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Requirements Management - I

Lecture # 18

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Requirements Engineering Process

RequirementsElicitation

RequirementsAnalysis andNegotiation

RequirementsSpecification

RequirementsValidation

User Needs, Domain Information,

Existing System Information, Regulations,

Standards, Etc.

RequirementsDocument

Agreed Requirements

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Requirements Management and

Traceability

• Requirements cannot be managed

effectively without requirements traceability– A requirement is traceable if you can discover

who suggested the requirement, why therequirement exists, what requirements arerelated to it and how that requirement relates toother information such as systems designs,implementations and user documentation

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Change - A Constant

• There is nothing permanent except change
  • Heraclitus (500 B.C.)
    • No matter where you are in the system life

cycle, the system will change, and the desireto change it will persist throughout the lifecycle

• Software is like a sponge due to its

susceptibility to change

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Changing Requirements - 2

• A major issue in requirements engineering

is the rate at which requirements changeonce the requirements phase has “officially”ended

• This rate is on average 3% per month in the

subsequent design phase, and should godown after that

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Changing Requirements - 3

• This rate should come down to 1% per

month during coding

• Ideally, this should come down to no

changes in testing, however, this isvery rare

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Sources of Change - 2

• Reorganization or business

growth/downsizing causes changes inproject priorities or softwareengineering team structure

• Budgetary or scheduling constraints

cause a redefinition of the system orproduct

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Why All This Modification?

• As time passes, all constituencies know

more– About what they need– Which approach would be best– How to get it done and still make money

• Statement of the fact: most changes are

justified!

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Main Concerns in Requirements

Management

• Managing changes to agreed requirements• Managing the relationships between

requirements

• Managing the dependencies between the

requirements document and otherdocuments produced in the systemsengineering process

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CASE Tools for Requirements

Management

• Requirements management involves the

collection, storage and maintenance of largeamounts of information

• There are now a number of CASE tools

available which are specifically designed tosupport requirements management

• Configuration management tools may be

adapted for requirements engineering

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Stable and Volatile Requirements

• Stable requirements are concerned with the

essence of a system and its applicationdomain. They change more slowly thanvolatile requirements

• Volatile requirements are specific to the

instantiation of the system in a particularenvironment and for a particular customer

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Requirements Change Factors - 1• Requirements errors, conflicts and

inconsistencies

• Evolving customer/end-user

knowledge of the system

• Technical, schedule or cost problems

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Evolving Customer/End-user

Knowledge of the System

• As requirements are developed,

customers and end-users develop abetter understanding of what theyreally require from a system

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Technical, Schedule or Cost

Problems

• Problems may be encountered in

implementing a requirement. It may betoo expensive or take too long toimplement certain requirements