Software Engineering Chapter 2

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Socio-technical Systems

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 1

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Objectives●

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To explain what a socio-technical system is and the distinction between this and a computer-based system To introduce the concept of emergent system properties such as reliability and security To explain system engineering and system procurement processes To explain why the organisational context of a system affects its design and use To discuss legacy systems and why these are critical to many businesses

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 2

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Topics covered●●●●

Emergent system properties Systems engineering Organizations, people and computer systems Legacy systems

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 3

Software Engineering, 7th edition的英文课件作者Ian Sommerville

What is a system?●

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A purposeful collection of inter-related components working together to achieve some common objective. A system may include software, mechanical, electrical and electronic hardware and be operated by people. System components are dependent on other system components The properties and behaviour of system components are inextricably inter-mingled

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 4

Software Engineering, 7th edition的英文课件作者Ian Sommerville

System categories●

Technical computer-based systems Systems that include hardware and software but where the operators and operational processes are not normally considered to be part of the system. The system is not self-aware. Systems that include technical systems but also operational processes and people who use and interact with the technical system. Socio-technical systems are governed by organisational policies and rules.

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Socio-technical systems

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 5

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Socio-technical system characteristics●

Emergent properties Properties of the system of a whole that depend on the system components and their relationships. They do not always produce the same output when presented with the same input because the systems’s behaviour is partially dependent on human operators. The extent to which the system supports organisational objectives does not just depend on the system itself.

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Non-deterministic

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Complex relationships with organisational objectives

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 6

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Emergent properties●

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Properties of the system as a whole rather than properties that can be derived from the properties of components of a system Emergent properties are a consequence of the relationships between system components They can therefore only be assessed and measured once the components have been integrated into a system

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 7

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Property

Volume

Reliability

SecurityDescriptionThe volume of a system (the total space occupied) varies depending on how thecomponent assemblies are arranged and connected.System reliability depends on component reliability but unexpected interactions cancause new types of failure and therefore affect the reliability of the system.The security of the system (its ability to resist attack) is a complex property that

cannot be easily measured. Attacks may be devised that were not anticipated by the

system designers and so may defeat built-in safeguards.

This property reflects how easy it is to fix a problem with the system once it has been

discovered. It depends on being able to diagnose the problem, access the components

that are faulty and modify or replace these components.

This property reflects how easy it is to use the system. It depends on the technical

system components, its operators and its operating environment.RepairabilityUsability

Software Engineering, 7th edition的英文课件作者Ian Sommerville

Types of emergent property●

Functional properties These appear when all the parts of a system work together to achieve some objective. For example, a bicycle has the functional property of being a transportation device once it has been assembled from its components. Examples are reliability, performance, safety, and security. These relate to the behaviour of the system in its operational environment. They are often critical for computer-based systems as failure to achieve some minimal defined level in these properties may make the system unusable.

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Non-functional emergent properties

©Ian Sommerville 2004

Software Engineering, 7th edition. Chapter 2

Slide 9

Software Engineering, 7th edition的英文课件作者Ian Sommerville

System reliability engineering●

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Because of component inter-dependencies, faults can be propagated through the system. System failures often occur because of unforeseen inter-relationships between components. It is probably impossible to anticipate all possible component relationships. Software reliability measures may give a false picture …… 此处隐藏：5288字，全部文档内容请下载后查看。喜欢就下载吧 ……