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Unary many to many example
Data Management Applications (C170)
Western Governors University
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c170Preview text
Recursive Relationships
As you just learned, a recursive relationship is one in which a relationship can exist between
occurrences of the same entity set. (Naturally, such a condition is found within a unary
relationship.)
Many-to-many Unary relationship example
Unary relationships are common in manufacturing industries. For example, Figure 4 illustrates that a rotor assembly (C-130) is composed of many parts, but each part is used to create only one rotor assembly. Figure 4 indicates that a rotor assembly is composed of four 2-cm washers, two cotter pins, one 2-cm steel shank, four 10-cm rotor blades, and two 2-cm hex nuts. The relationship implemented in Figure 4 thus enables you to track each part within each rotor assembly.
If a part can be used to assemble several different kinds of other parts and is itself composed of many parts, two tables are required to implement the "PART contains PART" relationship. Figure 4. illustrates such an environment. Parts tracking is increasingly important as managers become more aware of the legal ramifications of producing more complex output. In many industries, especially those involving aviation, full parts tracking is required by law.
Another example
At Legacy Research Institute, a physician is assigned as a mentor to zero to many other physicians. Each physician is mentored by one to many other physicians.
and a many-to-one (or zero instead of one). The binary relationship in the first question below is an example of this:
In the figure below, what is the relationship from entity A to entity D?
A. One-to-one
B. One-to-many
C. Many-to-one
D. Many-to-many
In the many-to-many unary you see the same thing:
The one-to-one unary has becomes a one-to-many and many-to-one.
Unary many to many example
Course: Data Management Applications (C170)
University: Western Governors University
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