I have to create an entity-relationship diagram (ERD) for an assignment. I am doing this in a particular drawing tool with the Crow’s Foot notation. There is however one thing I cannot figure out:

  • How would you present an “is a” hierarchy in Crow’s Foot notation?

Currently, I am showing this by means of a one-to-one relationship between the Product superentity type and its subtypes (Books, Papers, etc.).

  • Is this the correct way to go or is it wrong? (I could not find any website talking about it).

1 Answer 1


In ER modeling, IsA relationships go by the name "generalization/specialization". A search on this should give you a few pointers. Diagramming this pattern requires using a notation that was originally called "Enhanced ER modeling", although it's been a long time since this extension was introduced.

Here's the wikipedia article:


and here are some sample diagrams, from googling "Enhanced ER Images"


I generally use the triangle notation.

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