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This cost distribution holds where the costs of specification, design, implementation and integration are measured separately. Notice that system integration and testing is the most expensive development activity.

The evolution costs for generic software products are particularly hard to estimate. In many cases, there is little formal evolution of a product. Once a version of the product has been released, work starts on the next release and, for marketing reasons, this is likely to be presented as a new (but compatible) product rather than a modified version of a product which the user has already bought. Therefore, the evolution costs are not assessed separately as they are in customised software but are simply the development costs for the next version of the system.

What are software engineering methods?

A software engineering method is a structured approach to software development whose aim is to facilitate the production of high-quality software in a cost-effective way. Methods such as Structured Analysis (DeMarco, 1978) and JSD (Jackson, 1983) were first developed in the 1970s. These methods attempted to identify the basic functional components of a system and function-oriented methods are still widely used. In the 1980s and 1990s, these function-oriented methods were supplemented by object-oriented methods such as those proposed by Booch (Booch, 1994) and Rumbaugh (Rumbaugh, Blaha et al., 1991). These different approaches have now been integrated into a single unified approach built around the Unified Modeling Language (UML) (Fowler and Scott, 1997) (Booch, Rumbaugh et al., 1999; Rumbaugh, Jacobson et al., 1999; Rumbaugh, Jacobson et al., 1999).

All methods are based on the idea of developing models of a system which may be represented graphically and using these models as a system specification or design.

There is no ideal method and different methods have different areas where they are applicable. For example, object-oriented methods are often appropriate for interactive systems but not for systems with stringent real-time requirements.

What is case?

The acronym CASE stands for Computer-Aided Software Engineering. It covers a wide range of different types of program which are used to support software process activities such as requirements analysis, system modelling, debugging and testing.

All methods now come with associated CASE technology such as editors for the notations used in the method, analysis modules which check the system model according to the method rules and report generators to help create system documentation. The CASE tools may also include a code generator which automatically generates source code from the system model and some process guidance which gives advice to the software engineer on what to do next.

This type of CASE tool, aimed at supporting analysis and design, is sometimes called an upper-CASE tool because it supports early phases of the software process. By contrast, CASE tools which are designed to support implementation and testing such as debuggers, program analysis systems, test case generators and program editors are sometimes called lower-CASE tools.

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Source:  OpenStax, Software engineering. OpenStax CNX. Jul 29, 2009 Download for free at http://cnx.org/content/col10790/1.1
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