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CSC-3324: Chapter 5

Requirements Engineering

Reading: Chap. 6, 7 + annex

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Wrap up on Chap. 1, 2, 3 & 4...

What is Software Engineering (SE) ?

The major goal of SE is to produce good software

cost effectively… What is good software?

In order to produce good software, we need to

follow a good SE process… What is a good process?

Some SE process models are widely used and

universally recognized…

Before launching any SE process, we should first be

perform a feasibility study...

Software engineering is concerned with theories, methods and tools for professional software development

Maintainability, Dependability,

Efficiency, Usability

Understandable, Visible, Supported, Accepted, Reliable,

Rapid, etc.Structured set of activities

(steps) required to develop a software system....

The waterfall model

Separate and distinct phases of specification and

development

Prototyping development

Specification and development are interleaved

Component-based development

The system is assembled from existing components

A quick and cheap study of the project requirements in order to assess the business

opportunity, the technology enablers and the schedule...

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Wrap up on Chap. 1, 2, 3 & 4...

Now we are ready to launch the Requirements

Engineering process…

Three kinds of Requirements...

Common problems in Requirements gathering...

Requirements must be documented…

Requirements Gathering is an iterative process

by its nature…

An attribute that the projected system

must fulfill…User Requirements,

System Requirements and Requirements specifications

Precision, Completeness and Consistency...

Functional, Non Functional and Domain relatedAnalysis and Requirements

Elicitation/Gathering overlaps...

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Requirements Engineering...

The process of establishing the services that the customer requires from a system and the constraints under which it operates and is developed...

The requirements themselves are the descriptions of the system services and constraints that are generated during the requirements engineering process….

Engineering consists of collecting, analyzing, discovering and documenting the requirements in order to better understand and (Re)Present them...

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How to ?

There are a number of generic and

mandatory activities to carry out: Requirements elicitation...

Requirements analysis...

Requirements validation...

Requirements management...

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The Conceptual Analysis Process

Feasibilitystudy

Requirementselicitation and

analysisRequirementsspecification

Requirementsvalidation

Feasibilityreport

Systemmodels

User and systemrequirements

Requirementsdocument

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The Requirements Definition Document...

Collecting...+ Analyzing...+ Validation with the Client...

+ Specifying them in a written document

Requirements Document: (U.S.R+ models of Data, Processes & Users)…

Must be understood by the client…

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KettaCar’s User and System Requirements (U.S.R)

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System models

Different models may be produced during

the requirements analysis activity...

Requirements analysis may involve three

structuring activities which result in these

different models

System models will be developed using

Merise method...

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System Analysis... Consist of Decomposing, Understanding entities

and processes of the current system, and

recomposing the whole system in a better way…

It focuses on: Processes… (Conceptual Process Model) Data… (Conceptual Data Model) Users… (Interface Model)

Usually we start by drawing a global architecture

of the system… The conceptual flow diagram

Based on Merise

Method...

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The first step: The Conceptual Flow Diagram

In order to understand the current system, its

boundaries must be established to determine what

must be implemented...

These are documented using a description of the

system context in term of Users, Data, Processes…

The Conceptual Flow Diagram is a global picture

that presents an abstract view of the components

(data, users and processes) making up a system...

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The first step: The Conceptual Flow Diagram

The Conceptual Flow Diagram must include

major information flows between sub-systems...

Must identify different types of functional

component in the model...

Usually presented as a block diagram...

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KettaCar Conceptual Flow Diagram

In Merise, we use the Context diagram to

present the Conceptual flow diagram…

See the annex given in the class

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KettaCar Context Diagram

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An exampl

e of CPM

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http://perso.wanadoo.fr/matthieu.vidal/default.htm

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The conceptual Architecture...

It is directly derived from the context diagram and the different CPMs…

The hierarchy of processes in the CPM… The leafs of your architecture are the

slots where to write algorithms during the design time…

DFDs are obtained from the CPM...

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Conceptual Architecture of KettaCar...

See the annex given in the class

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Conceptual Data Modeling… See annex SE-CDM…

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From the CDM to the E/R model

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Putting data and Processes together...

The goal of confronting data and processes is to ensure that: All the necessary data is available for

the processes… There is no data that appear in the

CDM but is used by none of the processes...

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KettaCar case... See the annex...

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Requirements validation

Concerned with demonstrating that the

requirements define the system that the

customer really wants

Requirements error costs are high so validation is

very important

Fixing a requirements error after delivery may cost up to

100 times the cost of fixing an implementation error

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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 requirements be checked?

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Requirements validation techniques

Requirements reviews 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 reviews

Regular reviews should be held while the

requirements definition is being formulated

Both client and contractor staff should be

involved in reviews

Reviews may be formal (with completed

documents) or informal. Good communications

between developers, customers and users can

resolve problems at an early stage