I was showing examples of both complete and incomplete definitions during a recent training class, when I shared the following incomplete definition for a Customer Id:

A Customer Id is the unique identifier for a Customer.

“What else can you say about Customer Id anyway?” a participant asked.

What else can you say about Customer Id (or any identifier) to add more meaning to its definition?

See the Appendix for my answers.

 

Key Points

·         A key is a data element or set of data elements that helps us find entity instances.

·         A candidate key is a set of one or more data elements that uniquely identify an entity instance.

·         A candidate key becomes either a primary or alternate key.

·         A primary key represents the one or more data elements that uniquely identify an instance of an entity and that is chosen to be the unique identifier everyone should use. In contrast, an alternate key also uniquely identifies entity occurrences, but is not chosen as the unique key.

·         If a key contains more than one data element, it is known as a composite key.

·         A surrogate key is a primary key with no embedded intelligence that is a substitute for a natural key. It is used by IT to facilitate integration and introduce database efficiencies.

·         A foreign key points from one entity instance to another.

·         The PowerDesigner CDM does not support foreign keys.

·         PowerDesigner uses the word ‘identifier’ in the CDM and LDM, and ‘key’ in the PDM.

 

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