Data Modeling › Virtual Fields › Sequence of Relations and Virtual Fields

Sequence of Relations and Virtual Fields

With a self-referencing file such as HORSE, the sequence numbers you entered previously against the database relations are significant when specifying virtual fields.

CA 2E uses a single-pass algorithm to resolve entries on a file. When CA 2E looks for virtual fields, it resolves all the relations for the referenced file in the order that they appear on the Edit Database Relations panel. The following figure shows both the default relation order for the HORSE file and the order determined by the sequence numbers you entered earlier in this tutorial.

Because the HORSE file refers to itself, any relations that occur after the Refers to HORSE relations will not have been resolved at the time CA 2E attempts to resolve the virtual fields for the Refers to relations. In other words, if you had not inserted sequence numbers for the HORSE file relations, the Has relations would not have been resolved at the time CA 2E needed to resolve the Refers to relations. As a result,CA 2E could not have created the virtual entries for the Horse name and Date of birth fields.