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Making Software by Greg Wilson, Andy Oram

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Chapter 21. How Effective Is Modularization?

Neil Thomas

Gail Murphy

For more than 30 years, the concept of modularity has been seen as a key enabler for the development of large software systems. Modules help manage the complexity of development by breaking a system into units of software that individuals or teams can build [Dijkstra 1968], [Parnas 1972]. Modules enable the hiding of decisions behind an interface, allowing the individual or team responsible for a module to make progress independent of the decisions made by individuals and teams responsible for other modules [Parnas 1972]. Modules enable the enforcement of boundaries between parts of the software system, enabling the interchange of one part for another [Dijkstra 1968], minimizing the impact of changes made to a specific part of the system [Parnas 1972] and reducing the time to build the system when changes are made (separate compilation) [Liskov et al. 1977].

To help programmers maximize these benefits and more, most programming languages provide explicit support for expressing modules. For instance, many object-oriented programming languages, such as Java [Gosling et al. 1996], support a fine-grained notion of modularity through the definition and implementation of abstract data types. Support for coarser-grained modularity can sometimes be found in companion technologies. For instance, OSGi, a companion technology to Java, enables classes to be divided into bundles that are then restricted to communicating through ...

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