In practice requirements and design are inseparable a

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In practice, requirements and design are inseparable A system architecture may be designed to structure the requirements; The system may inter-operate with other systems that generate design requirements; The use of a specific architecture to satisfy non-functional requirements may be a domain requirement. This may be the consequence of a regulatory requirement. 30/10/2014 Chapter 4 Requirements Engineering 42
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12/12/2018 8 Natural language specification Requirements are written as natural language sentences supplemented by diagrams and tables. Used for writing requirements because it is expressive, intuitive and universal. This means that the requirements can be understood by users and customers. Chapter 4 Requirements Engineering 43 30/10/2014 Guidelines for writing requirements Invent a standard format and use it for all requirements. Use language in a consistent way. Use shall for mandatory requirements, should for desirable requirements. Use text highlighting to identify key parts of the requirement. Avoid the use of computer jargon. Include an explanation (rationale) of why a requirement is necessary. 30/10/2014 Chapter 4 Requirements Engineering 44 Problems with natural language Lack of clarity Precision is difficult without making the document difficult to read. Requirements confusion Functional and non-functional requirements tend to be mixed-up. Requirements amalgamation Several different requirements may be expressed together. 30/10/2014 Chapter 4 Requirements Engineering 45 Form-based specifications Definition of the function or entity. Description of inputs and where they come from. Description of outputs and where they go to. Information about the information needed for the computation and other entities used. Description of the action to be taken. Pre and post conditions (if appropriate). The side effects (if any) of the function. 30/10/2014 Chapter 4 Requirements Engineering 46 A structured specification of a requirement for an insulin pump Chapter 4 Requirements Engineering 47 30/10/2014 Tabular specification Used to supplement natural language. Particularly useful when you have to define a number of possible alternative courses of action. For example, the insulin pump systems bases its computations on the rate of change of blood sugar level and the tabular specification explains how to calculate the insulin requirement for different scenarios. 30/10/2014 Chapter 4 Requirements Engineering 48
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12/12/2018 9 Tabular specification of computation for an insulin pump Chapter 4 Requirements Engineering 49 Condition Action Sugar level falling (r2 < r1) CompDose = 0 Sugar level stable (r2 = r1) CompDose = 0 Sugar level increasing and rate of increase decreasing ((r2 r1) < (r1 r0)) CompDose = 0 Sugar level increasing and rate of increase stable or increasing ((r2 r1) (r1 r0)) CompDose = round ((r2 r1)/4) If rounded result = 0 then CompDose = MinimumDose 30/10/2014 Use cases Use-cases are a kind of scenario that are included in the UML.
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  • Fall '19
  • Requirements analysis, Requirements Engineering,  Functional

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