Hi,
Define the link in the schema, on either side (not both) of the relationship. I usually define joins out of the dependent tables. Save, log out and back in. From here you'll be able to traverse the table link in the query modal, generating an 'exists' condition in sql. You can also change the filtering dimension on the first screen of the modal if it's clearer.
Thanks,
-Jon
NB For more advanced use, i.e. FDA, you would query the contracts side directly, then change dimension to the recipient side. In this way you'd be specifying which db you want to execute each query, controlling the amount of data transferred between multiple db's.