Object-class Cardinality Constraints

Object-Class Cardinality Constraints

Introduction

An object-class cardinality constraint restricts the number of objects in an object class.

We write object-class cardinality constraints in the same format as participation constraints and place them inside the top right-hand corner of the object-class rectangle. Shorthand notation may also be used so that if the minimum and maximum values are identical, only a single number or variable need be shown. When an object-class cardinality constraint is not specified, we assume the constraint to be 0:*.

Figure 1. An object-class cardinality constraint

Figure 1 shows an example of an object-class cardinality constraint. There are exactly 50 states in the USA. Hence, the object-class cardinality constraint for the State in the USA object class is 50.


Here is a short quiz so you can test your understanding of object-class cardinality constraints.


Go to the OSA Tutorial ORM Constraints

Go to Co-occurence Constraints Specialization Constraints


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Last updated 22 Sept 1994.
by Mingkang Xu (xmk@osm7.cs.byu.edu), Lei Cao(caol@bert.cs.byu.edu)