BTT version 5.2 adopts the BTT version 4.3 architecture. It is enhanced to support EJB/Web Service interface and WebSphere® pool management.
BTT version 5.1 supports 3 invocation ways: Local Java™, EJB and WSDL. The first two invocation ways are kept in BTT version 5.2, while WSDL invocation is not supported. The BTT version 5.1 JournalService and TableService are replaced by BTT version 4.3 architecture and invocation ways. The definition and usage are still compatible, but the customer extension may not be compatible.
If you use pool service, you need to update your code manually. For example, your service implement BTTPoolable in version 5.1, then you need to implement WebSphere's PoolableObject interface.
BTT version 5.1 service architecture requires you to define a set of properties files and a Factory class and implementation class. In BTT version 5.2, it only requires your service object to implement Externalizable interface and define it in dsesvrce.xml. The getService series function is still workable at both SAE layer and BP layer.
In common cases, you can invoke version 5.1 Journal and Table service by getService() way. You don't need to change the code. But if you invoke them in a special way or make their own customer extensions, some extra work may be needed.