Software Development

Module Code: CST 240

Chapter 3: Requirement Analysis

Dr. Husam Osta

2013

Outline• Requirements Engineering• Functional/non-functional requirements• Feasibility study• Requirements elicitation and analysis • Requirements validation• Requirements management C

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Requirements Engineering

• The process of eliciting, analysing, documenting, and validating the services required of a system and the constraints under which it will operate and be developed.

• Descriptions of these services and constraints are the requirements for the system.

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Requirements Engineering

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Involves a variety of people in an organization, such as:

• System end users and their managers.

• Engineers who are developing or maintaining other related systems.

• Trade union representatives.

• Others in the organization who will be affected by the system.

• All of the above are called stakeholders

Requirements engineering

• Requirements engineering is a difficult process because:• Stakeholders make unrealistic demands. • Requirements are expressed in stakeholders

language• Different requirements from different stakeholders• Political factors• Analysis Environment

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Software System Requirement

• Software System Requirements can be classified as • Functional Requirement:

are the services the system should provide and what the software should do.

• Nonfunctional Requirement: arise through user needs, because of budget constraints, because of organizational policies, because of the need for interoperability with other software or hardware systems, or because of external factors such as safety regulations or privacy legislation.

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Types of Non-functional requirements

• Product requirements – specify product behaviour.

• Organizational requirements – derived from policies / procedures in customer’s or developer’s organization (e.g., process constraints).

• External requirements – derived from factors external to the product and its development process (e.g., interoperability requirements, legislative requirements). C

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Non-Functional ClassificationsNon-Functional Classifications

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Performancerequirements

Spacerequirements

Usabilityrequirements

Efficiencyrequirements

Reliabilityrequirements

Portabilityrequirements

Interoperabilityrequirements

Ethicalrequirements

Legislativerequirements

Implementationrequirements

Standardsrequirements

Deliveryrequirements

Safetyrequirements

Privacyrequirements

Productrequirements

Organizationalrequirements

Externalrequirements

Non-functionalrequirements

Performancerequirements

Spacerequirements

Usabilityrequirements

Efficiencyrequirements

Reliabilityrequirements

Portabilityrequirements

Interoperabilityrequirements

Ethicalrequirements

Legislativerequirements

Implementationrequirements

Standardsrequirements

Deliveryrequirements

Safetyrequirements

Privacyrequirements

Productrequirements

Organizationalrequirements

Externalrequirements

Non-functionalrequirements

Examples of non-functional requirements

• Product requirement:4.C.8 It shall be possible for all necessary communication between the system and the user to be expressed in the standard Ada character set.

• Organisational requirement:9.3.2 The system development process and deliverable documents shall adapt to the process and deliverables defined in XYZCo-SP-STAN-95.

• External requirement:7.6.5 The system shall not disclose any personal information about customers apart from their name and reference number to the operators of the system.

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Difference between functional and non functional requirements Sl.No Functional Requirement Non-functional Requirement

1.Defines all the services or functions required by the customer that must be provided by the system

Defines system properties and constraints e.g. reliability, response time and storage requirements. Constraints are I/O device capability, system

representations, etc .

2.It describes what the software should do.It does not describe what the software will do, but how the software will do it .

3.Related to business. For example: Calculation of order value by Sales Department or gross pay by the Payroll Department

Related to improving the performance of the business. For example: checking the level of security. An operator should be allowed to view only my name

and personal identification code .

4.Functional requirement are easy to test .Nonfunctional requirements are difficult to test

5.Related to the individual system features Related to the system as a whole

6.Failure to meet the individual functional requirement may degrade the system

Failure to meet a non-functional requirement may make the whole system unusable .

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Requirements Engineering Processes

• The processes used for RE vary widely depending on the application domain, the people involved and the organization developing the requirements.

• However, there are a number of generic activities common to most processes:• Feasibility study• Requirements elicitation (collection) and analysis• Requirements validation

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Role of the feasibility study

• Identify alternatives • Analyse costs and benefits• Establish priorities• Present alternatives

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Feasibility study• Determines whether or not the proposed undertaking

is worthwhile.

• Aims to answer three basic questions:1. Would the system contribute to overall organizational

objectives?2. Could the system be engineered using current technology

and within budget?3. Could the system be integrated with other systems

already in use?

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Types of feasibility

1.1. Operational FeasibilityOperational Feasibility2.2. Technical FeasibilityTechnical Feasibility3.3. Schedule FeasibilitySchedule Feasibility4.4. Economic FeasibilityEconomic Feasibility

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Types of feasibility1. Operational Feasibility

• Identify how complex is the problem and check if the given solution will solve the problem.

• It involves the analysis of:1. Performance (throughput, reliability, response time, and process

improvement).2. Control (security and protection against fraud).3. Efficiency : does the system make maximum use of available

resources.4. Ease of use and ease of learning.

– Will the solution fulfils the users’ requirements? To what degree?– How will the solution change the users’ work environment?– How do users feel about such a solution?

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Types of feasibility2. Technical Feasibility

• Is the proposed technology or solution practical?• State-of-the-art (High-tech) technology vs. mature (old)

technology.• Do we currently possess the necessary technology?• Do we possess the necessary technical expertise?

3. Schedule Feasibility• Given the current technology and technical expertise, are the

project deadlines reasonable?• What happens if we don’t finish on time?

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Types of feasibility4. Economic Feasibility

• Is the proposed system cost-effective?• What is the return-on-investment (ROI)? [ROI measures the magnitude of the benefits relative to the costs ]• What is the break-even point?

[Break-even point is the time from the first money spent until the development investment has been recovered. ]

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The Requirement elicitation (collection) and analysis process

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The Requirement elicitation and analysis process1. Domain understanding: develop an

understanding of the application domain. Involves working with stakeholders to learn about the application domain, the services needed and the system’s operational constraints

2. Requirements collection: the process of interacting with the stakeholders to discover requirements.

3. Classification: organize the unstructured collection of requirements into coherent clusters.

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The Requirement elicitation and analysis process

4. Conflict resolution: finding and resolving conflicted requirements.

5. Prioritization: interacting with the stakeholders to discover the most important requirements.

6. Requirements validation: requirements are checked to discover if they are complete, consistent, and in accordance with what the stakeholders want from the system.

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Requirements DiscoveryRequirement discovery is the formal process of collecting

information about problems, requirements, and preferences. It is also called information gathering or fact finding.

The different fact finding techniques include1- Observation: 2- Interviewing: 3- Questionnaires:4- Searching:.5- Sampling:

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Requirements Discovery- Observation• Observation is a fact-finding technique wherein the systems analyst

either participates in or watches a person perform activities to learn about the system.

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Requirements Discovery - InterviewsWhom to interviewA. Top level managers

• To confirm project team understanding of the business.• To get commitment for the project.

B. Middle level managers• To obtain greater understanding of the problem.• To define the requirements in general terms.

C. Operational managers• To get a full more detailed information of the problem.• To obtain the critical points about the work procedures.

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Requirements Discovery – Interview types1. Unstructured interviews

• Informal, the interviewer develops the theme of the interview according to the answers.

• It is in the format of questions and answers.• Used when the analyst wants to get general information about the

business.

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Requirements Discovery – Interview types

2. Structured interviews• Uses standardized predefined questions in either open response or

dead response format.• Uses a set of prescribed answers.• Used when the analyst wants to get full details about the business.

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Requirements Discovery – Questionnaires• They are sets of predefined and standardized questions arranged on

a form to obtain information about a particular subject.• They are used for:

• Evaluating specific features of a system.• Investigate different opinions, knowledge, or attitudes towards

the system.• They are sent via: mail, fax, e-mail, or in-person.

• They should be made easy for the user to complete because:• If the user find the questions difficult, they might not complete

the questionnaire, which will result in low rate of return.• Avoid ambiguity, because ambiguous questions generate

unreliable answers.

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Requirements Discovery – Types of Questions

• Open Ended [Free Format]• Close ended [Fixed Format ]• Mixed

• Open ended (or free format) : There is no predefined answers

• Example:

What types of computers do you currently have installed?name model qty

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Requirements Discovery – Types of Questions

• Close Ended [Fixed format ]• Example:

• Multiple choice:

Which of the following cities would you like to live in?a)New Yorkb)Londonc)Parisd)Rome

• RatingDo you feel this class is important?

a) Strongly agree b) Agree c) No opinion d) disagree e) strongly disagree

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Requirements Discovery – Types of Questions

• Mixed• Example:

In what type of business is your organization?1) Government 4) Trading2) Military 5) Others ( please specify)3) Industrial ____________________

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InterviewQuestionnaireInterviews are conducted only with selected persons. Hence addresses a small group of people.

Address a large crowd

Probing and follow-up is easyLimited probing and follow-up done after collection of original data.

Interviewee is known to the interviewer

Respondents can be unknown

Unclear questions can be clarified by both the interviewer and the interviewee.

Unclear questions may not be clarified which my result in misunderstanding and wrong answers.

The information obtained will be rich.

The information may not be so rich.

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Requirements Discovery - Searching

• All available written material that describes the business should be considered. In addition the documents that provide information should be catalogued for future reference.

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Requirements Discovery - Searching

There are 3 groups of documents:

A. Business documents• Annual reports, business plans and forecasting,

organization chart, hand books, and advertising booklets.

B. Current system environment documents• System description, data administration

guidelines, system architecture documents, system flowcharts, database specifications, IT organizational chart, user manual.

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Requirements Discovery - Searching

C. Current technical environment documents• Hardware distribution list, capacity planning

documents, system software list, network documents, performance statistics, hardware and software plans.

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Requirements Discovery - Sampling• Sampling is the process of collecting a representative

sample of documents, forms, and records. • Randomization is a sampling technique characterized

as having no predetermined pattern or plan for selecting sample data.

• Stratification is a systematic sampling technique that attempts to reduce the variance of the estimates by spreading out the sampling—for example, choosing documents or records by formula—and by avoiding very high or low estimates.

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Viewpoint-oriented analysis• For every system there are a group of stakeholders and each group

has different interest in the system, each interest is called a viewpoint.

• To illustrate viewpoints lets take the example of ATM stakeholders

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ATM stakeholders• Bank customers• Representatives of other banks• Bank managers• Counter staff• Database administrators • Security managers• Marketing department• Hardware and software maintenance engineers• Banking regulators

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Viewpoint-oriented analysisAny viewpoint may be considered as:1. A data source or sink

• In this case the analyst must identify what data is produced or consumed and what is the process of doing that.

• A cross-check is made to discover data being produced but not consumed or vice versa.

• Used by the CORE method.

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Viewpoint-oriented analysis2. A representation framework

• In this case, each viewpoint is represented by a different data model.

• The data models are cross-checked to discover requirements that would be missed.

• Used by the VOSE method

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Requirement Validation• Requirements validation is an activity that checks the

requirements definition document for accuracy, completeness, consistency, and conformance to standards.

• Concerned with whether or not the requirements define a system that the customer really wants.

• Requirements error costs are high, so validation is very important.

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Requirements checking• Validity. Does the system provide the functions which

best support the customer’s needs?• Consistency. Are there any requirements conflicts?• Completeness. Are all functions required by the

customer included?• Realism. Can the requirements be implemented given

available budget and technology• Verifiability. Can the system be tested to determine

whether or not the requirements are met?

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Requirements validation techniques• Requirements reviews / inspections – systematic manual analysis of

the requirements.• Prototyping – using an executable model of the system to check

requirements. • Test-case generation – developing tests for requirements to check

testability.• Automated consistency analysis – checking the consistency of a

structured requirements description.

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Requirements management• Requirements management is the process of managing changing

requirements during the requirements engineering process and system development.

• New requirements emerge during the process as business needs change and a better understanding of the system is developed.

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Requirements management• The priority of requirements from different viewpoints changes

during the development process.• The business and technical environment of the system changes

during its development.

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Requirements change management

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