An extension of the relational data model to incorporate ordered domains

摘要: We extend the relational data model to incorporate partial orderings into domains, which we call ordered model. Within extended model, define partially algebra (the PORA) by allowing ordering predicate s be used in formulae of selection operator (σ). The PORA expresses exactly set all possible relations that are invariant under order-preserving automorphism databases. This result characterizes expressiveness and justifies development Ordered SQL (OSQL) as a query language for OSQL provides users with capability capturing semantics many advanced applications, such those having temporal or incomplete information. functional dependencies (OFDs) on databases studied, based two extensions domain orderings: pointwise lexicographical ordering. present sound complete axiom system OFDs first case establish chase rules second. Our results suggest implication problems both cases decidable enforcement practically feasible. In wider perspective, proposed explores an important area object-relational databases, since domains can viewed general kind type.