Complete Compared to Incomplete Subtype Structures

In IDEF1X, different symbols are used to specify whether or not the set of subtype entities in a subtype relationship is fully defined. An incomplete subtype indicates that the modeler feels there may be other subtype entities that have not yet been discovered. An incomplete subtype is indicated by a single line at the bottom of the subtype symbol, as shown in the figure below:

A complete subtype indicates that the modeler is certain that all possible subtype entities are included in the subtype structure. For example, a complete subtype could capture information specific to male and female employees, as shown in the figure below. A complete subtype is indicated by two lines at the bottom of the subtype symbol.

When you create a subtype relationship, it is a good rule to also create a validation rule for the discriminator. This helps to ensure that all subtypes have been discovered. For example, a validation rule for �account-type� might include: C=checking account, S=savings account, L=loans. If the business also has legacy data with account types of �O,� the validation rule uncovers the undocumented type and lets you decide if the �O� is a symptom of poor design in the legacy system or a real account type that you forgot.