xfa.sourceSet - Undefined

This question has probably been answered a long time ago. But I'm new to LiveCycle designer.

The form that I've created is able to connect to an Oracle database and populate the PDF form.

However, when I execute this code "xfa.sourceSet.DC_SQL.next();"  it gives me the following error.

"TypeError: xfa.sourceSet.DC_SQL is undefined".

Any ideas on how to resolve this issue?

Thanks for your help.