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| | *[[Software Engineering and Systems Engineering: Similarities and Differences]] | | *[[Software Engineering and Systems Engineering: Similarities and Differences]] |
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| − | ==On the Nature of Software==
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| − | The nature of the software medium has many consequences for systems engineering of software-intensive systems. Fred Brooks has famously observed that four properties of software, taken together, differentiate it from other kinds of engineering artifacts (Brooks 1995):
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| − | #complexity
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| − | #conformity
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| − | #changeability
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| − | #invisibility
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| − | Brooks states:
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| − | <blockquote>Software entities are more complex for their size than perhaps any other human construct because no two parts are alike (at least above the statement level).</blockquote>
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| − | The complexity of software thus arises from the large number of unique, interacting parts in a software system. The parts are unique because they are encapsulated as functions, subroutines, or objects and invoked as needed rather than being replicated. Software parts have several different kinds of interactions, including serial and concurrent invocations, state transitions, data couplings, and interfaces to databases and external systems. Depiction of a software entity often requires several different design representations to portray the numerous static structures, dynamic couplings, and modes of interaction that exist in computer software. A seemingly “small” change in requirements is one of the many ways that complexity of the product may affect management of a project. Complexity within the parts and in the connections among parts may result in a large amount of rework for a “small” change in requirements, thus upsetting the ability to make progress according to plan. For this reason, many experienced software engineers say there are no small requirements changes. Complexity can also hide defects that may not be discovered immediately and thus require additional, unplanned rework later.
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| − | Software must conform to exacting specifications in the representation of each part, in the interfaces to other internal parts, and in the connections to the environment in which it operates. A missing semicolon or other syntactic error can be detected by a compiler but a defect in the program logic, or a timing error may be difficult to detect when encountered in operation. Unlike software, tolerance among the interfaces of physical entities is the foundation of manufacturing and assembly; no two physical parts that are joined together have, or are required to have, exact matches. There are no corresponding tolerances in the interfaces among software entities or between software entities and their environments. Interfaces among software parts must agree exactly in numbers and types of parameters and kind of couplings. There are no interface specifications for software stating that a parameter can be “an integer plus or minus 2%.”
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| − | Lack of conformity can cause problems when an existing software component cannot be reused as planned because it does not conform to the needs of the product under development. Lack of conformity might not be discovered until late in a project, thus necessitating development and integration of an acceptable component to replace the one that cannot be reused. This requires unplanned allocation of resources and can delay product completion. Complexity may have made it difficult to determine that the reuse component lacked the necessary conformity until the components it would interact with were completed.
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| − | Changeability is Brooks’ third factor that makes software development difficult. Software coordinates the operation of physical components and provides most of the functionality in software-intensive systems . Because software is the most easily changed element (i.e., the most malleable) in a software-intensive system, it is the most frequently changed element, particularly in the late stages of a development project or during system sustainment. This does not, however, mean that software is easy to change because of complexity and the need for conformity in software. Changing one part of a software system often results in undesired side effects in other parts of the system that must then be changed.
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| − | The fourth of Brooks’ factors is invisibility. Software is said to be invisible because it has no physical properties. While the effects of executing software on a digital computer are observable, software itself cannot be seen, tasted, smelled, touched, or heard; our five human senses are incapable of directly sensing software; software is thus an intangible entity. Work products such as requirements specifications, design documents, source code, and object code are representations of software but they are not the software. At the most elemental level, software resides in the magnetization and current flow in an enormous number of electronic elements within a digital device. Because software has no physical presence, software engineers use different representations, at different levels of abstraction, in an attempt to visualize the inherently invisible entity.
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| − | In addition to the four essential properties of software (complexity, conformity, changeability, and invisibility), one additional factor distinguishes software from other kinds of engineering artifacts (Fairley 2009):
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| − | <blockquote>software projects are team-oriented, intellect-intensive endeavors.</blockquote>
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| − | Clearly, other kinds of engineers, including systems engineers engage in team-oriented problem solving but, unlike other engineering artifacts, there is no fabrication phase for software. Software is composed from the thoughts of software engineers and flows though their fingers onto a keyboard and into a computer. Software teams are necessary because it would take too much time for one person to develop a modern software system and because it is unlikely that one individual would possess the necessary range of skills. It has been observed that the issues of team-oriented software development is similar to the issues that would be encountered if a team of authors were to write a novel as a collaborative project (Fairley 2009).
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| − | Software and software projects are unique for the following reasons:
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| − | *Software has no physical properties
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| − | *Software is the product of intellect-intensive teamwork
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| − | *Productivity of software developers is more widely variable than productivity in other engineering disciplines
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| − | *Estimation and planning for software projects is characterized by a high degree of uncertainty
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| − | *Risk management for software projects is predominantly process-oriented
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| − | *Software alone is useless; software is always part of a larger system
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| − | *Software is the most frequently changed element of systems that incorporate software
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| | ==An Overview of the SWEBOK Guide== | | ==An Overview of the SWEBOK Guide== |
Revision as of 12:13, 2 September 2011
Software is usually prominent in modern systems architectures and is often the glue for integrating complex system components. Software engineering and systems engineering are not merely related disciplines; they are intimately intertwined; see Intertwined Disciplines and the SEBoK.
The SEBoK explicitly recognizes and embraces the intertwining between SE and SwE, which includes defining the relationship between the SEBoK and the Guide to The Software Engineering Body of Knowledge (SWEBOK), which is published by the IEEE (Abran et al. 2004).
[external link: http://www.swebok.org]
This knowledge area describes the nature of software, provides an overview of the 2004 SWEBOK Guide, describes the concepts that are shared by systems engineers and software engineers, and indicates the similarities and difference in how software engineers and systems engineers apply those concepts and use common terminology in similar and different ways.
Topics
The Systems Engineering and Software Engineering knowledge area contains the following topics:
An Overview of the SWEBOK Guide
The Preface to the 2004 version of the Guide to the Software Engineering Body of Knowledge states external link: http://www.swebok.org]:
The purpose of the Guide to the Software Engineering Body of Knowledge is to provide a consensually validated characterization of the bounds of the software engineering discipline and to provide a topical access to the Body of Knowledge supporting that discipline.
Version 3 of the SWEBOK Guide is being developed and will be completed in late 2011 or early 2012. Version 3 of the SWEBOK Guide contains 15 knowledge areas:
- Software Requirements
- Software Design
- Software Construction
- Software Testing
- Software Engineering Methods
- Software Maintenance
- Software Configuration Management
- Software Quality
- Software Engineering Process
- Software Engineering Management
- Software Professional Practice
- Software Economics
- Computing Foundations
- Mathematical Foundations
- Engineering Foundations
The description of each knowledge area includes an introduction, a descriptive breakdown of topics and sub-topics, recommended references, references for further reading, and a list of standards most relevant to the knowledge area.
The following table indicates the correspondences between SWEBOK knowledge areas and SEBoK knowledge areas. The similarities and differences are described below [{Systems Engineering and Software Engineering: Similarities and Differences}].
Table 1. Correspondences between SWEBOK and SEBoK Knowledge Areas
NOTE: Table 1 To be completed
The SWEBOK Guide also contains a chapter on related disciplines, which include:
- Computer Engineering
- Business Management
- Project Management
- Quality Management
- Systems Engineering
The related disciplines are those that share a boundary, and often a common intersection, with software engineering. The SWEBOK Guide does not characterize the knowledge of the related disciplines but rather indicates how those disciplines interact with the software engineering discipline.
References
Citations
(Brooks 1995) Brooks, Fred. 1995. The Mythical Man-Month, Anniversary Edition. Boston, Massachusetts: Addison Weslley Longman Inc.
(Fairley 2009) Fairley, Richard E. 2009. Managing and Leading Software Projects. Hoboken, New Jersey: John Wiley and Sons.
(SWEBOK 2004) Abran et al. 2004. Guide to the Software Engineering Body of Knowledge (SWEBOK. Piscataway, New Jersey: The Institute of Electrical and Electronic Engineers, Inc.
Primary References
(Brooks 1995) Brooks, Fred. 1995. The Mythical Man-Month, Anniversary Edition. Boston, Massachusetts: Addison Weslley Longman Inc.
(Fairley 2009) Fairley, Richard E. 2009. Managing and Leading Software Projects. Hoboken, New Jersey: John Wiley and Sons.
Additional References
(SWEBOK 2004) Abran et al. 2004. Guide to the Software Engineering Body of Knowledge (SWEBOK). Piscataway, New Jersey: The Institute of Electrical and Electronic Engineers, Inc.
Article Discussion
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Signatures
--Bkcase 19:07, 22 August 2011 (UTC) (on behalf of Dick Fairley)