Interpreting an ERD

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.

Answer 2

Crowfeet on both ends indicate a many-to-many relationship.

Answer 3

• One Category can have many CategorySections, but one CategorySection can belong to one Category.
• One Categorization can have many Categories, but one Category can belong to only one Categorization.
• A Categorization can have many CategorySections and a CategorySection can belong to many Categorizations.

I think it tells someting like you can create many different categorizations that define different categories but categorysections can be shared among the different categories (and categorizations).