Software Requirements Software Requirements and Designand Design

Khalid IshaqKhalid Ishaq

Overview

• The requirements Problem• Requirements Management• Analyzing Problems• Understanding the Users Needs• Defining and Refining the System• Managing Scope

The Requirements Problem

• “The goal of software development is to develop quality software – on time and on budget – that meets customers’ real needs.” To obtain this goal we must know:– “Exactly what is the software supposed

to do?”– “How do we know that the software is

doing exactly that and nothing else?”

Root Causes of Project Failure

• Requirement errors are the most common type of systems development error and the most costly to fix.

Root Causes of Project Failure

• Data (Standish Group 1994 )– $250 Billion each year on 175,000 IT projects.– Average Cost:

• Large Projects: $2,322,000• Medium: $1,331,000• Small: $434,000

• 31% will be cancelled before they are completed or loss of $81 Billion

• 52.7% will cost 189% of the original estimate or loss of $59 Billion

Root Causes of Project Failure

• Requirements Related– Lack of user input: 13% of all projects– Incomplete requirements and

specifications 12% of projects– Changing requirements and

specifications 12%

Root Causes of Project Failure

• Non-Requirements Related– Unrealistic schedules 4%– Inadequate staffing 6%– Inadequate technology skills 7%

Root Causes of Project Failure

• Source: European Software Process Improvement Training Initiative (ESPITI) 3800 responses– 2 largest Problems in ½ the responses

• Req. specifications• Managing customer requirements

Root Causes of Project Failure

• 1/3 of projects fail due to requirements gathering, requirements documentation, or requirements management problems

Root Causes of Project Success

• Large companies 9% delivered on time and budget and for small 16%

Root Causes of Project Success

• User involvement 16%• Exec management support 14%• Clear statement of requirements

12%

Costs

• Relative Cost to Repair– Requirements time 0.1 – 0.2– Design 0.5– Coding 1– Unit Test 2– Acceptance Test 5– Maintenance 20

Costs

• Error that occurred when the development staff created the technical design from a correct set of requirements

Costs

• Error that leaked into the design phase due to wrong requirements.– By the time the req. error is detected,

design group has invested time and effort in a design

– Assumes the error is design related and takes a while to point to the wrong requirements.

Requirements Management

• What is a Requirement– A requirement is a capability that the

system must deliver

Requirements Management

• What is a Requirement Management– Requirements Management is a process of

systematically eliciting, organizing and documenting requirements for a complex system.

Requirements Management

• The skill to elicit useful and complete requirements from the users

• Since 100’s or 1000’s of req. may be associated with a system, organize them

• Documentation of the req. for effective communication among stakeholders

Eliciting Requirements

• Is this a nice-to-have or a must have?– Need or requirement– Statement of the problem or statement of the

solution– Goal of the system or a contractual requirement

Skills

• Analysis the problem• Understand the user needs• Defining the system• Managing scope• Refining the system• Building the right system

Problem Analysis

• Gain agreement on the problem definition

• Understand the root causes – the problem behind the problem

• Identify the stakeholders• Defining the solution system

boundary• Identify Constraints

The Problem Statement

• The problem of Describe the problem• Effects Identify the stake

holders affected by the problem

• The result of which Describe the impact of this problem on the

stakeholders and business activity

• Benefits of indicated the proposed solutions and list a few key benefits.

Root Causes

• Fishbone diagram • Standard Document

Stakeholders

• Users of the system• Customer (Buyer) of the system• Effected by the output of the system• Executives• Misc. Users• Maintainers• Unknown

Solution Boundary

• Our System• Outside interaction

Constraints

• Economics• Political• Technical• System• Environment• Schedule and Resources

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