【正文】 and costing. Assess effects of change on other requirements。 ? Change implementation. Modify requirements document and other documents to reflect change. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 50 Change management 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 51 Key points ? The requirements engineering process includes a feasibility study, requirements elicitation and analysis, requirements specification and requirements management. ? Requirements elicitation and analysis is iterative involving domain understanding, requirements collection, classification, structuring, prioritisation and validation. ? Systems have multiple stakeholders with different requirements. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 52 Key points ? Social and anisation factors influence system requirements. ? Requirements validation is concerned with checks for validity, consistency, pleteness, realism and verifiability. ? Business changes inevitably lead to changing requirements. ? Requirements management includes planning and change management. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 53 System models 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 54 Objectives ? To explain why the context of a system should be modelled as part of the RE process ? To describe behavioural modelling, data modelling and object modelling ? To introduce some of the notations used in the Unified Modeling Language (UML) ? To show how CASE workbenches support system modelling 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 55 Topics covered ? Context models ? Behavioural models ? Data models ? Object models ? CASE workbenches 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 56 System modelling ? System modelling helps the analyst to understand the functionality of the system and models are used to municate with customers. ? Different models present the system from different perspectives ? External perspective showing the system’s context or environment。 ? Behavioural perspective showing the behaviour of the system。 ? Structural perspective showing the system or data architecture. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 57 Model types ? Data processing model showing how the data is processed at different stages. ? Composition model showing how entities are posed of other entities. ? Architectural model showing principal subsystems. ? Classification model showing how entities have mon characteristics. ? Stimulus/response model showing the system’s reaction to events. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 58 Context models ? Context models are used to illustrate the operational context of a system they show what lies outside the system boundaries. ? Social and anisational concerns may affect the decision on where to position system boundaries. ? Architectural models show the system and its relationship with other systems. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 59 The context of an ATM system A ut o t e l l e rs ys t e mS e c u r i t ys ys t e mM a i n t e na nc es ys t e mA c c o untda ta ba s eU s a geda t a b a s eBr a nc ha c c oun t i n gs ys t e mBr a nc hc oun t e rs ys t e m169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 60 Process models ? Process models show the overall process and the processes that are supported by the system. ? Data flow models may be used to show the processes and the flow of information from one process to another. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 61 Equipment procurement process 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 62 Behavioural models ? Behavioural models are used to describe the overall behaviour of a system. ? Two types of behavioural model are: ? Data processing models that show how data is processed as it moves through the system。 ? State machine models that show the systems response to events. ? These models show different perspectives so both of them are required to describe the system’s behaviour. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 63 Dataprocessing models ? Data flow diagrams (DFDs) may be used to model the system’s data processing. ? These show the processing steps as data flows through a system. ? DFDs are an intrinsic part of many analysis methods. ? Simple and intuitive notation that customers can understand. ? Show endtoend processing of data. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 64 Order processing DFD 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 65 Data flow diagrams ? DFDs model the system from a functional perspective. ? Tracking and documenting how the data associated with a process is helpful to develop an overall understanding of the system. ? Data flow diagrams may also be used in showing the data exchange between a system and other systems in its environment. 169。Ian Sommerville 2022 Software Engineering, 7th edition. Chapter 7 Slide 66 Insulin pump DFD 169。Ian Sommer