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Crow's Foot Notation used in Data Model

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