How to model an “is a” relationship in an ERD using Crow’s foot notation?

Question

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).

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:

http://en.wikipedia.org/wiki/Enhanced_entity%E2%80%93relationship_model

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

https://www.google.com/search?q=enhanced+er+images&rlz=1C1CHFX_enUS586US586&espv=2&biw=1600&bih=775&tbm=isch&imgil=E75HgoIGspploM%253A%253B5D6WMu1kSMfWrM%253Bhttp%25253A%25252F%25252Fwww.siue.edu%25252F~dbock%25252Fcmis450%25252F4-eermodel.htm&source=iu&pf=m&fir=E75HgoIGspploM%253A%252C5D6WMu1kSMfWrM%252C_&usg=__MdUOOzgIiqsPSTBQjFkTyRuaAlQ%3D&dpr=1&ved=0CDEQyjc&ei=TpMBVeDoKMOjgwSerIOYBg#imgdii=_

I generally use the triangle notation.