7.23

Explain what is meant by repetition of information and inability to represent information. Explain why each of these properties may indicate a bad relational-database design.

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• repetition of information : When inserting data into our database model, if the model requires us to insert the same information multiple times, then we say our database model has the repetition of information issue. Note that we may sometimes intentionally want some information to be repeated for performance reasons.

• inability to represent information : If the database model was not designed well or not taking into account some things in reality, then the issue of “inability to represent information” may arise. For example, in our university schema if we removed the department relation, and instead used the schema instructor(ID, name, dept_name, salary) to represent both the instructor and the departments in the university, then our database model would NOT be able to represent a department having no instructors.