A crow's foot is used to describe the "many" side of a one-to-many or many-to-many relationship, as
highlighted in Figure 7-5. A crow's foot looks quite literally like the imprint of a crow's foot in the earth, with three splayed "toes."
By now, you should get the idea that many toes implies more than one and thus many, regardless of how many toes a crow
actually has. Figure 7-5 shows a crow's foot between the AUTHOR and PUBLICATION tables, indicating a
one-to-many relationship between AUTHOR and PUBLICATION tables.
Figure 7-5: A crow's foot represents the many sides of a one-to-many relationship.
Ad Relational Database Design
Four Relationships described with Crow's Foot Notation
1:1 relationship:
1. Each employee is assigned to an office and an office is assigned to only one employee
1:N relationship:
2. Each Product originates from a single supplier but each supplier can furnish many products
Unresolved M:N relationship:
3. Each class consists of many students and each student can take many classes
Resolved M:N relationship:
4. This is how you illustrate the resolved version of the same M:N relationship