A new RDBMS connector for Ontopia, based on JDO
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Ontopia JDO

This project aims to replace the current Ontopia RDBMS implementation by using the JDO specification.


The main entry classes are located in the net.ontopia.topicmaps.impl.jdo.entry package and operate like other sources. A source can be instantiated programatically or by using a sources xml file.

Via tm-sources.xml

You can add a JDO topicmap source by defining it in a sources xml file like:

<source class="net.ontopia.topicmaps.impl.jdo.entry.JDOTopicMapSource">
  <param name="id" value="jdo"/>
  <param name="title" value="JDO"/>
  <param name="supportsCreate" value="true"/>
  <param name="supportsDelete" value="true"/>
  <param name="propertyFile" value="${CWD}/db.properties"/>

Supported properties of the source are:

  • id: The unique identification of the source
  • title: The human friendly title of the source
  • propertyFile: A reference to a property file containing configuration for JDO / datanucleus. The JDOTopicMapSource uses StreamUtils.getInputStream() to locate the file.
  • supportsCreate: Is creation of new topicmaps allowed?
  • supportsDelete: Is deletion of topicmaps allowed?


A JDOTopicMapSource may be instantiated programatically. The supported fields are equals to those used in the sources xml.

JDOTopicMapSource source = new JDOTopicMapSource();
source.setTitle("JDO source");
// do something with source

Make sure to close the source when it is no longer needed to release all connections to the database.

JDO configuration

This project uses Datanucleus as the JDO implementation of choice. In theory other JDO frameworks can be used, but only Datanucleus was tested in this project.

To configure datanucleus, a set of properties has to be profived by means of a property file:


The first four here are just like when using Ontopia RDBMS. The last property indicates that JDO is allowed to create any meta object in the database that it requires (tables, indices, etc).


The goal of this project is to replace the Ontopia RDBMS connector to achieve:

  • Less and newer code: the RDBMS packages are big, and most of the code is very old
  • More database support: we no longer program/configure the supported databases, but benefit from the huge list of supported databases directly.
  • External optimization: optimization is (mostly) part of the JDO abstraction layer, which means we won't have to program it
  • Use of open source community: JDO and Datanucleus are maintained by a large open source community, which means we get improvements on each new version
  • Better integration: extending Ontopia's datamodel with your own JDO persisted Pojos should now be possible.


This project is the first beta version. It has been tested within the scope of Ontopia code, and has been tested by Morpheus by integration into existing projects. So far, only H2 and Postgresql have been tested as backends.

We aim to have Ontopia JDO be part of the release candidates for Ontopia 6.0. A requirement of this is that more testing has to be done, in many more backends.