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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.


[edit] Introduction

One of the reasons why languages such as Java or Perl have been so successful is the vast amount of libraries that are available to developers. As XQuery comes with only 150 pre-defined functions, which cannot meet all requirements, there is some need for additional library modules – such as FunctX – that extend the language with new features.

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

  1. The default Packaging mechanism will install single XQuery and Java 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.

[edit] 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 HelloUniverse.xq:

import module namespace m = '' at 'HelloWorld.xqm';

Library Module HelloWorld.xqm (in the same directory):

module namespace m = '';
declare function m:hello($world) {
  'Hello ' || $world

Repository modules are stored in a directory named BaseXRepo or repo, which resides in your home directory. XQuery modules can be manually copied to the repository directory or installed and deleted via commands.

If a module has been placed in the repository (see below), there is no need to specify the location. The following example calls a function from the FunctX module:

import module namespace functx = '';

[edit] Commands

There are various ways to handle your packages:

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

[edit] Installation

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

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.

[edit] Listing

All currently installed packages can be listed with REPO LIST. It will return the names of all packages, their version, and the directory in which they are installed:

URI                    Version  Directory
-------------------------------------------------------  1.0

1 package(s).

[edit] Removal

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

REPO DELETE  ...or...

[edit] Packaging

[edit] XQuery

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


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


Importing the repository module:

import module namespace m = '';

[edit] Java

For general notes in 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, 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 Context-Awareness).


Structure of the HelloWorld.jar archive:


Contents of the file (the whitespaces are obligatory):

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

Contents of the file (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 HelloUniverse.xq (same as above):

import module namespace m = '';

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):

[edit] 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 expath-pkg.xml. 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.

[edit] 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:


[edit] Java

In case you want to extend BaseX with a Java archive, some additional requirements have to be fulfilled:

<package xmlns="">

Suppose we have a simple class Printer having just one public method print():

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 print method of our class. This can be done in the following way:

import module namespace j="";

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.

[edit] URI Rewriting

If a module is looked up in the repository, the namespace URI is rewritten to a local file path:

  1. If the URI is a URL:
    1. colons will be replaced with slashes,
    2. in the URI authority, the order of all substrings separated by dots is reversed, and
    3. dots in the authority and the path are replaced by slashes. If no path exists, a single slash is appended.
  2. Otherwise, if the URI is a URN, colons will be replaced with slashes.
  3. Characters other than letters, dots and slashes will be replaced with dashes.
  4. If the resulting string ends with a slash, the index string is appended.

If the resulting path has no file suffix, it may point to either an XQuery module or a Java archive. The following examples show some rewritings:

[edit] Changelog

Version 8.2
Version 7.2.1
Version 7.1
Version 7.0
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