Backend Data Options for UWL

Gang,

We are looking to implement a completely custom workflow application into the portal... with data for each item stored in a SQL DB.

Can we get to this data and expose it through the UWL interface or are we limited to "SAP Business Object Repository (ABAP BOR), Business Workflow container (Webflow Container), User Management Engine (UME)" as the "How To" guide indicates?

Thanks.

Brandon