is at http://www.loc.gov/standards/sru/cql/ and there's more (and friendlier) information at http://zing.z3950.org/cql/index.html

XCQL is "XML CQL", a representation of CQL-equivalent queries in XML which is supposed to be easier to parse. The specification is at http://docs.oasis-open.org/search-ws/searchRetrieve/v1.0/os/schemas/xcql.xsd in the form of an XML Schema.

But if you didn't know that, why are you even reading this? :-)

What's What in this Distribution?

• README.md -- This file
• Changes -- History of releases
• LGPL-2.1 -- The GNU lesser GPL (see below)
• pom.xml -- Maven project file to control compilation.
• src -- Source-code for the CQL-Java library and tests
• target -- The compiled library file, cql-java.jar and javadoc
• bin -- Simple shell-scripts to invoke CQL programs (parser/lexer/generator)
• util -- Various testing and sanity-checking Perl scripts
• etc -- Other files: PQF indexes, generator properties, etc.

Compilation and Installation

The build process is controlled by Maven so compilation is the standard:

mvn clean install

which generates build artifacts under target/.

"Installation" of this package would consist of putting the bin directory on your PATH and target/cql-java.jar on your CLASSPATH.

Synopsis

Using the test-harnesses:

$ CQLParser 'title=foo and author=(bar or baz)'
$ CQLParser -c 'title=foo and author=(bar or baz)'
$ CQLParser -p /etc/pqf.properties 'dc.title=foo and dc.author=bar'
$ CQLLexer 'title=foo and author=(bar or baz)'
	(not very interesting unless you're debugging)
$ CQLGenerator etc/generate.properties seed 18

Using the library in your own applications:

import org.z3950.zing.cql.*

// Building a parse-tree by hand
CQLNode n1 = new CQLTermNode("dc.author", new CQLRelation("="),
			     "kernighan");
CQLNode n2 = new CQLTermNode("dc.title", new CQLRelation("all"),
			     "elements style");
CQLNode root = new CQLAndNode(n1, n2);
System.out.println(root.toXCQL(0));

// Parsing a CQL query
CQLParser parser = new CQLParser();
CQLNode root = parser.parse("title=dinosaur");
System.out.print(root.toXCQL(0));
System.out.println(root.toCQL());
System.out.println(root.toPQF(config));
// ... where `config' specifies CQL-qualfier => Z-attr mapping

Description

See the automatically generated class documentation in the "target" subdirectory.

Author

Original code and documentation by Mike Taylor, Index Data mike@indexdata.com At present maintained by Jakub Skoczen, Index Data jakub@indexdata.dk

• http://www.indexdata.com/cql-java

Please email us with bug-reports, wishlist items, patches, deployment stories and, of course, large cash donations.

Licence

The CQL-Java suite is Free Software, which is pretty much legally equivalent -- though not morally equivalent -- to Open Source. See http://www.gnu.org/philosophy/free-software-for-freedom.html for a detailed if somewhat one-sided discussion of the differences, and particularly of why Free Software is an important idea.

CQL-Java is distributed under version 2.1 of the LGPL (GNU LESSER GENERAL PUBLIC LICENSE). A copy of the licence is included in this distribution, as the file LGPL-2.1. This licence does not allow you to restrict the freedom of others to use derived versions of CQL-Java (i.e. you must share your enhancements), but does let you do pretty much anything else with it. In particular, you may deploy CQL-Java as a part of a non-free larger work.

See also

• http://zing.z3950.org/cql
• Adam Dickmeiss's CQL compiler, written in C.
• Rob Sanderson's CQL compiler, written in Python.
• Jakub Skoczen's CQL-js compiler, written in JavaScript https://github.com/indexdata/cql-js
• All the other free CQL compilers everyone's going to write :-)
• The Changes file, including the "Still to do" section.