- "What is IDEF1X ?" or
- "What does this symbol mean?"
and consequently we go off on a side trip.
This page introduces IDEF1X and identifies the notation, so that standard-compliant Data Models can be read and fully understood.
There are many closely related subjects, which require formal education and the links are provided below in the list.
- the Relational Model
- 2nd and 3rd Normal Forms in general, and the specific Relational Normalization identified in the Relational Model.
- The IDEF1X Methodology or Relational Database Design
Figure 7-3 shows the different types of relationships using two ER notations:
- the original Chen notation and the
- Crow's Foot notation.
The left side of the ER diagram shows the Chen notation, based on Peter Chen's landmark paper.
In this notation, the connectivities are written next to each entity box. Relationships are represented by a diamond connected to the related entities through a relationship line. The relationship name is written inside the diamond.
The right side of Figure 7-3 illustrates the Crow's Foot notation. The name "Crow's Foot" is derived from the three-pronged symbol used to represent the “many” side of the relationship. As you examine the basic Crow's Foot ERD in Figure 7-3, note that the connectivities are represented by symbols.
For example, the "1" is represented by a short line segment, and the "M" is represented by the three-pronged "crow's foot."
In this example, the relationship name is written above the relationship line.
In Figure 7-3, entities and relationships are shown in a horizontal format, but they may also be oriented vertically.
The entity location and the order in which the entities are presented are immaterial; just remember to read a 1:M
relationship from the "1" side to the "M" side.
The Crow's Foot notation is used as the design standard in this book. However, the Chen notation is used to illustrate some of the ER modeling concepts whenever necessary. Most data modeling tools let you select the Crow’s Foot notation.