ISYS3257 Lecture Notes - Data Element, Purchase Order, Relate

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This is a design process that notes the major entities (resources and actions) required by an application and the relationships between them. The goal is to maintain each piece of information exactly once, and link to it whenever it is needed (instead of redundantly copying and maintaining it wherever it is needed). If a logical change would need to be recorded in more than one place, then we have likely erred in our design. For example, a purchase order and customer record must have a common element (customer id?) so that they can be linked. Cardinality is an attribute of the relationship that notes how many of one entity can be linked to how many of the other. many-to-many relationships cause major problems with relational logic and should be corrected by generating another table with one-to-many relationships with each of the original entities.

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