We present a new framework for model management based on system concepts and theory. Underlying the framework is a set of meta-modeling concepts that are useful in capturing the semantics of the modeling process in a modeling environment. These concepts include the notions of a general-model type, type specialization, atomic and composite model versions, model instances, and parameterized versions. We describe these concepts both conceptually and formally and then briefly present a Model Description Language (MDL) that embodies them. While other researchers have suggested some of these concepts primarily in different contexts, this paper makes at least four valuable contributions: (1) the identification of fundamental issues and principles related to model management; (2) the development and enhanced treatment of meta-modeling concepts specifically for model management; (3) the synthesis of those concepts into a coherent, unifying framework for model management; and (4) a demonstration of the practicality of those concepts through a prototype system implementation. Our framework proposes a graph-oriented, nonprocedural, and hierarchical approach for model composition. The framework also supports both model-solver independence and model-data independence. Moreover, it offers general solutions to two critical issues in model management: model-model linkage and model-data linkage. We argue that the system framework can serve as a guide for an effective design of a flexible and extensible model management system. An architecture of such a system and its prototype implementation---called SYMMS---are briefly described. Examples are presented to illustrate the features and advantages of our approach.model management systems, decision support systems, modeling environments, hierarchical model design, systems concepts

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Taking Ein-Dor's recent reevaluation of Grosch's law one step further, the authors find evidence of different slopes for different classes of computers and the utility of an additional variable: the IBM or IBM-compatible factor. The analysis indicates that Grosch's law no longer applies to minicomputers. COMMENTS ON "GROSCH'S LAW RE REVISITED: CPU POWER AND THE COST OF COMPUTATION" YOUNG MOO KANG, ROBERT B. MILLER, and ROGER ALAN PICKAs hardware costs continue to decline and more attention is paid to the economics of software development and operation, hardware nonetheless remains a significant expense. In the face of decisions to be made about centralization versus decentralization of CPU resources, knowledge about economies of scale can help organizations narrow down the choice of alternatives to be seriously considered. For this reason, Ein-Dor's recent reevaluation of the applicability of Crosch's law [1] sparked our interest. Having looked into his analysis, we believe there is yet more information contained in the data Ein-Dor uses than his analysis reveals. Specifically, we find evidence of different slopes for different classes of computers, and the utility of an additional variable-the IBM or IBM-compatible factor. We hope the interest generated by the original article [2, 5] will maintain itself for this further analysis of the same data.

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