A directory/catalogue mailmerge working with your flattened workbook would be possible but, as is evident in the tutorial, adding extra subgroup keys increases the complexity. For two keys (e.g. Object_id and Exhibition_id), the examples in the tutorial would already suffice. For some worked examples, see the attachments to the posts at:
https://www.msofficeforums.com/mail-...html#post23345
https://www.msofficeforums.com/mail-...html#post30327
http://windowssecrets.com/forums/sho...l=1#post928391

Alternatively, you may want to try one of the Many-to-One Mail Merge add-ins, from:
Graham Mayor at http://www.gmayor.com/ManyToOne.htm; or
Doug Robbins at http://bit.ly/1hduSCB

That said, the advantages of the DATABASE field include not having to flatten the workbook structure and automatically generating a table for the output. On its own, a directory/catalogue mailmerge doesn't work with multiple sheets and can't directly produce a single table for each group or subgroup.

__________________
Cheers,
Paul Edstein
[Fmr MS MVP - Word]