ERD - Crow's Foot Notation

Question

I am looking at crow's foot notation for db modelling. I have a question around it. I came across a diagram (which I think is crow's foot notation) where I saw that there were 2 entities that had 2 relationship arrows between them. In addition to this, only one end is having minimum and maximum cardinality defined. Other end is just having a single cardinality defined (either 0 or 1).

Does this sound like 'crow's foot notation'? Is this correct? Are there any good tutorials online for learning crow's foot notation?

Answer 1

The great thing about standards is that there are so many to choose from!

There is no such (single) thing as "crows foot notation". As this Wikipedia article explains, there are a number of different tools that use variations on crows foot notation.

Crows foot notation generally involves boxes for entities and lines for relationships. There are typically markings on the relationship lines that illustrate the cardinality at each end of the relationship. The graphical conventions used for marking cardinality vary from one implementation to another. Some people use a graphical convention (square or diagonal crows feet, single or double slashes, arrows, open and filled circles, etc) while others use numbers and letters, like: 0,1 or 1,n etc.

Keep in mind too that different versions of crows foot notation can include other information about the entities and relationships, such as which entities are "strong" and which are "weak" ("weak": part of their candidate key is defined by one or more relationships).

I have always found crows foot notation (I like James Martin's IE notation myself) to be a powerful way of representing an ERD. I think if you pick a convention that you are comfortable with you will be able to get just about any developer or DBA and even most users to understand what you are trying to convey about your data model.

Once you've picked a convention, I'm sure Wikipedia or Google will quickly turn up a reference that will help you learn it easily.