AFM241 Study Guide - Midterm Guide: Cardinality, Unique Key
30 May 2018
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Looking at the association between tProduct and tOrder, we can see that a product may appear in many
orders and an order may have many products.
Having the primary key of a specific product does not allow us to functionally determine specific values
of attributes from the orders table such as order date and customer
Similarly, having the primary key of an order doesn’t allow us to functionally determine a specific
product
Remove M:M before its implementation. This can be done by creating an intersection table
Each record in an intersection table provides a “bridge” that lets us relate a pair of
occurrences of the original tables
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Document Summary
Looking at the association between tproduct and torder, we can see that a product may appear in many orders and an order may have many products. Having the primary key of a specific product does not allow us to functionally determine specific values of attributes from the orders table such as order date and customer. Similarly, having the primary key of an order doesn"t allow us to functionally determine a specific product. This can be done by creating an intersection table. Each record in an intersection table provides a bridge that lets us relate a pair of occurrences of the original tables. An intersection table may or may not have one or more attributes of its own. Intersection table must be created for the proper implementation of a database. Cardinality refers to the maximum and minimum number of occurrences that must be included in a relation. When we establish cardinalities, the direction of the association matters.
