CS8494 Software Engineering
UNIT – 2
REQUIREMENTS ANALYSIS AND SPECIFICATION
UNIT II REQUIREMENTS ANALYSIS AND SPECIFICATION
Software Requirements:
Functional and Non-Functional
User requirements
System requirements
Software Requirements Document
Requirement Engineering Process:
Feasibility Studies
Requirements elicitation and analysis
requirements validation
requirements management
Classical analysis:
Structured system Analysis
Petri Nets
Data Dictionary.
Requirement Types:
•User Requirements
•System requirements
•Functional Requirements
•Non-functional Requirements
•Domain Requirements
1.Software Requirements
•Functional Requirements
•Non-Functional Requirements
1.a.Functional Requirements
•Functional aspect of software
Examples -
•Search option given to user to search from various invoices.
•User should be able to mail any report to management.
•Users can be divided into groups and groups can be given separate
rights.
Non-Functional Requirements
•Not related to functional aspect of software
Non-functional requirements include -
•Security
•Storage
•Cost
•Flexibility
•Disaster recovery
•Accessibility
1.b.User Interface requirements
A software is widely accepted if it is -
easy to operate
quick in response
effectively handling operational errors
providing simple and consistent user interface
1.c.Software requirements
A System Requirements Specification (SRS) (also known as a Software
Requirements Specification) is a document or set of documentation
•Business Drivers
•Business Model
•Technical Requirements
•System Qualities
•Constraints and Assumptions
1.d.Software requirements document
A document or set of documentation
2.Requirement Engineering
Requirement Engineering Process
•Feasibility Study
•Requirement Gathering
•Software Requirement Specification
•Software Requirement Validation
2.a.Feasibility study
Requirements are categorized logically as
Must Have
Should have
Could have
Wish list
2.b.Requirement Elicitation Process
Requirement Elicitation Techniques
There are various ways to discover requirements
Interviews
several types of interviews such as:
•Structured (closed) interviews
•Non-structured (open) interviews
•Oral interviews
•Written interviews
•One-to-one interviews
•Group interviews
Surveys
Questionnaires
Task analysis
Domain Analysis
Brainstorming
Requirement Engineering
Process
2.c.Software Requirement Validation
•Requirements can be checked against following conditions -
If they can be practically implemented
If they are valid and as per functionality and domain of software
If they are complete
If they can be demonstrated
3.Classical Analysis
3.a.Structured analysis
•The analyst to understand the system.
•Analyze and refine the objectives of an existing system and
develop a new system specification
Structured Analysis Tools
During Structured Analysis, various tools and
techniques are used for system development. They
are −
•Data Flow Diagrams
•Data Dictionary
•Decision Trees
•Decision Tables
•Structured English
•Pseudo code
USE CASE
Diagram
DFD
EXAMPLE
Types of DFD
DFDs are of two types: Physical DFD and Logical DFD. The following table lists the
points that differentiate a physical DFD from a logical DFD.
Physical DFD Logical DFD
It is implementation It is implementation
dependent. It shows which independent. It focuses only
functions are performed. on the flow of data between
processes.
It provides low level details of It explains events of systems
hardware, software, files, and and data required by each
people. event.
It depicts how the current It shows how business
system operates and how a operates; not how the system
system will be implemented. can be implemented.
Context Diagram
.
Data Dictionary
Sr.No. Data Name Description No. of
Characters
1 ISBN ISBN Number 10
2 TITLE title 60
3 SUB Book Subjects 80
4 ANAME Author Name 15
Decision Trees
Decision Tables
describing the complex logical
Components of a Decision Table
Condition Stub
Action Stub
Condition Entry
Action Entry
CONDITIONS Rule 1 Rule 2 Rule 3 Rule 4
Advance Y N N N
payment made
Purchase - Y Y N
amount = Rs
10,000/-
Regular - Y N -
Customer
ACTIONS
Give 5% discount X X - -
Give no discount - - X X
Structured English
if customer pays advance then Give 5% Discount
else if purchase amount >=10,000
then if the customer is a regular customer
then Give 5% Discount
else No Discount
end if
else No Discount
end if
end if
Pseudocode
•Plain English.
•It is used in conjunction with structured
programming.
•It replaces the flowcharts of a program.
End of UNIT -2
