Software ENGINEERING-Design Doccumentations

The Design Specification addresses different aspects of the design model and is completed as the designer refines his representation of the software. First, the overall scope of the design effort is described. Much of the information presented here is derived from the System Specification and the analysis model (Software Requirements Specification).

Next, the data design is specified. Database structure, any external file structures, internal data structures, and a cross reference that connects data objects to specific files are all defined.

The architectural design indicates how the program architecture has been derived from the analysis model. In addition, structure charts are used to represent the module hierarchy (if applicable).

The design of external and internal program interfaces is represented and a detailed design of the human/machine interface is described. In some cases, a detailed prototype of a GUI may be represented.

Components—separately addressable elements of software such as subroutines, functions, or procedures—are initially described with an English-language processing narrative. The processing narrative explains the procedural function of a component (module). Later, a procedural design tool is used to translate the narrative into a structured description.

The Design Specification contains a requirements cross reference. The purpose of this cross reference (usually represented as a simple matrix) is (1) to establish that all requirements are satisfied by the software design and (2) to indicate which components are critical to the implementation of specific requirements.

The first stage in the development of test documentation is also contained in the design document. Once program structure and interfaces have been established, we can develop guidelines for testing of individual modules and integration of the entire package. In some cases, a detailed specification of test procedures occurs in parallel with design. In such cases, this section may be deleted from the Design Specification.

Design constraints, such as physical memory limitations or the necessity for a specialized external interface, may dictate special requirements for assembling or packaging of software. Special considerations caused by the necessity for program overlay, virtual memory management, high-speed processing, or other factors may cause modification in design derived from information flow or structure. In addition, this section describes the approach that will be used to transfer software to a customer site.

The final section of the Design Specification contains supplementary data. Algorithm descriptions, alternative procedures, tabular data, excerpts from other documents, and other relevant information are presented as a special note or as a separate appendix. It may be advisable to develop a Preliminary Operations/Installation Manual and include it as an appendix to the design document.
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