About IDO secondary tables
There are situations where you might want to include read-only information from associated tables in your IDO. Suppose, for instance, that you store a "Unit of Measure" code in your base table. The description associated with this code is stored in a separate Unit of Measure code table. You can publish the Unit of Measure description on your IDO by adding a secondary table to the IDO.
Columns from secondary tables can be published in the IDO as read-only properties. Secondary tables do not need to have the same primary key columns as the base tables, but you must specify the join criteria needed to include columns from secondary tables in your IDO.