I found the way in at last! The specifics here will only apply to the way my system is setup.
I defined a custom metadata field in the LR catalog as an ID field that ties back to my standalone application. I was having a very hard time trying to figure out how to use the ID in my app to get all the info I wanted from the Lr catalog but I found the way. The AgSearchablePhotoProperty table contains the custom metadata field and the image number that is used by Adobe_Images table - this number, via 3 other fields, ties in a very crooked line to all the other tables.
It is a very circuitous path to get to all the information in all the different tables but it can be done.
It goes without saying, if anyone has any thoughts about doing this themselves, be SURE to use a BACKUP copy of the catalog.
If anyone wants to more about how to access the LR catalog via SQL commands you can email me at email@example.com