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8/12/2019 0721499 - Lecture 7 - Requirements Engineering
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Lecture 7: Requirements Engineering
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Waterfall Model
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The Requirement Engineering
Process The process of establishing what services are required and the
constraints on the systems operation and development
Requirements engineering help software engineers to better
understand the problem they will work to solve. It encompassesthe set of tasks that lead to an understanding of what thebusiness impact of the software will be, what the customer wantsand how end-users will interact with the software.
Requirement Engineering Process Feasibility Study
Requirements elicitation and analysis
Requirements Specification
Requirements Validation
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The Requirements Engineering
Process
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Requirements Elicitation It is the practice of obtaining the requirements of a system from
users, customers and other stakeholders. The practice is alsosometimes referred to as Requirement gathering.
Requirements elicitation practice include the following: Interviews Questionnaires User observation Workshops
Brain storming Use cases Role playing And prototyping
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Requirements Elicitation Problems of Requirement Elicitation
Problems of scope:The boundary of system is ill-defined. Or unnecessary details are provided.
Problems of understanding:The users are not sure ofwhat they need, and dont have full understanding of theproblem domain.
Problems of volatility:the requirements changeovertime.
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Requirements Elicitation Guidelines of Requirements Elicitation
Assess the business and technical feasibility for the proposed system
Identify the people who will help specify requirements.
Define the technical environment (e.g. computing architecture, operating
system, telecommunication needs) into which the system or product willbe placed
Identify domain constraints (i.e. characteristics of the businessenvironment specific to the application domain) that limit thefunctionality or performance of the system or product to build
Define one or more requirements elicitation methods (e.g. interviews, team
meetings, ..etc) Solicit participation from many people so that requirements are defined
from different point of views.
Create usage scenarios of use cases to help customers/ users better identifykey requirements.
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Requirements Analysis Requirements Analysis, determining whether the
stated requirements are clear, complete, consistentand unambiguous.
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Requirements Analysis Stakeholder Identification
Stakeholders are people or organizations that have avalid interest in the system. They may be affected by itdirectly or indirectly.
Stake holders may include:
Anyone who operates the system
Anyone who benefits from the system
Anyone involved in purchasing or procuring the system
People opposed to the system (negative stakeholders)
Organizations responsible for the system
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Requirements Analysis Stakeholder Interviews
Interviews are a common technique used in requirementanalysis.
This technique can serve as a means of obtaining thehighly focused knowledge from different stakeholdersperspectives
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Requirements Analysis Types of Requirements:
Customer Requirements: Operational distribution or deployment: Where will the system be
used?
Mission profile or scenario: How will the system accomplish itsmission objective? Performance and related parameters: What are the critical system
parameters to accomplish the mission? Utilization environments: how are the various system components to
be used?
Effectiveness requirements: How effective or efficient must thesystem be in performing its mission? Operational life cycle: How long will the system be in use by the
user? Environment: what environments will the system be expected to
operate in an effective manner?
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Requirements Analysis Types of Requirements:
Architectural Requirements:
A formal description and representation of a system,organized in a way that support reasoning about the structureof the system which comprises system components, theexternally visible properties of those components, therelationships and the behavior between them, and provides aplan from which products can be procured and systems
developed, that will work together to implement the overallsystem.
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Requirements Analysis Types of Requirements:
Functional Requirements:
Defines functions of a software system or its components.They may be calculations, technical details, datamanipulation and processing and other specific functionalitythat define what a system is supposed to accomplish?
They describe particular results of a system.
Functional requirements are supported by Non-functionalrequirements.
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Requirements Analysis Types of Requirements:
Non-Functional Requirements:
They are requirements that specify criteria that can be used to judge
the operation of a system, rather than specific behavior. Functional requirements define what the system is supposed to do,
whereas non-functional requirements define how a system issupposed to be.
Non-functional requirements can be divided into two main
categories: Execution qualities, such as security and usability, which are
observable at runtime.
Evolution qualities, such as testability, maintainability and scalability.
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Requirements Specifications Requirements Specification is the direct result of a
requirement analysis and can refer to:
Software Requirements Specification
Hardware Requirements Specification
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Requirements SpecificationsA Software Requirements Specification (SRS) a
requirements specification for a software system is acomplete description of the behavior of a system to bedeveloped. It includes a set of use cases that describeall the interactions the users will have with thesoftware. In addition to use cases, the SRS alsocontains non-functional requirements (such as
performance requirements, quality standards, ordesign constraints)
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Requirements Specifications A Software Requirements Specification (SRS)
The software requirement specification document enlists allnecessary requirements for project development. To derive therequirements we need to have clear and thorough understanding of
the products to be developed. A general organization of an SRS is as follows:
Introduction Purpose, Scope, Definitions, System Overview, References
Overall Description Product Perspective, Product functions, User characteristics,
constraints, assumptions and dependencies. Specific Requirements
External Interface requirements, functional requirements,performance requirements, design constraints, logical databaserequirement, software system attributes.
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Requirements Validation and
VerificationValidation (& Verification), is the process of checking
whether the requirements, as identified, do notcontradict the expectations about the system ofvarious stakeholders and do not contradict each other.
It is Requirements Quality Control
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Validation Vs. VerificationValidation: Am I building the right product?
checking a work product against higher-level workproducts or authorities that frame this particular
product. Requirements are validated by stakeholders
Verification: Am I building the product right?
checking a work product against some standards andconditions imposed on this type of product and theprocess of its development. Requirements are verified by the analysts mainly
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More about validation Requirements validation makes sure that requirements
meet stakeholders goals and dont conflict with them.