| The increasing importance of integrated databases in several specialized application areas like engineering design (CAD), interactive graphics, image processing, geographical data management, office automation et cetera, has pointed to the limitations of conventional DBMS and the need for more suitable database architectures. This thesis presents a conceptual-level, semantic data model that captures directly the notions of entities, entity interrelationships (representation, version and instance abstractions), and structural abstraction hierarchies (classification, aggregation, generalization and specialization). The model also provides a set of high-level data model operations that can be used to create and manipulate design objects. As well, the structural integrity constraints of entity identity, entity typing, and referential integrity are directly captured by the data model. More complex semantic integrity constraints (including value domain, derived value, entity composition and interface, and mutual consistency constraints) are also provided as explicit, user-specifiable constraints. The object paradigm provides a natural framework for the integration of structural and behavioural abstractions of the design database, and leads to the design of an integrated database language which combines a data type system that provides abstract data types of entity (design object) and value (structured value), and structured types of tuple, set and sequence (complex objects) with a simple procedural, Pascal-like language. The proposed database language, on the other hand, enables user specification of complex, application-specific operations and semantic integrity and consistency constraints at the database schema level. These operations and constraints can be triggered by an integrity subsystem thus providing a means of checking and enforcing the integrity of the design database. These concepts and features of the design database system are illustrated with examples drawn from the domain of VLSI circuit design. Formal algebraic (axiomatic) and model-based (operational) specifications of a structured type system used in defining the semantic data model and the integrated database language are given. A subsystem that provides the structured values of sets, sequences, tuples and unions is also implemented. Finally, a formal denotational semantics specification of the semantic data model and the integrated database language is given using the VDM specification system. These specifications can be used as the basis for implementing particular subsystems of an actual design DBMS, or in rapid prototyping of an experimental version for design analysis, verification and refinement. (Abstract shortened with permission of author.). |
