ch7 - Ian Sommerville 2000 Software Engineering, 6th...

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Unformatted text preview: Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 1 System models l Abstract descriptions of systems whose requirements are being analysed Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 2 Objectives l To explain why the context of a system should be modelled as part of the RE process l To describe behavioural modelling, data modelling and object modelling l To introduce some of the notations used in the Unified Modeling Language (UML) l To show how CASE workbenches support system modelling Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 3 Topics covered l Context models l Behavioural models l Data models l Object models l CASE workbenches Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 4 System modelling l System modelling helps the analyst to understand the functionality of the system and models are used to communicate with customers l Different models present the system from different perspectives External perspective showing the systems context or environment Behavioural perspective showing the behaviour of the system Structural perspective showing the system or data architecture Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 5 Structured methods l Structured methods incorporate system modelling as an inherent part of the method l Methods define a set of models, a process for deriving these models and rules and guidelines that should apply to the models l CASE tools support system modelling as part of a structured method Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 6 Method weaknesses l They do not model non-functional system requirements l They do not usually include information about whether a method is appropriate for a given problem l The may produce too much documentation l The system models are sometimes too detailed and difficult for users to understand Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 7 Model types l Data processing model showing how the data is processed at different stages l Composition model showing how entities are composed of other entities l Architectural model showing principal sub- systems l Classification model showing how entities have common characteristics l Stimulus/response model showing the systems reaction to events Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 8 Context models l Context models are used to illustrate the boundaries of a system l Social and organisational concerns may affect the decision on where to position system boundaries l Architectural models show the a system and its relationship with other systems Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7 Slide 9 The context of an ATM system Auto-teller system Security system Maintenance system Account database Usage database Branch accounting system Branch counter system Ian Sommerville 2000 Software Engineering, 6th edition. Chapter 7Software Engineering, 6th edition....
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ch7 - Ian Sommerville 2000 Software Engineering, 6th...

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