Model-driven development: The good, the bad, and the ugly & B. Hailpern P. TarrIn large software development organizations, increased complexity of products, shortened development cycles, and heightened expectations of quality have created major challenges at all the stages of the software life cycle. As this issue of the IBM Systems Journal illustrates, there are exciting improvements in the technologies of model-driven development (MDD) to meet many of these challenges. Even though the prevalent software-development practices in the industry are still immature, tools that embody MDD technologies are finally being incorporated in large-scale commercial software development. Assuming MDD pervades the industry over the next several years, there is reason to hope for significant improvements in software quality and time to value, but it is far from a foregone conclusion that MDD will succeed where previous software-engineering approaches have failed. Ó

In commercial software development organizations, increased complexity of products, shortened development cycles, and higher customer expectations of quality have placed a major responsibility on the areas of software debugging, testing, and verification. As this issue of the IBM Systems Journal illustrates, there are exciting improvements in the underlying technology on all three fronts. However, we observe that due to the informal nature of software development as a whole, the prevalent practices in the industry are still immature, even in areas where improved technology exists. In addition, tools that incorporate the more advanced aspects of this technology are not ready for large-scale commercial use. Hence there is reason to hope for significant improvements in this area over the next several years. Since one of the goals of this special issue of the IBM Systems Journal is to be accessible to the students of software engineering at large, we define relevant terminology and its implications (we include formal no

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Programs that implement computer communications protocols can exhibit extremely complicated behavior, and neither informal reasoning nor testing is reliable enough to establish their correctness: In this paper we discuss the application of modular program verification techniques to protocols. This approach is more reliable than informal reasoning, but has an advantage over formal reasoning based op finite-state models: the complexity of the proof need not grow unmanageably.as the size of the program increases. Certain tools of concurrent program verification that are especially useful for protocols' are presented: history varigbles that record sequences of input and output'values, temporal logic for expressing properties that must hold in a future system state (such as eventual receipt of a message), and module specification and composition rules. The use. of these techniqqe5 is illustrated by verifying two data transfer protocols frow 'the literature: the alternating bit protocol and a protocol proposed by Stenning. ' ' of Computer Science, Stanford University, Stanford, CA 94305. He is now with the IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598. S. S . Owicki is with the