Uniqueness constraints such as keys and functional dependencies in the relational model are a core concept in information systems technology. We consider uniqueness constraints suitable for object relational data models and identify a boundary between tractable and intractable varieties. The subclass that is tractable is still a strict generalization of both keys and relational functional dependencies. We present an efficient decision procedure for the logical implication problem of this subclass. The problem itself is formulated as an implication problem for a simple dialect of description logic (DL). DLs are a family of languages for knowledge representation that have many applications in information systems technology and for which model building procedures have been developed that can decide implication problems for dialects that are very expressive. Our own procedure complements this approach and can be integrated with these earlier procedures. Finally, to motivate our results, we review some applications of our procedure in query optimization.