CQL-Java -- a free CQL parser and related tools, for Java
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,
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
"Installation" of this package would consist of putting the bin
directory on your PATH and
target/cql-java.jar on your CLASSPATH.
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
See the automatically generated class documentation in the "target" subdirectory.
Please email us with bug-reports, wishlist items, patches, deployment stories and, of course, large cash donations.
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.
- Adam Dickmeiss's CQL compiler, written in C.
- Rob Sanderson's CQL compiler, written in Python.
- All the other free CQL compilers everyone's going to write :-)
Changesfile, including the "Still to do" section.