Software Requirements Till User Stories.pdf

Requirements : Why Important?
The requirements
specification was
defined like this
The developers
understood it in
that way
This is how the
problem was
solved before.
This is how the
problem is
solved now
That is the program after
debugging
This is how the program is
described by marketing
department
This, in fact, is what the
customer wanted …

Software Lifecycle
•A sample Software Life cycle Concept Exploration- area where one would like to
position the product
Requirements, Design and Construction part of the
standard development phase
Testing, installation and Check out the part of the
system validation process
Operation and maintenance involves mass deploying
the product at customer sites and handling customer
issues and entering the maintenance process
Retirement- phasing out the product and introducing
the newer one in its place

What are Requirements?
Can we convert physical
records to computerised form?

•Example scenario
To automate records of student in university that were maintained manually.
To support the business processes of the organisation.
To control the process of floor cleaning using robo.
To gather the agriculture data of various states and suitably suggest the manure,
fertilizers and pesticides of wide variety of crops
etc.
“Requirements define what the system must do and how well the system must perform
within identified constraints”

• Specify the functionality of software
• Establish the interfaces external to the software item.
• Provide performance specifications
• Set forth the qualification criteria for software testing.
• Set forth the human factors engineering specifications for the user
interface.

Requirements Specify “What” not “How” !
•What and How- Sometimes the requirements analyst may get lost
into realising the functionality and specify the design approach for a
requirement instead of really documenting what the software shall do
• What the software shall do should be documented in detail during the
requirement phase.
• The How should be the topic of focus during the design phase.

Requirements specify “What” and not
“How”!
•In a student record management system , consider the feature of
entering enrollment number to display the result of a student
•Requirement that specifies “how ” (not recommended) : “If the user
inputs the enrollment number out of range of the system shall flash
an error message in red for 10 seconds ”

Software Requirements: Why Care?
•Rework is the major consequence of requirements problems
-Rework can consume 30% to 50% of total development costs
-Requirements errors can account for 70% to 85% of the rework cost
•Cost of fixing requirements problems at later stages can be high
-Assume that it costs $1 to fix a requirements defect when still
working on requirements; the cost to fix that defect during
operation can be $100 or more on a relative scale

•Shortcoming in requirements practices can pose manyrisks to project
success
-Where success means delivering a product that satisfies the user's
functional and quality expectations at the agreed upon cost and
schedule
•Following sound requirements practices help create high quality
products with faster development and delivery times with less effort
spent in rework

Cost
to
change
Stage
Requirements Design Construction Test Maintenance

•"The hardest single part of
building a system is deciding
precisely what to build. No other
part of the conceptual work is as
difficult as establishing the
detailed technical requirements,
including all interfaces to the
people, to machines, and to
other software systems. No
other part of the work so
cripples the resulting system if
done wrong. No other part is
more difficult to rectify later
- Frederick P. Brooks Jr

Software Requirements Knowledge Area
(KA)
Software
Requirements
Requirements
Developments
Requirements
Management
Requirements
elicitation
Requirements
analysis
Requirements
specification
Requirements
validation

Discussion Question
Consider the following requirement: "The system shall have 3-tiers: a
web-based presentation tier, logic tier, and data tier that uses a
relational database." ?
Is this an acceptable requirement?

Discussion Question
Consider the following requirement: “The system shall have 3-tiers: a
web-based presentation tier, logic tier, and data tier that uses a relational
database.” Is this an acceptable requirement?
ANSWER: Requirements should focus on WHAT is required to be solved by
the system and not the HOW part: specifying that the system should consist
of 3-tiers is about HOW aspects of the system.
Since the requirement talks about the HOW part, this is not an acceptable
requirement.

Functional vs. Non-Functional Requirements
Functional requirements Non-Functional Requirements
(NFRs)
• Describe the functions that
the software is to execute
• Also known as "capabilities"
or "features"
• Non-functional requirements
are the ones that act to
constrain the solution .
• Also known as "constraints”
or “quality
requirements”

Functional vs. Non-Functional Requirements
Business
objectives
Features Qualities
Robustness
Functional
Requirements
Usability Performance etc.
Reliability
Non- Functional Requirements

Exercise: Understanding NFRs
Non-Functional Requirement Name Description
A. Reusability 1.How well the system uses the processor
capacity
space, communication, or band width
B. Efficiency 2. How easy it is to correct a defect or make a
change to the software
C. Testability 3. Extent to which a component designed for one
application can be used in an totally different
application
D. Portability 4. The ease with which the software components
or integrated products can be tested
E. Maintainability 5. Effort required to move or migrate software
from one OS to an other
F. Usability 6. Degree to which the system continues to
function correctly when confronted with invalid
data
G. Robustness 7. Ease to use and human engineering, user

Exercise: Understanding NFRs
Non-Functional Requirement Name Description
A. Reusability 3. Extent to which a component designed for one
application can be used in an totally different
application
B. Efficiency 1. How well the system uses the processor
capacity, disk space, communication, or band
width
C. Testability 4. The ease with which the software components
or integrated products can be tested
D. Portability 5. Effort required to move or migrate software
from one OS to an other
E. Maintainability 2. How easy it is to correct a defect or make a
change to the software
F. Usability 7. Ease to use and human engineering, user
friendliness
G. Robustness 6. Degree to which the system continues to
function correctly when confronted with invalid

Desirable properties of Set of Requirements
Realistic
Complete
Correct
Modifiable
Ranked for
Importance
or Stability
Set of
Requirements

Desirable Properties of Individual
Requirements
cl
Individual
Requirements
Clear
Quantifiable
Prioritized
Verifiable
Traceable Feasible
Unambiguous
Consistent
Concise

Functional Requirements: Examples
•In airline tracking system, the system shall assign a unique PNR
number to each booking.
•FastTag in electronic Toll collection system assign UPI Id for making
toll payments from customers linked prepaid or saving account.

Non Functional Requirements: Examples
•In Airline Tracking System
“Given a PNR number as input, the system should display the status of
the flight within 3 seconds to the user (performance requirement).
“The System shall protect against unauthorised addition or deletion of
PNR number.” (Security Requirement)

Some Common NFRs… (1)
Availability Planned uptime, actually available and fully
operational. Example : The system should be
available 99.999% of the time.
Efficiency How well the system uses the processor capacity, disk
space , communication bandwidth etc.
Flexibility How much effort is needed to add new capability to
the product.
Interoperability Exchange data or services with other systems.
Reliability Software executing without failure
Robustness Degree to which the system continues to function,
correctly when confronted with invalid data; also
ability to recover from failures

Some Common NFRs…(2)
Usability Ease of use and human engineering, user friendliness
Maintainability How easy it is to correct a defect or make a change to the software
Portability Effort required to move or mitigate software from one platform to another.
Example: The system should support the following operating systems:
Windows 8.0 and above and Mac OS 8.0 and above.
Reusability Extent to which a component designed for one application can be used in
an totally different application
Testability Ease with which the software components or integrated products can be
tested.

Exercise: Classifying Requirements
•FRs : “Functional Requirements” (also called capabilities), state what
the software must perform.
• NFRs : “Non Functional Requirements” specify the criteria that can be
used to judge the operation of the system.
•Exercise is to match the requirements in the left-hand-side column
with the CLOSEST requirement kind given in the right-hand-side
column.

Exercise: Classifying Requirements
Requirement Functional Requirement (FR) /
Non-Functional Requirement(NFR)
A. The system should display the result of the student within 1
second.
Select one of : [FR/ NFR]
B. The date of birth of the student should be displayed in
DD/MM/YYYY format
C. The student portal should support 10,000 students of the
university at a given point of time.
D. The university website should be available 99.999 % of the time. Select one of : [FR/ NFR]
E. The student must be able to download the syllabus of the semester
as PDF (Portable Document Format) Files.
F. The system should be menu-driven. Select one of : [FR/ NFR]
G. 80% of the new students registration must be able to take the
details in the database within the first 5 minutes of time.

Desirable Properties of Requirements
Clear Requirements should be written in precise simple language that every reader
can understand. Example: How easy is it for a customer to use the system?
Concise Requirements should describe a single property and expressed with as few words
as possible. For Example: in the library automation problem, you should not
specify whether the library membership records need to be stored sorted on the
member’s first name in a descending order arrangement.
Consistent No requirement should contradict another. For example: one of the clerks
described that a student securing fail grades in three or more subjects should
have to repeat the entire semester. Another clerk mentioned that there is no
provision for any student to repeat a semester.
Unambiguous A requirement should have only one interpretation. For example: In a process
control application , a requirement expressed by one user is that when the
temperature becomes high , the heater should be switched off. Words such as
high, low, good, bad etc. are ambiguous without proper quantification.
Feasible A requirement should be realizable with a specified time frame. Example: It is the
probability and percentage of the software performing without failure for a

Desirable Properties of Requirements
Realistic The goals that are represented by the requirements should be attainable within
time, resource and cost constraints placed upon the project. Example : Each page
must load within 2 seconds. The process must finish within 3 hours so data is
available by 8 a.m. local time after an overnight update.
Complete All the services needed from the system should be included. For example: In a
chemical plant automation software, one of the requirements is that if the internal
temperature exceeds 200 degree C then the alarm bell must be sounded. However
there is no provision for resetting the alarm bell in any of the requirements.
Correct An SRS is correct if and only if every requirement stated therein is one that the
software shall meet.
Modifiable Changes to the requirements should be able to be made easily, completely and
consistently while retaining the structure and style. Example: Customers frequently
change the requirements during the software development development due to a
variety of reasons. Therefore, in practice the SRS document undergoes several
revisions during software development. Also, an SRS document is often modified
after the project completes to accommodate

Example: Verifiable Requirements
The functional :
"The white
requirement board
printer should
support printing
A2 size sheets"
-verifiable as an
individual feature
The non-functional
requirement
(NFR): "The
whiteboard printer
should complete
booting in 2
seconds":
verifiable at
system level

Emergent Properties
•Some requirements represent emergent properties of software
that is, requirements that cannot be addressed by a single
component but that depend on how all the software components
interoperate
-Example: The throughput requirement for a call centre would, for
example, depend on how the telephone system, information system, and
the operators all interacted under actual operating condition.
•Emergent properties are crucially dependent on the system
architecture

Quantifiable Requirements: Example
Ambiguous (un-quantified)
requirement
Unambiguous (quantified)
requirement
The call center software should
have higher throughput than the
earlier version of the software
The call center's software must
increase the center's throughput by
20% when compared to the version
10.1 of the software
The software shall be reliable The software shall have a
probability of generating a fatal
error during any hour of operation
of less than 1 * 10-8

Quantifying Requirements
Requirement Type Examples of Measures
Look and feel Rate of acceptance from users
Usability Error rates from the users
Performance and speed Response time from the software
Reliability Downtime of the software
Portability Number of platforms supported
Robustness % of fatal/nonfatal errors
Maintainability Time and work required to make a change inthe
software
Certification Compliance with standards

System vs. Software Requirements
System requirements focus on
the system as a whole
Software requirements are
those requirements that are
derived from system
requirements
Requirements may be allocated
to hardware, software,
organizational processes or
other components of the system
These requirements are
allocated to the software - What
do we want the software in the
system to do?

System vs. Software Requirements
Software
Requirements
System
Requirements
Focus on the system as a whole ("What do you want
the system to do?")
Derived from system requirements ("What
do we want the software in the system to
do?")

Deriving Requirements
Customer Statement/
Voice of the Customer
Business Use Case
System
Requirements
Software
Requirements
Specific Use Case

Discussion Question
Why are the attributes in the
table classified as important
from the user and developer
point of view? Discuss with
examples.
Important primarily
to users
Important to
developers
1. Availability 1. Maintainability
2. Efficiency 2. Portability
3. Reliability. 3. Reusability
4. Usability 4. Testability

Product vs. Process Requirements
Product requirements Process requirements
• What the software must do
or what users must be able
to do with it
• Constraints on development
of the software (including
specification of a
development language or
toolset, verification
techniques, or the overall
process to be followed)

Product Requirements: Examples
•For a course registration system in a university: "The software should
verify that a student meets all prerequisites before he or she registers
for a course“
•For a telecommunications billing application:
-“The software should be able to generate 100 bills per second (performance
requirement)”
-“The software must support Mac OS X and Windows 8.1 and later versions
(portability requirement)”

Process Requirements: Examples
•For a software embedded in a router device: “The software must be
implemented in C language (example of a language constrain)”
For a Networking Management System (NMS) software: “The
software must be implemented using Rational Unified Process (RUP)
method (example of a process constraint)”

Requirements Process Model
• The requirements process takes a business or engineeringproblem
and, from it, creates the specifications for asystem that will provide a
solution to that problem
•This generic process model shows four sets of activities to produce
specifications from business or engineering problem
- Requirements elicitation
- Requirements analysis
- Requirements specification
- Requirements validation

Requirements Process Model
Elicitation Analysis Specification Validation
clarity Close gaps rewrite
Re – evaluate
Confirm ad correct

Requirements Process Activities
Requirements Process Activity Short Description
Requirements elicitation The process of gathering or discovering the
requirements
Requirements analysis The process of reviewing the requirements,
understanding requirements them as individual
requirements and in the larger context of all
requirements, and synthesizing them to specify a
solution
Requirements specifications The creation of the software and system
specificationdocuments
Requirements Validation The set of formal and informal reviews and other
techniques that help ensure that the requirements
will produce a product that will meet the customer’s
needs when operated in its intended environment

Process Actors / Stakeholders
Users
Customers
Market Analysts
Regulator
Software
Engineers
Testing Team
Requirements
engineer/software
engineer

Process Stakeholders
•Stakeholders are people who have an interest in the software
engineering project/product
•It is important to identify stakeholders early in the process
- This will help us ensure that all sources of requirements are included
•It will not be possible to perfectly satisfy the requirementsof every
stakeholder
- It is the software engineer's job to negotiate tradeoffs that are both
acceptable to the principal stakeholders and within budgetary, technical,
regulatory, and other constraints

Typical Process Stakeholders
Role Use of Requirements
Project leader • Determine scope and create project plan
• Get agreement from owners
• Track progress
Analyst • Elicit requirements
• Decompose requirements
Development team • Design and code to requirements
Engineer efficiency and reuse
Test team • Verify conformance to requirements
Project Sponsor • Provide motivation and sign off
Maintenance team • Support users in production.
• Ensure changes fit requirements

Review Question
You are a requirements analyst working on gathering or discovering the
requirements by interviewing various project stakeholders. Which
requirements process activity are you performing?
a) Requirements elicitation
b) Requirements analysis
c) Requirements specification
d) Requirements validation

Requirements Elicitation
•Requirements elicitation is the process of working proactively with all
stakeholders gathering their needs, articulating their problem,
identify and negotiate potential conflicts thereby establishing a clear
scope and boundary for a project
•It can also be described as a process of ensuring that the stakeholders
have been identified and they have been given an opportunity to
explain their problem and needs. And describe what they would like
the new system to do

Dimensions of Requirements Elicitation
Requirements
elicitation:
Dimension
Understanding the problem
Understanding the domain
Identifying clear business objectives
Understanding the needs
Understanding constraints of the system
stakeholders
Writing business objectives for the project

Requirement Sources
High Level Goals
Feasibility
study
Focus
Groups
Stakeholders and System Context
Organizational
Environment
Operational
Environment
Requirements Elicitation
Understanding
problem
Write Business
Objectives
Gather
Information
from
Stakeholders

Goals
•The "goal" (sometimes called "business concern" or "critical success
factor") refers to the overall, high-level objectives of the software
• Goals provide the motivation for the software but are often vaguely
formulated.
•A "feasibility study" is a relatively low-cost way to assess the viability
or practicality of realizing the goals

Interviews
•Interviewing stakeholders is a "traditional" means of eliciting
requirements
Advantages Disadvantages
• Effective to get an overall
understanding of what
stakeholders do and how
they are likely to interact
with the system
• Stakeholders language is
so filled with
business-related jargon
hard for engineers to
understand
Stakeholders find some
key activities so familiar

Prototypes
•Prototyping technique is a valuable
tool for clarifying ambiguous
requirements.
•Wide range of prototyping
techniques available ranging from
paper mockups of screen designs to
beta-test versions of software
products
GUI Builder
GUI

Facilitated Meetings
•Stakeholders brainstorm and refine ideas in a meeting facilitated by a
moderator
Advantages Disadvantages
• Bring more insight into their
software requirements than
by working individually.
• Conflicting requirements
surface early
• Result in a richer and more
consistentset of
requirements
• Critical abilities of the team
may get eroded by group
loyalty
• Concerns of a few
outspoken (and perhaps
senior) people may get
favoured to the detriment of
others

Observation
•When using observation technique,
software engineers learn about user
tasks by immersing themselves in
the environment and observing how
users perform their tasks by
interacting with each other and with
software tools and other resources.

User Stories
•Refers to short, high-level descriptions of required functionality
expressed in customer terms
A user story is intended to contain just enough inform so that the
developers can produce a reasonable esti of the effort to implement it
User stories is a commonly used technique in Agile Methods
computer society

User Stories: Template
Template
“As a <role>, I want <goal/desire> so that <benefit>”
Example
“As a buyer,
I want the check out page to have “confirm” button so
that I can review the order before paying the money”

Software Requirements Till User Stories.pdf

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