Requirements Analysis-Software Engineering-Lecture 02 Slides-Computer Science, Slides of Software Engineering

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LECTURE 2: REQUIREMENTS

Software Engineering

1 Requirements Analysis and Spec

• Involves: - feasibility study; - requirements analysis; - requirements definition; - requirements validation; - requirements specification.
• Aim: to establish derive a complete, official statement of what developers are required to do:

The software requirements document.

2 Requirements Analysis

The role of the analyst is:

• To elicit requirements.
• To resolve different views.
• To advise on what is feasible.
• To clarify requirements.
• To document requirements.
• To negotiate and gain user’s agreement for the spec.

2.1 How to Get Requirements

• Talk to the user: - listen to needs; - ask for clarification; - record the views.
• Clarify views: - resolve inconsistencies; - generate a consensus.
• Important to involve all the stakeholders.

2.3 Requirements Definition

• Requirements definition is:

High-level, customer-oriented statement of what system is to do.

• Should be accessible to all stakeholders.
• Two types of requirements: - functional: services the system should provide, how it should respond to inputs, how it should behave, what it should not do; “The system should then display all the titles of books written by the specified author.” - non-functional: constraints the system should operate under; “Should be implemented on a Pentium 450 with 64MB of RAM and 2GB hard disk.”

• Should be: - complete: document all services to be provided; - consistent: not be contradictory. - structured: not thrown together! - systematic: include evidence of organisation. - free of implementation bias: not mandate a solution.
• Use of natural language leads to 3 key problems: - lack of clarity; - requirements confusion; - requirements amalgamation.

• Reliability: - mean time to failure; - availability.
• Robustness: - time to restart after failure; - percentage of events causing failure; - freedom from data corruption on failure.
• Portability: - percentage of target-dependent statements; - number of target systems.

2.5 Kinds of Requirements

• Physical environment: - where is the equipment to function? - is there one location or several? - are there any environmental restrictions (temperature, humidity... )?
• Interfaces: - is the input coming from one or more other systems? - is the input going to one or more other systems? - is there a prescribed medium that data comes in/goes out as (e.g., floppy disk, CD ROM)?

• Documentation: - how much documentation is required? - to what audience is the document addressed? - what help features must be provided?
• Data: - what format should input/output data have? - how often will it be received or sent? - how accurate must it be? - to what degree of precision must calculations be carried out to? - how much data flows through the system? - must any data be retained?

• Security: - must access to the system be controlled? - how will one user’s data be isolated from another’s? - how often will the system be backed up? - must backup copies be stored at a separate location? - should precautions be taken against fire & theft?
• Quality assurance: - what are the requirements for reliability? - what is the mean time between failure? - what faults is the system required to catch?

3.1 Part 1: Introduction

1. Introduction

1.1 Purpose 1.2 Scope 1.3 Definitions, acronyms, abbreviations 1.4 References 1.5 Overview

3.2 Part 2: General Description

2. General Description

2.1 Product perspective 2.2 Product functions 2.3 User characteristics 2.4 General constraints 2.5 Assumptions and dependencies

3.2 External interface requirements

3.2.1 User interfaces 3.2.2 Hardware interfaces 3.2.3 Software interfaces 3.2.4 Communications interfaces

3.3 Performance requirements

3.4 Design constraints

3.5 Attributes

3.5.1 Security 3.5.2 Maintainability

3.6 Other requirements