Version Control and Management in Computer-aided Design Databases

There are essentially two characteristics of design objects which impact upon the iterative and probative nature of the design process. first, they are hierarchically formed assemblies of component objects. Second, they have several alternative representations. This dissertation addresses a broad spectrum of modeling and operational issues related to these two aspects in computer-aided design databases. A formal treatment of data modeling concepts, which are defined in terms of primitive constructs of instances, type, homogeneous sets and functions, and abstractions of generalization and composition, is presented for design applications. A classification of composite object attributes into intrinsic interface and extrinsic internal assembly provides an insight into their behavior and functionality. The design process is studied with respect to these classes of attributes. A design evolves in discrete states through mutation and derivation, which may cause version proliferation in the absence of any control mechanism. concepts of invariant attributes and value acquisition are found to be useful for developing a notion of version equivalence. A wide range of methodologies for version management and solutions for the related problems are discussed. The interdependence between composition and generalization graphs suggests that the effect of these graphs on each other must evaluated for maintaining consistency. A time complexity analysis of algorithms devised for this purpose shows a considerably improved performance when the stored, rather than the dynamically computed, transitive closures of these graphs are used. The trade-off it provides far outweighs the space requirement of the transitive closure relations. Owing to the sheer complexity and size of design databases, efficient organization and access of versioned composite objects become imperative. The proposed scheme and its related algorithms can determine an optimal storage organization based on significant units of clustering and expected frequency of retrieval and update operations. A multi-layer architecture is motivated by the accessibility and stability of versions they contain. the proposed protocols for sharing and transition of versions together with change notification provide a unifying framework for managing design in a cooperative CAD environment.

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