Introduction to Requirement engineering

Introduction to Requirement engineering

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  Software Requirements analysis & specifications
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  Requirements Engineering • Theprocess of collecting the software requirement from the client then understand, evaluate and document it is called as requirement engineering. • Requirement engineering constructs a bridge for design and construction.
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  Requirements Engineering 1. Requirementengineering is the discipline concerned with understanding the externally imposed conditions on a proposed computer system, determining what capabilities will meet these imposed conditions and documenting those capabilities as the software requirements for the computer system. 2. The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed. 3. A requirement mandatesthat somethingbe accomplished,transformed, producedor provided. 3
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  Importance of Requirements •Makingdesigndecisionswithoutunderstanding allthe constraintsonthesystemtobedeveloped resultsina systemwhichfailstomeetcustomer’s expectations. • Costsofcorrectingerrorsincreasesasthedesign process advances. • Anerrordetectedinthemaintenancephaseis20 timesas costlytofixasanerrordetectedinthe codingstage.
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  Requirements Perspectives • Userrequirements Statements in natural language plus diagrams of the services the system provides and its operational constraints. Written for customers. • System requirements A structured document setting out detailed descriptions of the system’s functions, services and operational constraints. Defines what should be implemented so may be part of a contract between client andcontractor.
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  Types of Requirements 1.User requirements • Statements in natural language plus diagrams of the services the system provides and its operational constraints. • Written for customers. 2. System requirements • A structured document setting out detailed descriptions of the system’s functions, services and operational constraints. • Defines what should be implemented so may be part of a contract between client and contractor. • Whom do you think these are written for? • These are higher level than functional and non-functional requirements, which these may subsume. 6
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  Types of Requirements •Functionalrequirements: • Statementsof services,how the systemshould react to particular inputs, what functionalities isto beprovided. Functionalrequirements arenot concernedwith howthese functionsareto beachieved, just what isto beachieved. • Non–functionalrequirements: • dealswith attributes, or properties, of the software ratherthan functions.Weinclude hereaspectsof the • softwaresuchasits performance, its usability,itsreliability, anysafety aspectsandarangeof otherattributes. • DomainRequirements: • Requirementsof the applicationdomainof the system, reflect characteristicsof thatdomain.
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  Requirements Characteristics • Unambiguous •Testable (verifiable) • Clear(Concise,terse, simple, precise) • Correct • Understandable • Feasible • Independent • Atomic • Necessary • Implementation –free(abstract)
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  Requirements Characteristics Besides the criteriafor individual requirements, 3 criteria should apply to the set of requirements as a whole: • Consistent • Non redundant • Complete
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  Requirements engineering processes • The processesused for RE vary widely depending on the application domain, the people involved and the organisation developing the requirements • However, there are a number of generic activities common to all processes 1. Requirements elicitation 2. Requirements analysis 3. Requirements validation 4. Requirements management
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  Requirements Elicitation: It isrelated to the various ways used to gain knowledge about the project domain and requirements. The various sources of domain knowledge include customers, business manuals, the existing software of same type, standards and other stakeholders of the project. The techniques used for requirements elicitation include interviews, brainstorming, task analysis, Delphi technique, prototyping, etc. Elicitation does not produce formal models of the requirements understood. Instead, it widens the domain knowledge of the analyst and thus helps in providing input to the next stage.
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  Requirements specification: This activityis used to produce formal software requirement models. All the requirements including the functional as well as the non-functional requirements and the constraints are specified by these models in totality. During specification, more knowledge about the problem may be required which can again trigger the elicitation process. The models used at this stage include ER diagrams, data flow diagrams(DFDs), function decomposition diagrams(FDDs), data dictionaries, etc.
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  Requirements verification andvalidation: Verification: It refers to the set of tasks that ensures that the software correctly implements a specific function. Validation: It refers to a different set of tasks that ensures that the software that has been built is traceable to customer requirements. If requirements are not validated, errors in the requirement definitions would propagate to the successive stages resulting in a lot of modification and rework. The main steps for this process include: • The requirements should be consistent with all the other requirements i.e no two requirements should conflict with each other. • The requirements should be complete in every sense. • The requirements should be practically achievable.
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  The Output ASoftwareRequirements Specification(SRS)–Aformal Document as the OUTPUToftheSpecificationstage. • Itis a completedescription ofthe behaviorofasystem developedthat includes: • Functional Requirements • Non- Functional Requirements Constraints • DesignStrategy Qualityand Standards Architecture • DevelopmentMethodology
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  Analysis &Specification • Requirementsanalysis: • Theprocessof studying and analysingthe customer and the user/stakeholder needstoarrive at adefinition of software requirements • RequirementsSpecification: • Adocument that clearly and precisely describes essential requirements of softwareand external interfaces (functions, performance, qualityetc.) • eachrequirement isspecified suchthat its achievement is capableof being verified bya prescribed method like inspection,test.
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  Requirement Engineering isthe process characterized for achieving following goals- • Understanding customer requirements and their needs • Analyzing the feasibility of the requirement • Negotiating the reasonable solutions • Specification of an unambiguous solution • Managing all the requirement • Finally transforming the requirements of the project Requirement engineering consists of seven different tasks as follow: 1. Inception 2. Elicitation 3. Elaboration 4. Negotiation 5. Specification 6. Validation 7. Requirements Management Requirements Engineering Tasks