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[...]... the Scene © 2009 John Wiley and Sons 11 System requirements vs software requirements Software -to- be: software to be developed - part of the Software -to- be machine, component of the system- to- be Environment: all other components of the system- to- be, including people, devices, pre-existing software, etc System requirements: what the system- to- be should meet; requirements formulated in terms of phenomena... statements: system requirements, software requirements System requirement: prescriptive statement refering to requirement environment phenomena (not necessarily shared) – to be enforced by the software -to- be possibly together with other system components – formulated in a vocabulary understandable by all parties TrainMoving → DoorsClosed Software requirement: prescriptive statement refering to requirement...What others said Ross'77 Requirements definition must say – why a new system is needed, based on current or foreseen conditions, – what system features will satisfy this context, – how the system is to be constructed Zave'97 RE is concerned with the real-world goals for, functions of, constraints on software systems; and with their – link to precise specifications of software behavior, behavior... environment “The handbrake shall be released when the driver wants to start.” Software requirements: what the software -to- be should meet requirements on its own; formulated in terms of phenomena shared by the software and the environment “The software output variable handBrakeCtrl shall have the value off when the software input variable motorRegime gets the value up.” www.wileyeurope com/college/van... What is Requirements Engineering? – The problem world & the machine solution – The scope of RE: the WHY, WHAT and WHO dimensions – Types of statements involved: descriptive vs prescriptive – Categories of requirements: functional vs non-functional – The requirements lifecycle: actors, processes, products – Target qualities and defects to avoid – Types of software projects – Requirements in the software. .. dimensions System- as-is System- to- be problems, opportunities, system knowledge WHY a new system? Objectives satisfy requirements, constraints, assumptions assignment www.wileyeurope com/college/van lamsweerde Chap.1: Setting the Scene WHAT services? WHO will be responsible for what ? © 2009 John Wiley and Sons 13 ? The WHY dimension Identify, analyze, refine the system- to- be’s objectives – to address... Sons 21 Relating software reqs to system reqs: the 4-variable model [Parnas95] Input Devices (e.g sensors) trainSpeed M: monitored variables Environment DoorsClosed C: controlled variables measuredSpeed I: input data SoftwareToBe doorsState O: output results Output Devices (e.g actuators) SysReq ⊆ M × C relation on environment monitored/controlled variables SofReq ⊆ I × O relation on software input/output... phenomena (holds regardless of any software -to- be) trainAcceleration > 0 → trainSpeed ≠ 0 Assumption: statement to be satisfied by the environment of the Assumption software -to- be – formulated in terms of environment phenomena – generally prescriptive (e.g on sensors or actuators) measuredSpeed ≠ 0 iff trainSpeed ≠ 0 Definition: statement providing a precise meaning to system Definition concepts or... TrainMoving → DoorsClosed Further to requirements, we need to elicit, evaluate, document, consolidate relevant assumptions & domain properties www.wileyeurope com/college/van lamsweerde Chap.1: Setting the Scene © 2009 John Wiley and Sons 23 Categories of requirements Functional requirements: prescribe what services the software -to- be should provide – capture intended software effects on environment,... com/college/van lamsweerde Chap.1: Setting the Scene © 2009 John Wiley and Sons 22 Mapping system reqs to software reqs involves satisfaction arguments SOFREQ, ASM, DOM |= SysReq “If the software requirements in SOFREQ, the assumptions in ASM and the domain properties in DOM are all satisfied and consistent, then the system requirements SysReq are satisfied” SofReq: ASM: measuredSpeed ≠ 0 → doorsState = 'closed’ . Sons 0!, ! *23 4 *20 4 *2# Objectives *23 *23 + *20 *20 &+ *2# *2# $ $ !+ satisfy assignment requirements, constraints, assumptions problems, problems, opportunities, opportunities, system knowledge system knowledge System- to- be System- as-is 14 www.wileyeurope. Sons 0!$&&& ,! $ ( ( (,$!!$ ( ($ ($,!$!!! System- as-is as-is Concepts, phenomena, rules about car handbraking System- to- be to- be Machine Concepts, phenomena, rules about automated handbraking Car Driver Brake 10 www.wileyeurope. '4!!! World Machine MotorRaising HandbrakeReleased DriverWantsToStart motor.Regime = ‘up’ handBrakeCtrl = ‘off’ errorCode = 013 Machine Machine phenomena phenomena World World phenomena phenomena Shared Shared phenomena phenomena stateDatabase updated 9 www.wileyeurope