Requirements Engineering Essay Example

Requirements Engineering Essay Example Requirements Engineering Essay Requirements Engineering Essay Pressman, Mc-Graw Objects, Components and Frameworks with UML, D. DSouza, A. Wills, Addison-Wesley, 1999 Winter Term 2010/11 Slide 3 Sven Apel Software Engineering Roadmap Requirements-engineering process Use cases Functional and non-functional requirements Requirements checking and reviews Roles in requirements engineering Slide 4 Zeitschema Kommission: Bitte ankreuzen wo Sie keinenfalls mitmachen k? ¶nnen, und senden Sie das ausgef?llte Formular bis 7 8:00 9:00 10:oo ll:oo 12:00 ans Dekanat zur?ck. 4:00 1 5:00 16:00 17:00 Jan 2002 1011 12131415161718192021 22232425262728293031 Feb 2002 56 13:00 18:00 Bemerkungen: Unterschrift: Slide 5 Electronic Time Schedule So, basically we need a form for the time schedule that can be distributed by e-mail, a place (html) where I can deposit these forms after they have been filled out, and an algorithm that calculates a few possible meeting times, possibly setting priorities to certain persons of each committee (since there will always be some time schedule overlaps). It would also be great if there were a way of checking whether everybody of the relevant committee has really sent their time schedule back and at the same time isting all the ones who have failed to do so. An automatic invitation letter for the committee meeting to all the persons involved, generated through this program, would be even a further asset. How can we transform this description into a requirements specification? Winter Term 2010/11 Slide 6 The Requirements-Engineering Process Ian Sommerville 2000 Slide 7 Requirements-Engineering Activities Feasibility study Requirements elicitation analysis Determine if the user needs can be satisfied with the available technology and budget. Find out what system stakeholders require trom he system. specification Define the requirements in a form understandable to the customer and as a contract between client and contractor. validation Check the requirements for realism, consistency, and completeness. Requirements are for users; specifications are for analysts and developers. Slide 8 Requirements Elicitation Analysis Sometimes called requirements discovery Technical staff work with customers to determine 0 the application domain, 0 the services that the system should provide and 0 the systems operational constraints. Involves various stakeholders: 0 e. g. end-users, managers, engineers involved in maintenance, domain experts, trade unions, etc. Slide 9 Problems ot Requirements Analysis Various problems typically arise: Stakeholders dont know what they really want 0 Stakeholders express requirements in their own terms 0 Different stakeholders may have conflicting requirements 0 Organisational and political factors may influence the system requirements 0 The requirements change during the analysis process. 0 New stakeholders may emerge. Slide 10 How the Customer explained it How the Project Leader understood it How the Analyst designed it What the Customer really needed Slide 11 Requirements Evolution Requirements always evolve as a better understanding of user needs is developed and as the organisations objectives change It is essential to plan for change in the requirements as the system is being developed and used Slide 12 Requirements Analysis, Specification, and Validation O Ian Sommerville 2000 Slide 13 Slide 14 Sottware Engineering Use Cases and Scenarios A use case is the specification of a sequence of actions, including variants, that a system (or other entity) can perform, interacting with actors of the system. g. , buy a DVD through the Internet A scenario is a particular trace of action occurrences, starting from a known initial state. e. g. , connect to myDVD. com, go to the search page Slide 15 Unified Modeling Language UML is the industry standard for documenting object-oriented models Class Diagrams visualize logical structure of system in terms of classes, objects, and relationships Use Case Diagrams show external actors and use cases they participate in Sequence Diagrams visualize temporal message ordering of a concrete scenario of a use case Collaboration (Communication) Diagrams State Diagrams visualize relationships of objects exchanging messages in a concrete scenario specify the abstract states of an object and the transitions between the states Slide 16 More on this later Slide 17 Slide 18 Writing Requirements Definitions Requirements definitions usually consist of natural language, supplemented by (e. g. , UML) diagrams and tables. Three types of problems can arise: 0 Lack of clarity: It is hard to write documents that are both precise and easy-to-read. 0 Requirements confusion: Functional and non-functional requirements tend to be inte Requirements amalgamation: Several different requirements may be expressed together. Slide 19 Prototyping The objective of evolutionary prototyping is to deliver a working system to end-users. Must be used for systems where the specification cannot be developed in advance. 0 Development starts with the requirements that are best understood. The objective of throw-away prototyping is to validate or derive the system requirements. The prototype is developed from an initial specification, delivered for experiment then discarded 0 Prototyping starts with that requirements that are poorly understood. Slide 20