bonita h2 data base
Direct access to database (both Engine and BDM databases) is usually not recommended. This is because the data model is not guarantee to be stable (for Engine database) and because you might perform concurrent operation performed by a process that can lead to invalid data.
The recommendation is to use REST API that provide access to both Engine and BDM information. If you need to update BDM value this is usually done by defining an operation on a process task.
Maybe you can provide a little bit more information about your use case if you need to have guidance to the appropriate API.