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Fig. 9.1 illustrates the program architecture one would hope was used when when looking

to update, reengineer, or reuse a legacy software application.

Figure 9.1. Layers of a well-structured legacy software application.

Legacy applications that are not sufficiently componentized, such that their general

organization resembles the three layers, are not good candidates for reengineering and

reuse. More often than not, most software development projects in business are done

under fairly aggressive time constraints, therefore it it not uncommon to find an

interleaving of the layers—business logic in the presentation logic, and data access logic

in the business logic. The most widely accepted technique to reuse legacy application

components is that of Wrappering [32], where a new piece of code provides an interface

to a legacy application component or layer without requiring code changes to it. This

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