JPOX represents the Meta-Data JDO files specified for classes internally with the class (and subclasses) MetaData. MetaData is extended for the particular cases of classes (ClassMetaData), fields (FieldMetaData), collections (CollectionMetaData), and maps (MapMetaData). Each of these classes contains features specific to that component. When a class is identified to the JPOX system, a JDO MetaData file is searched for for that class, and the internal MetaData representation is loaded. This is cached throughout the lifetime of the application (since, with JDO 1.0 at least, MetaData is static).

Please refer to this diagram highlighting the process of MetaData handling in JPOX