Cardinality Guidance

# Cardinality Guidance - Question 3—gives us Min B Question...

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Participation Cardinality Guidance (minB, maxB) (minA, maxA) Entity A Entity B Minimum Maximum 0 – optional participation 1 – one time only participation 1 – mandatory participation M – as many times as needed • Minimum cardinality: expresses the minimum number of times an instance of an entity must participate in a relationship. • Maximum cardinality: expresses the maximum number of times an instance of an entity may participate in a relationship. These questions will help you determine the participation cardinalities for the relationship between Entity A and Entity B. When answering these questions, remember that an “instance” of an entity is one member of that entity set. If, for example, the entity is Sale, an instance is one sales transaction. If the entity is Customer, one specific customer is an instance of that entity set. Assume that you will have data for at least one year of operations in your database. Question 1—gives us Min A Question 2—gives us Max A

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Unformatted text preview: Question 3—gives us Min B Question 4—gives us Max B Note: An instance in the database doesn’t necessarily mean that the company has that item in inventory—it just means that it is set up in the database 1) Can at least one instance of Entity A exist (in the database) without a related instance of Entity B (in the database)? If Yes, minA = 0 (optional) If No, minA = 1 (mandatory) 2) Can at least one instance of Entity A (in the database) be associated with more than one instance of Entity B (in the database)? If Yes, maxA = M (many) If No, maxA = 1 (one) 3) Can at least one instance of Entity B exist (in the database) without a related instance of Entity A (in the database)? If Yes, minB = 0 (optional) If No, minB = 1 (mandatory) 4) Can at least one instance of Entity B (in the database) be associated with more than one instance of Entity A (in the database)? If Yes, maxB = M (many) If No, maxB = 1 (one) Note:...
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Cardinality Guidance - Question 3—gives us Min B Question...

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