JDO defines XML MetaData in 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
    "-//The Apache Software Foundation//DTD Java Data Objects Mapping Metadata 3.2//EN"
    "https://db.apache.org/jdo/xmlns/orm\_3\_2.dtd">

or

<!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="https://db.apache.org/jdo/xmlns/orm"
    xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
    xsi:schemaLocation="https://db.apache.org/jdo/xmlns/orm https://db.apache.org/jdo/xmlns/orm\_3\_2.xsd" version="3.2">
    ...
</orm>

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