What is a derived attribute, and should it be stored in the physical model?

• A. It is an attribute that is stored in the database for performance.
• B. A derived attribute is computed from other attributes and is typically not stored.
• C. Derived attributes are always stored because they are needed for queries.
• D. Derived attributes refer to future values.

Answer: (B)

A derived attribute is a value that is calculated from other attributes rather than stored directly. In the physical model, you typically compute it when you query, rather than persisting it, to avoid redundant data and keep things consistent. For example, age can be derived from birth date, and a full name can be built from first name and last name. Storing derived attributes would duplicate data and require extra maintenance whenever the base attributes change. If performance demands it, you might use a computed column, a view, or a materialized/persisted solution, but these are special cases with trade-offs. So, derived attributes are typically not stored in the physical model.