ODE -- OModel refactoring and migration

by Fang Zhen for Apache Software Foundation

This proposal is aimed at refactor the OModel for ODE project. Current OModel is not evolveable. When BPEL evolves, new version of OModel objects fail on backward compatibility and compiler/runtime is not flexible enough to the OModel changes like new extension support. I propose JSON serialization and extension plugin mechanism for them respectively. It will reduces work needed for later migrations.