Repository

This article is part of the XQuery Portal. It describes how external XQuery modules and Java code can be installed in the XQuery module repository, and how new packages are built and deployed.

=Introduction=

One of the things that makes languages successful is the availability of external libraries. As XQuery comes with only 150 pre-defined functions, which cannot meet all requirements, additional library modules exist – such as FunctX – which extend the language with new features.

BaseX offers the following mechanisms to make external modules accessible to the XQuery processor:


 * 1) The internal Packaging mechanism will install single XQuery and JAR modules in the repository.
 * 2) The EXPath Packaging system provides a generic mechanism for adding XQuery modules to query processors. A package is defined as a .xar archive, which encapsulates one or more extension libraries.

Accessing Modules
Library modules can be imported with the import module statement, followed by a freely choosable prefix and the namespace of the target module. The specified location may be absolute or relative; in the latter case, it is resolved against the location (i.e., static base URI) of the calling module. Import module statements must be placed at the beginning of a module:

Main Module :

 import module namespace m = 'http://basex.org/modules/hello' at 'hello-world.xqm'; m:hello("Universe")

Library Module  (in the same directory):

 module namespace m = 'http://basex.org/modules/Hello'; declare function m:hello($world) { 'Hello ' || $world };

If no location is supplied, modules will be looked up in the repository. Repository modules are stored in the repo directory, which resides in your home directory. XQuery modules can be manually copied to the repository directory or installed and deleted via commands.

The following example calls a function from the FunctX module in the repository:

 import module namespace functx = 'http://www.functx.com'; functx:capitalize-first('test')

=Commands=

There are various ways to organize your packages:


 * Execute BaseX REPO commands (listed below)
 * Call XQuery functions of the Repository Module
 * Use the GUI (Options → Packages)

You can even manually add and remove packages in the repository directory; all changes will automatically be detected by BaseX.

Installation
A module or package can be installed with. The path to the file has to be given as a parameter:

REPO INSTALL http://files.basex.org/modules/expath/functx-1.0.xar REPO INSTALL hello-world.xqm

The installation will only succeed if the specified file conforms to the constraints described below. If you know that your input is valid, you may as well copy the files directly to the repository directory, or edit its contents in the repository without deleting and reinstalling them.

Listing
All currently installed packages can be listed with. The names of all packages are listed, along with their version, their package type, and the repository path:

Name                  Version  Type      Path - http://www.functx.com 1.0      EXPath    http-www.functx.com-1.0

Removal
A package can be deleted with and an additional argument, containing its name or the name suffixed with a hyphen and the package version:

REPO DELETE http://www.functx.com REPO DELETE http://www.functx.com-1.0

=Packaging=

XQuery
If an XQuery file is specified as input for the install command, it will be parsed as XQuery library module. If the file can successfully be parsed, the module URI will be rewritten to a file path and attached with the .xqm file suffix, and the original file will possibly be renamed and copied to that path into the repository.

Example:

Installation (the original file will be copied to the org/basex/modules/Hello sub-directory of the repository):

REPO INSTALL http://files.basex.org/modules/org/basex/modules/Hello/HelloWorld.xqm

Importing the repository module:

 import module namespace m = 'http://basex.org/modules/Hello'; m:hello("Universe")

Java
For general notes on importing Java classes, please read the Java Bindings article on Module Imports.

Java archives (JARs) may contain one or more class files. One of them will be chosen as main class, which must be specified in a Main-Class entry in the manifest file (META-INF/MANIFEST.MF). This fully qualified Java class name will be rewritten to a file path by replacing the dots with slashes and attaching the .jar file suffix, and the original file will be renamed and copied to that path into the repository.

If the class will be imported in the prolog of the XQuery module, an instance of it will be created, and its public functions can then be addressed from XQuery. A class may extend the QueryModule class to get access to the current query context and to be enriched by some helpful annotations (see Annotations).

Example:

Structure of the  archive:

META-INF/ MANIFEST.MF org/basex/modules/ Hello.class

Contents of the file MANIFEST.mf (the whitespaces are obligatory):

Manifest-Version: 1.0 Main-Class: org.basex.modules.Hello

Contents of the file Hello.java (comments removed):

 package org.basex.modules; public class Hello { public String hello(final String world) { return "Hello " + world; } }

Installation (the file will be copied to org/basex/modules/Hello.jar):

REPO INSTALL HelloWorld.jar

XQuery file  (same as above):

 import module namespace m = 'http://basex.org/modules/Hello'; m:hello("Universe")

After having installed the module, all of the following URIs can be used in XQuery to import this module or call its functions (see URI Rewriting for more information):

http://basex.org/modules/Hello org/basex/modules/Hello org.basex.modules.Hello

Additional Libraries
A Java class may depend on additional libraries. The dependencies can be resolved by creating a fat JAR file, i.e., extracting all files of the library archives and producing a single, flat JAR package.

Another solution is to copy the libraries into a lib directory of the JAR package. If the package will be installed, the additional library archives will be extracted and copied to a hidden sub-directory in the repository. If the package will be deleted, the hidden sub-directory will be removed as well.


 * Examplary contents of Image.jar

lib/ Images.jar META-INF/ MANIFEST.MF org/basex/modules/ Image.class


 * Directory structure of the repository directory after installing the package

org/basex/modules/ Image.class .Images/ Images.jar

Combined
It makes sense to combine the advantages of XQuery and Java packages:


 * Instead of directly calling Java code, a wrapper module can be provided. This module contains functions that invoke the Java functions.
 * These functions can be strictly typed. This reduces the danger of erroneous or unexpected conversions between XQuery and Java code.
 * In addition, the entry functions can have properly maintained XQuery comments.

XQuery and Java can be combined as follows:


 * First, a JAR package is created (as described above).
 * A new XQuery wrapper module is created, which is named identically to the Java main class.
 * The URL of the import module statement in the wrapper module must start with the java: prefix.
 * The finalized XQuery module must be copied into the JAR file, and placed in the same directory as the Java main class.

If the resulting JAR file is installed, the embedded XQuery module will be extracted, and will be called first if the module will be imported.


 * Main Module hello-universe.xq:

 import module namespace m = 'http://basex.org/modules/Hello'; m:hello("Universe")


 * Wrapper Module Hello.xqm:

 module namespace hello = 'http://basex.org/modules/Hello';

(: Import JAR file :) import module namespace java = 'java:org.basex.modules.Hello';

(:~ : Say hello to someone. : @param $world  the one to be greeted : @return welcome string :) declare function hello:hello( $world  as xs:string ) as xs:string { java:hello($world) };


 * Java class Hello.java:

 package org.basex.modules;

public class Hello { public String hello(final String world) { return "Hello " + world; } }

If the JAR file is installed, Combined will be displayed as type:

REPO INSTALL http://files.basex.org/modules/org/basex/modules/Hello.jar REPO LIST Name                    Version  Type      Path --- org.basex.modules.Hello -        Combined  org/basex/modules/Hello.xqm

=EXPath Packaging=

The EXPath specification defines how the structure of a .xar archive shall look like. The package contains at its root a package descriptor named. This descriptor presents some meta data about the package as well as the libraries which it contains and their dependencies on other libraries or processors.

XQuery
Apart from the package descriptor, a .xar archive contains a directory which includes the actual XQuery modules. For example, the FunctX XAR archive is packaged as follows:

expath-pkg.xml functx/ functx.xql functx.xsl

Java
If you want to package an EXPath archive with Java code, some additional requirements have to be fulfilled:


 * Apart from the package descriptor, the package has to contain a descriptor file at its root, defining the included jars and the binary names of their public classes. It must be named   and must conform to the following structure:

  ...    ....    ...     ...     ....


 * The jar file itself along with an XQuery file defining wrapper functions around the java methods has to reside in the module directory. The following example illustrates how java methods are wrapped with XQuery functions:

Example: Suppose we have a simple class  having just one public method  :

 package test;

public final class Printer { public String print(final String s) { return new Writer(s).write; } }

We want to extend BaseX with this class and use its method. In order to make this possible we have to define an XQuery function which wraps the  method of our class. This can be done in the following way:

 import module namespace j="http://basex.org/lib/testJar";

declare namespace p="java:test.Printer";

declare function j:print($str as xs:string) as xs:string { let $printer := p:new return p:print($printer, $str) };

As it can be seen, the class Printer is declared with its binary name as a namespace prefixed with "java" and the XQuery function is implemented using the Java Bindings offered by BaseX.

On our file server, you can find some example libraries packaged as XML archives (xar files). You can use them to try our packaging API or just as a reference for creating your own packages.

=Performance=

Importing XQuery modules that are located in the repository is just as fast as importing any other modules. Modules that are imported several times in a project will only be compiled once.

Imported Java archives will be dynamically added to the classpath and unregistered after query execution. This requires some constant overhead and may lead to unexpected effects in scenarios with highly concurrent read operations. If you want to get optimal performance, it is recommendable to move your JAR files into the lib/custom directory of BaseX. This way, the archive will be added to the classpath if BaseX is started. If you have installed a Combined Package, you can simply keep your XQuery module in the repository, and the Java classes will be automatically detected.

=Changelog=


 * Version 9.0


 * Added: Combined XQuery and Java packages
 * Added: Additional Libraries


 * Version 7.2.1


 * Updated: Installation: existing packages will be replaced without raising an error
 * Updated: Removal: remove specific version of a package


 * Version 7.1


 * Added: Repository Module


 * Version 7.0


 * Added: EXPath Packaging