Fragments of relations
David Maier, Jeffrey David Ullman · 1983
We develop a theory of relations that are constructed by the union and selection operations from fragment relations. Algorithms for inserting and deleting from relations that are composed of physical fragments are discussed, and we show when such insertions and deletions are meaningful. We also show how to find an access set for a relation, that is, a set of fragments sufficient to produce the relation, and we apply the test to the question of how the fragmentation of relations interacts with a query on the relation, showing that a selection on the relation can be implemented by retrieving a set of physical fragments that forms an access set for another particular relation.