Software design

This article is about the activity between requirements and programming. For the broader meaning, see software development.
Software development process
Core activities
Paradigms and models
Methodologies and frameworks
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Software design is the process by which an agent creates a specification of a software artifact, intended to accomplish goals, using a set of primitive components and subject to constraints.[1] Software design may refer to either "all the activities involved in conceptualizing, framing, implementing, commissioning, and ultimately modifying complex systems" or "the activity following requirements specification and before programming, as ... [in] a stylized software engineering process."[2]

Software design usually involves problem solving and planning a software solution. This includes both low-level component and algorithm design and high-level, architecture design.

Overview

Software design is the process of implementing software solutions to one or more set of problems. One of the important parts of software design is the software requirements analysis (SRA). It is a part of the software development process that lists specifications used in software engineering. If the software is "semi-automated" or user centered, software design may involve user experience design yielding a storyboard to help determine those specifications. If the software is completely automated (meaning no user or user interface), a software design may be as simple as a flow chart or text describing a planned sequence of events. There are also semi-standard methods like Unified Modeling Language and Fundamental modeling concepts. In either case, some documentation of the plan is usually the product of the design. Furthermore, a software design may be platform-independent or platform-specific, depending upon the availability of the technology used for the design.

Software design can be considered as creating a solution to a problem in hand with available capabilities. The main difference between software analysis and design is that the output of a software analysis consist of smaller problems to solve. Also, the analysis should not be very different even if it is designed by different team members or groups. The design focuses on the capabilities, and there can be multiple designs for the same problem depending on the environment that solution will be hosted. They can be operations systems, webpages, mobile or even the new cloud computing paradigm. Sometimes the design depends on the environment that it was developed for, whether it is created from reliable frameworks or implemented with suitable design patterns.

Software design is both a process and a model. The design process is a sequence of steps that enable the designer to describe all aspects of the software to be built. It is important to note, however, that the design process is not simply a cookbook. Creative skill, past experience, a sense of what makes "good" software, and an overall commitment to quality are critical success factors for a competent design. The design model is the equivalent of an architect’s plans for a house. It begins by representing the totality of the thing to be built (e.g., a three-dimensional rendering of the house) and slowly refines the thing to provide guidance for constructing each detail (e.g., the plumbing layout). Similarly, the design model that is created for software provides a variety of different views of the computer software. Basic design principles enable the software engineer to navigate the design process. Davis [DAV95] suggests a set of principles for software design, which have been adapted and extended in the following list:

Design Concepts

The design concepts provide the software designer with a foundation from which more sophisticated methods can be applied. A set of fundamental design concepts has evolved. They are as follows:

  1. Abstraction - Abstraction is the process or result of generalization by reducing the information content of a concept or an observable phenomenon, typically in order to retain only information which is relevant for a particular purpose.
  2. Refinement - It is the process of elaboration. A hierarchy is developed by decomposing a macroscopic statement of function in a step-wise fashion until programming language statements are reached. In each step, one or several instructions of a given program are decomposed into more detailed instructions. Abstraction and Refinement are complementary concepts.
  3. Modularity - Software architecture is divided into components called modules.
  4. Software Architecture - It refers to the overall structure of the software and the ways in which that structure provides conceptual integrity for a system. A good software architecture will yield a good return on investment with respect to the desired outcome of the project, e.g. in terms of performance, quality, schedule and cost.
  5. Control Hierarchy - A program structure that represents the organization of a program component and implies a hierarchy of control.
  6. Structural Partitioning - The program structure can be divided both horizontally and vertically. Horizontal partitions define separate branches of modular hierarchy for each major program function. Vertical partitioning suggests that control and work should be distributed top down in the program structure.
  7. Data Structure - It is a representation of the logical relationship among individual elements of data.
  8. Software Procedure - It focuses on the processing of each modules individually
  9. Information Hiding - Modules should be specified and designed so that information contained within a module is inaccessible to other modules that have no need for such information

In his object model, Grady Booch mentions Abstraction, Encapsulation, Modularisation, and Hierarchy as fundamental design principles.[3] The acronym PHAME (Principles of Hierarchy, Abstraction, Modularisation, and Encapsulation) is sometimes used to refer to these four fundamental principles.[4]

Design considerations

There are many aspects to consider in the design of a piece of software. The importance of each should reflect the goals the software is trying to achieve. Some of these aspects are:

Modelling language

A modelling language is any artificial language that can be used to express information or knowledge or systems in a structure that is defined by a consistent set of rules. The rules are used for interpretation of the meaning of components in the structure. A modeling language can be graphical or textual. Examples of graphical modeling languages for software design are:

Design patterns

A software designer or architect may identify a design problem which has been solved by others before. A template or pattern describing a solution to a common problem is known as a design pattern. The reuse of such patterns can speed up the software development process, having been tested and proven in the past.[7]

Technique

The difficulty of using the term "design" in relation to software is that in some sense, the source code of a program is the design for the program that it produces. To the extent that this is true, "software design" refers to the design of the design. Edsger W. Dijkstra referred to this layering of semantic levels as the "radical novelty" of computer programming,[8] and Donald Knuth used his experience writing TeX to describe the futility of attempting to design a program prior to implementing it:

TEX would have been a complete failure if I had merely specified it and not participated fully in its initial implementation. The process of implementation constantly led me to unanticipated questions and to new insights about how the original specifications could be improved.[9]

Usage

Software design documentation may be reviewed or presented to allow constraints, specifications and even requirements to be adjusted prior to computer programming. Redesign may occur after review of a programmed simulation or prototype. It is possible to design software in the process of programming, without a plan or requirement analysis,[10] but for more complex projects this would not be considered feasible. A separate design prior to programming allows for multidisciplinary designers and Subject Matter Experts (SMEs) to collaborate with highly skilled programmers for software that is both useful and technically sound.

See also

Wikimedia Commons has media related to Software design.

References

  1. ↑ Ralph, P. and Wand, Y. (2009). A proposal for a formal definition of the design concept. In Lyytinen, K., Loucopoulos, P., Mylopoulos, J., and Robinson, W., editors, Design Requirements Workshop (LNBIP 14), pp. 103–136. Springer-Verlag, p. 109 doi:10.1007/978-3-540-92966-6_6.
  2. ↑ Freeman, Peter; David Hart (2004). "A Science of design for software-intensive systems". Communications of the ACM 47 (8): 19–21 [20]. doi:10.1145/1012037.1012054.
  3. ↑ Booch, Grady; et al. (2004). Object-Oriented Analysis and Design with Applications (3rd ed.). MA, USA: Addison Wesley. ISBN 0-201-89551-X. Retrieved 30 January 2015.
  4. ↑ Suryanarayana, Girish (November 2014). Refactoring for Software Design Smells. Morgan Kaufmann. p. 258. ISBN 978-0128013977. Retrieved 31 January 2015.
  5. ↑ Carroll, ed., John (1995). Scenario-Based Design: Envisioning Work and Technology in System Development. New York: John Wiley & Sons. ISBN 0471076597.
  6. ↑ Bell, Michael (2008). "Introduction to Service-Oriented Modeling". Service-Oriented Modeling: Service Analysis, Design, and Architecture. Wiley & Sons. ISBN 978-0-470-14111-3.
  7. ↑ Judith Bishop. "C# 3.0 Design Patterns: Use the Power of C# 3.0 to Solve Real-World Problems". C# Books from O'Reilly Media. Retrieved 2012-05-15. If you want to speed up the development of your .NET applications, you're ready for C# design patterns -- elegant, accepted and proven ways to tackle common programming problems.
  8. ↑ Dijkstra, E. W. (1988). "On the cruelty of really teaching computing science". Retrieved 2014-01-10.
  9. ↑ Knuth, Donald E. (1989). "Notes on the Errors of TeX" (PDF).
  10. ↑ Ralph, P., and Wand, Y. A Proposal for a Formal Definition of the Design Concept. In, Lyytinen, K., Loucopoulos, P., Mylopoulos, J., and Robinson, W., (eds.), Design Requirements Engineering: A Ten-Year Perspective: Springer-Verlag, 2009, pp. 103-136

^Roger S. Pressman. Software engineering: a practitioner’s approach. McGraw-Hill. ISBN 0-07-365578-3. 

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