When I hover over the Title the note identifies the Expense Table as the source table but there is no obvious field identified.
Do you mean that you are hovering over the arrow in the upper left corner of the box named "Expense Table" in Manage | Database | Relationships?
There would be no one field to identify with that information. Each "box" in that window is called a "table occurrence" and when you hover the mouse over the corner arrow, you see the name of the actual table (Defined on the Tables tab) to which that table occurrence refers.
See This tutorial for more on table occurrences: Tutorial: What are Table Occurrences?
Thank you for the refrence to the tutorial. Makes what seemed a bit mystical pretty clear. Kind of a forest through the trees moment. Now to just understand Indexing. Thanks Phil