Import Source File Opening problem.

I am using FM 12 adv on windows and mac

As part of my import script, I need to determine if the Source File has particular Tables and/or Fields.

Also, as part of my import script the user 'browses' to whatever prior version of my application they need to import.  Therefore, until the import script is executed, I do not know the path or filename.

Also, as part of my import script I have determined the full file path and filename ($$Path) and have picked off the FM File Name:  ($$Filename).  This works.

So, I've been trying to get up to speed with Execute SQL and I think the Filemaker_Tables and Filemaker_Fields are what I need to make that determination.

The problem:

I need to OPEN $$Filename prior to using the Execute SQL command to make the determination. 

It looks like OPEN FILE does not allow me to specify $$Filename but 'assumes' that the file is all ready present.

Surely this problem has been addressed by more advanced developers?

Thank you

Ron