Database Reference
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connection, and that is how the cardinality is described; in the case of a
one-to- or zero-to- relationship, a text label “1” or “Z” is added. Addition-
ally, there is usually a text label on the connection that is a verb that de-
scribes the relationship.
Now, Figure 7.4 shows the same objects using the Crow's Feet notation.
F
IGURE
7.4
The Product Vendors entity and its related entities, in the IE Crow's Feet
notation
In this version, at the child entity connection you see a set of three
lines breaking from the main line. This denotes the cardinality of the rela-
tionship and also happens to look like a caveman drawing of a bird's claw
(hence the name of the standard). In this notation, zero, one, and many
connections are labeled with “0,” “1,” or a crow's foot, respectively. If there
is a zero-or-one-to- type of relationship, there will be a “01” on the line at
the appropriate end of the connection. Often, the zeros and ones look like
circles and lines and less like an actual numeral; this often depends on the
modeling tool being used.
Both the IE and the IDEF1X notation styles can be used for data mod-
eling, and both are descriptive enough for all modeling purposes. Which
one you choose is almost irrelevant; it's more important to choose and
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