CayenneModeler GUI tool is intended to work with object relational mapping projects. While you can edit your XML by hand, it is rarely needed, as the Modeler is a pretty advanced tool included in Cayenne distribution. To obtain CayenneModeler, download Cayenne distribution archive from http://cayenne.apache.org/download.html matching the OS you are using. Of course Java needs to be installed on the machine where you are going to run the Modeler.

OS X distribution contains CayenneModeler.app at the root of the distribution disk image.

Windows distribution contains CayenneModeler.exe file in the bin directory.

Cross-platform distribution (targeting Linux, but as the name implies, compatible with any OS) contains a runnable CayenneModeler.jar in the bin directory. It can be executed either by double-clicking, or if the environment is not configured to execute jars, by running from command-line:

java -jar CayenneModeler.jar

The Modeler can also be started from Maven. While it may look like an exotic way to start a GUI application, it has its benefits - no need to download Cayenne distribution, the version of the Modeler always matches the version of the framework, the plugin can find mapping files in the project automatically. So is an attractive option to some developers. Maven option requires a declaration in the POM:

<build>
    <plugins>
        <plugin>
            <groupId>org.apache.cayenne.plugins</groupId>
            <artifactId>maven-cayenne-modeler-plugin</artifactId>
            <version>X.Y.Z</version>
        </plugin>
    </plugins>
</build>

And then can be run as

mvn cayenne-modeler:run