Question

What’s the difference between the CategorySection-Category relationship and the CategorySection-Categorization relationship?

1. CategorySection-Category has an
   arrowhead and a black dot.
2. CategorySection-Categorization has
   an arrowhead on both ends.

Both are supposed to be “has many” relationships but this diagram uses a different symbol to represent these two relationships.

Answer 1

It depends on tyhe notation you are using but typically:

• the crowsfoot (arrow) indicates many
• the black dot indicates required
• the white dot indicates optional

Note that just because a diagram is drawn doesn’t makes the relationships it shows sensible, or even possible.