derived extent

A derived extent is a database extent, which is a subset of another extent. Derived extents for the same base extent may define specific set relations as union or distinct, which defines the set relation between the base extent and its derived extents.

A derived extent might be based on more than one base extent, in which case the set relation to its base extents might be intersect, i.e. the derived extent is exactly the intersection of its base extents.