A. ________ is a description of the database structure. Data independence makes each level immune to changes to lower levels.

__________ refers to the Immunity of the external schemes to changes in the conceptual schema. ___________refers to the Immunity of the conceptual schema to changes in the internal schema. Complete the spaces above using one of the keywords:

Relation, Physical data independence, Logical data independence, Integrity constraint, Validity constraint, Database schema.