Relationships between two Supertype Entities connecting to the same Subtype Entity should not be allowed, but erwin allows that. How can I prevent an Entity from being a Subtype to more than one Supertype Entity?
With version 2018 R1, erwin Data Modeler (DM) now gives you better control over the creation of a Supertype-Subtype Relationship between two different Supertype Entities and same Subtype Entity. An option to enable/disable such Relationships has been provided on the Model Editor.
If the check box ‘Enforce Relationship Rule’ is enabled (selected), you will not be able to add a second Supertype-Subtype Relationship from another Supertype Entity to an existing Subtype Entity. It will now give you the following error which will pop up when creating a Supertype-Subtype Relationship between the Entities ‘Supertype2’ and ‘Subtype2’:
With erwin DM 2018 R1, it is now enabled by default and a Supertype-Subtype Relationship between two different Subtype Entities belonging to same or different Supertype group is not allowed. However, if you have a model created in an older version of erwin DM with such a Supertype-Subtype Relationship, the Relationship is preserved when you open the model in erwin DM 2018 R1 or later.
However, if you want to keep modeling the older way, you can disable (deselect) the check box in Model Properties and can draw a Supertype-Subtype Relationship as in the screen shot below.
Please note that it is now possible to have both kinds of rules in the same model as checking or un-checking enables and disables for any action taken after the box is checked or unchecked and does not impact the existing Relationships.