Instantiate meta-model classes for JPA 2.0 from XML descriptors

JPA 2.0 has introduced a specification for strictly-typed dynamic query construction. The type-strictness is based on availability of a meta-model. The user application can either use meta-model API to access the type information or instantiate the meta-model (referred as canonical meta-model) with a set of auto-generated classes for compile-time binding. This issue refers to instantiating the canonical meta-model at compile-time.
The process involves processing source code annotations or xml descriptors.

Annotation processing support in Java platform has significantly changed across JDK version 5 and 6. In JDK5, the annotation processing was supported by a command-line tool named apt based on com.sun.mirror API library. In JDK 6, the annotation processing is more seamlessly integrated with javac compilation process with javax.annotation API libraries.

It is not obvious at this point on how to hook into compiler life-cycle when source code has no annotation and persistence meta-data is only available in XML descriptors.