The Semantics and Expressive Power of the MLR Data

In this paper, we deene the Multilevel Rela-tional (MLR) data model for multilevel relations with element-level labeling. This model builds upon prior work of numerous authors in this area, and integrates ideas from a number of sources. A new data-based semantics is given to the MLR data model which combines ideas from SeaView, belief-based semantics and LDV model, and has the advantages of both eliminating ambiguity and retaining upward information ow. The resulting model is simple, unambiguous and powerful. It has ve integrity properties and ve operation statements for manipulating multilevel relations. In order to support this integration, we introduce several new concepts as well as redeene several old ones. The expressive power of the MLR model is also discussed in this paper, and is compared with several other models. We also address some issues in converting the MLR model to tuple-level labeling, including both scheme mapping and operation interpretation.