As described in the MetaData Reference, JPOX accepts standard JDO2 metadata, namely jdo files as well as orm files. As always with XML, the metadata must match the defined DTD/XSD for that file type. This section describes the content of the orm files. The content of jdo files can be found here. All orm files must contain a valid DTD/DOCTYPE specification. You can use PUBLIC or SYSTEM versions of these.

Here are a couple of examples valid for orm files with DTD specification

<!DOCTYPE orm PUBLIC
    "-//Sun Microsystems, Inc.//DTD Java Data Objects Mapping Metadata 2.0//EN"
    "http://java.sun.com/dtd/orm_2_0.dtd">


<!DOCTYPE orm SYSTEM "file:/javax/jdo/orm.dtd">

Here is an example valid for orm files with XSD specification

<?xml version="1.0" encoding="UTF-8" ?>
<orm xmlns="http://java.sun.com/xml/ns/jdo/orm"
     xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
     xsi:schemaLocation="http://java.sun.com/xml/ns/jdo/orm
        http://java.sun.com/xml/ns/jdo/orm_2_0.xsd">
    ...
</orm>

Your MetaData should match either the DTD or the XSD specification.