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The transition of legacy systems to a distributed architecture
Ganti N., Brayman W., Wiley-QED Publishing, Somerset, NJ, 1995. Type: Book (9780471060802)
Date Reviewed: Feb 1 1996

One of the hottest topics in information technology is the definition of, and transition to, distributed information systems. For decades, centralized computer systems, with their master databases and online terminals arranged in star networks, were the norm. That is because centralized systems were the only technology in the 1970s and 1980s with the computer power to handle hundreds of applications supporting thousands of online users. As these centralized systems evolved, however, they became inflexible webs of millions of lines of code tying together hundreds of databases. Many of these legacy systems, built with hand-crafted applications to meet individual requirements, have become so complex that they cannot respond to today’s changing needs for data.

The authors define the problems with existing legacy systems, the promise and pitfalls of open systems architectures, and some approaches to migrating to those new architectures. They point out that legacy systems transition is not just surrounding mainframe applications with graphical user interfaces executing on sophisticated workstations. Nor is it just moving mainframe applications onto PCs in a distributed environment. It requires an evolutionary movement away from applications that are tightly coupled to data definitions and toward applications that are more data independent. It also requires re-engineering the business processes to determine which processes to migrate first and what architecture to migrate to. Furthermore, the migration must be done in stages, and each stage must allow for insertion of new technology as it is developed.

The purpose of this book is to present new approaches for deploying information technology in a distributed environment. It accomplishes this purpose by organizing the subject matter into four sections: strategic issues (chapters 1 through 3), conceptual foundations (chapters 4 through 7), alignment of systems with information needs (chapter 8), and the deployment process (chapters 9 through 12). The length is appropriate for the information presented, although I would have liked to see more examples and less theoretical discussion.

The best features of the book are its organization, readability, and clarity. Using the book as a general reference, I found it useful in helping a major federal agency plan for its migration to an open systems environment. Unfortunately, the book tends to stay focused at the conceptual level when the subject matter would have been better explained with a good case study. Thus, the reader must have an extensive systems development background in order to understand how the concepts apply to real-life problems.

Overall, the book does an exceptional job of trying to explain the problems with re-engineering legacy systems and moving them to distributed architectures. It is the first to cover this subject in some detail for an intended audience of both industry professionals and university students. The references are limited to footnotes covering academic papers, conference proceedings, and textbooks, most of which were published within the last five years. The index is adequate, but many subjects that a systems developer would use to search out topics of interest are missing. The diagrams are consistent in format, but do not follow any published standard. Since there are no exercises, the book is best used as a general reference.

I highly recommend the book for those who are facing the daunting problems associated with migration to open systems architectures.

Reviewer:  R. J. Tufts Review #: CR119347 (9602-0095)
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Information Networks (H.3.4 ... )
 
 
Centralization/ Decentralization (K.6.4 ... )
 
 
Distributed Databases (H.2.4 ... )
 
 
Value of Information (H.1.1 ... )
 
 
Distributed Systems (C.2.4 )
 
 
Types Of Systems (H.4.2 )
 
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