Sap Business ByDesign integration with PoS system

For SAP ByDesign which we require, there is a need to integrate with a PoS (Point of Sales) system which is developed in .NET. Is full database access sufficient from the PoS database?

Would a full copy of the PoS system be needed for integration?

We intended to read off the PoS database and pull the relevant information into SAP ByDesign. As such do we need

1) just the database from PoS; or

2) we would need to have the PoS database together with the PoS system?

I am a user and would like to find out more.