Abstract
Horizontal decomposition is the process of splitting a relation into sub-relations, called fragments, each containing a subset of the rows of the original relation. In this paper, we consider horizontal decomposition in a setting where some of the attributes in the database schema are interpreted over a specific domain, on which a set of special predicates and functions is defined.
We study the losslessness of horizontal decomposition, that is, whether the original relation can be reconstructed from the fragments by union, in the presence of integrity constraints on the database schema. We introduce the new class of conditional domain constraints (CDCs), restricting the values the interpreted attributes may take whenever a certain condition holds on the non-interpreted ones, and investigate lossless horizontal decomposition under CDCs in isolation, as well as in combination with functional and unary inclusion dependencies.