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摘要
En 中文
If today's software developers use models at all, they use them mostly as simple sketches of design ideas, often discarding them once they've written the code. This is sufficient for traditional code-centric development. With a model-driven approach, however, the models themselves become the primary artifacts in the development of software. In this case, a clear, common understanding of the semantics of our modeling languages is at least as. important as a clear, common understanding of the semantics of our programming languages. There has been, and continues to be, a great deal of discussion within the software community on modeling and metamodeling and the relationships between modeling languages and metamodeling languages. Such relationships' circular nature makes them particularly hard to discuss clearly, often hiding many important but subtle issues at the foundation of what we do when we model. To address these issues as clearly as possible, I examine a set of questions whose answers, taken together, will help us understand the fundamental question, What do models mean? The result is a set of careful definitions for key terms that will let us cut through some of this topic's more confusing aspects. To understand the intent behind these definitions, we must also look at how other disciplines use models. After all, we should realize that, with a true model-driven approach to software development, we are using models in much the same way that other scientific and engineering disciplines use them. So, I've illustrated the definitions with simple (nontechnical) discussions of modeling in Newtonian physics and its application to engineering. The article's primary goal is, however, to discuss the modeling of software. Since the Object Management Group first specified the Unified Modeling Language in 1997, UML has become the common modeling language of the software development community. (UML's current version is 1.5;(1) the draft specifications for Version 2.0 are entering the OMG finalization process.(2,3)) Thus, any discussion of software models must employ UML terms, as I do in this article. Nevertheless, we begin first not with an inquiry into the modeling language but with an even more basic question.
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