When Selecting an Identifier, One Should

Multiple Choice

When selecting an identifier, one should:

A) use intelligent keys.
B) use large composite keys instead of single-attribute surrogate keys.
C) choose a candidate key that will not change its value over the life of each instance of the entity type.
D) choose a candidate key such that for each instance of the entity, the attribute is guaranteed to have valid values or is null.
E) choose a candidate key that allows for duplicate values.