K2 Database Vs Sql Database

So if I want to build some reports that listing the process instance datafields for all processes(be it active or completed), I think it would be better if I create datatables and save the proecess instance datafields in these tables created. Because then it will be very easy to build reports from these tables.

All process instance information (be it active or completed) is saved in the K2Log database. If it would be easy for you to create reports from customized datatables created, you might as well create the reports directly from the K2Log database. The only difficulty would be to understand the layout of the database. Please contact you local K2Workflow support center to obtain a copy of the K2Log database ERD.

I learn that the structure of k2 database is quite different. It lists data sequentially, using GUID or Identity as the key. It won't be so direct to build reports based on K2 databases for developers, some transformations are needed.

True. For performance reasons, it is not recommended to run any reports directly on the K2 transaction database.

Hope this helps,
Ockert