Software Requirements and Specifications

Virtual University Help Forum
CS510: Software Requirements and Specifications
WEEK 01, SLIDE 01:
Why this course needed?
◦ Let’s visualize how it is difficult to understand others point of view
Course learning objectives
◦ To understand the role of Software Requirement and Specification (SRS) in software
projects.
◦ To understand the essential nature of SRS.
◦ To study current techniques, notations, methods, processes and tools used in SRS.
◦ To gain practical experience in writing of the SRS document
Course Evaluation
◦ Assignments
◦ Discussion/Presentation
◦ Quizzes
◦ Midterm exam and
◦ Final term exam
Course Textbooks
◦ Requirements Engineering: Processes and Techniques, Gerald Kotonya and Sommerville,
John-Wiley Sons, 1998 (or Latest Edition).
◦ Software Requirements, Karl E. Wiegers, Microsoft Press, 2003(or Latest Edition).
◦ Software Requirements Specification, David Tuffley, CreateSpace Independent
Publishing Platform, 2010 (or Latest Edition).
◦ System Requirements Engineering, Loucopoulos and Karakostas, McGraw-Hill, 1995 (or
Latest Edition).
Topics to be covered
◦ Software Requirement basic concepts. (What, Why and Who)

◦ SRS processes: Sequence of activities that need to be performed in the requirement
phase
◦ Requirement Elicitation: Process of discovering, reviewing, documenting, and
understanding the user's needs and constraints for the system.
◦ Requirement Modelling: Visualization of requirements for better understanding and
analysis
◦ Requirement Analysis: Refining the user's needs and constraints
◦ Requirement Specification: Process of documenting the user's needs and constraints
clearly and precisely.
◦ Requirement verification and validation: Process of ensuring that the system
requirements are complete, correct, consistent, and clear.
◦ Requirement Management: Scheduling, coordinating, and documenting the
requirements engineering activities
◦ Requirement Traceability: if the source of the requirements can be identified
WEEK 01, SLIDE 02:
Introduction
 What is a Requirement?
◦ Something required, something wanted or needed
◦ A statement of a system service or constraint
◦ A condition or capability that must be possessed by a system (IEEE)
 Why requirement is needed?
◦ Requirements form the basis for all software products
Requirement Challenges
 Challenges
◦ Necessarily involves people interaction
◦ Cannot be automated
 Why it is hard to Understand Requirements?

◦ Visualizing a future system is difficult
◦ Capability of the future system not clear, hence needs not clear
◦ Requirements change with time
Requirement Task
 Input
◦ Users need in mind of people
 Output
◦ precise statement of what the future system will do
Requirement Examples
◦ The system shall allow users to search for an item by title, author, or by International
Standard Book Number
◦ The system’s user interface shall be implemented using a web browser
WEEK 01, SLIDE 03:
Requirement Engineering (RE)
 What is a Requirement Engineering?
◦ Requirement Engineering is a new area which is started in 1993.
◦ The first International symposium was held On RE in 1993.
◦ It is the process, which is used to determine the requirements for a software product
systematically.
 What is a Requirement Engineering?
◦ The development and use of technology effective to elicit, specify and analyse
requirements from stakeholders (clients/users) that shall be performed by a software
system
Importance of RE
◦ “26% of the Software projects were considered a success.”
◦ Meaning that 74% have FAILED!

Standish Group, CHAOS Report,
2000
◦ “56% of the errors in a software can be traced back to the requirements phase”
Tom De Marco (a US Software
Engineer)
◦ The hardest part of building a software 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 of the interfaces to 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
Fred Brooks
◦ Software complexities
◦ Frequent change in user requirements
◦ Outsourcing offshore projects
◦ Cost of fixing errors
◦ Causes of failure
WEEK 02, SLIDE 01:
Characteristics of Good Requirements
 How to judge good and bad requirements?
◦ There are several criteria need to meet for good requirements.
◦ Usually overlooked in requirement process
◦ An excellent source to measure projects quality and progress.
◦ Characteristics of requirements vs Characteristics of Requirement Specification.
◦ Meaning become somehow different when considering a single requirement or a set of
requirements i.e. SRS
Key characteristics of good requirements

1. Feasible
2. Valid
3. Unambiguous
4. Verifiable
5. Modifiable
6. Consistent
7. Complete and
8. Traceable
1- Requirement Feasibility
 Also considered as Realistic or possible
◦ Requirement is feasible if it is implementable within the given constraints or resources
like budget, time and available technology etc.
 Example:
◦ Requirements to handle 10000 transactions/second might be feasible in given current
technologies but might not be feasible with agreed platform or technology.
2- Requirement Validity
 Normally termed as correct
 Requirement should be valid if and only if the requirement is one that system shall
meet.
 Validity can be done by reviewing with key stakeholders who decide the success or
failure of project
 “must” and “nice to have” requirements should clearly be demarcated
 Example
◦ Car rental prices shall show all applicable taxes (including 6% state tax).
◦ Here mentioning 6% tax is incorrect because it is dependent
References
◦ Software & Systems Requirements Engineering - In Practice Mar 2009

◦ IBM press
WEEK 02, SLIDE 02:
3- Unambiguous Requirements
◦ If a requirement has only one interpretation then it is called unambiguous requirements
◦ Source of ambiguity is:
◦ Natural language
◦ Ambiguity level shows the quality of requirements
◦ Can effect project schedule and budget
Example:
◦ Ambiguous statement:
◦ “The data complex shall withstand a catastrophe (fire, flood).”
◦ Unambiguous statement:
◦ The data complex shall be capable of withstanding a severe fire. It shall also be capable
of withstanding a flood
4- Verifiable requirements
◦ Also termed as testable requirements
◦ Requirements are verifiable if the developed system or application can be tested to
ensure that it meets the requirements.
◦ But product features are not easy to be verified
◦ Proper analysis is needed to make it testable
Example:
◦ The car shall have power brakes.
◦ Abstract so Not testable
◦ Detailed testable requirement:
◦ The car shall come to a full stop from 60 miles per hour within 5 seconds.
5- Requirements Modifiability

◦ Requirements are modifiable if any changes can be made to the requirements easily,
consistently and completely without any changes to the existing structure and style of
document.
◦ Redundancy is a key factor
References
◦ IBM press
WEEK 02, SLIDE 03:
6- Consistent Requirements
◦ A relationship among two or more requirements
◦ A requirement is consistent if it does not contradicts or in conflicts with other
requirements
◦ These requirements should either be external documents, standards or other
requirements.
Example:
◦ Dates shall be displayed in the mm/dd/yyyy format.
◦ Dates shall be displayed in the dd/mm/yyyy format.
◦ Both internal and external consistency is requrired
7- Complete Requirements
◦ A requirement should be present for all conditions that can occur.
◦ Very difficult to Check
◦ Can effect project schedule and budget
◦ There is no way to be sure that all requirements has been captured
◦ Its because user can add new requirements at the end of the requirement engineering
phase.
8- Traceable requirements
◦ Requirements are traceable if the source of the requirements can be identified

◦ It is the ability to describe and follow the life of requirements in forward and backward
direction
◦ Why tractability:
◦ Needed for requirement management and project tracking
◦ If requirements are atomic and having unique id then it would be traceable.
References
◦ IBM press
WEEK 03, SLIDE 01:
Kinds of Software Requirements
1- Functional requirements
2- Non-functional requirements
3- Domain requirements
4- Inverse requirements
5- Design and implementation constraints
1- Functional Requirements
◦ Statements describing what the system does
◦ Functionality of the system
◦ Functional requirements should be complete and consistent
 Example
◦ The user shall be able to search either the entire database of patients or select a subset
from it (admitted patients, or patients with asthma, etc.)
2- Non-functional Requirements (NFR)
What are Non-functional Requirements?
◦ Quality factors, design criteria and metrics.
◦ Non-functional requirements define how the system supposed to be.
◦ Most non-functional requirements relate to the system as a whole.

◦ They include constraints on timing, performance, reliability, security, maintainability,
accuracy, the development process, standards, etc
◦ Often more critical than individual functional requirements
3- Domain Requirements
◦ Requirements that come from the application domain and reflect fundamental
characteristics of that application domain
◦ These can be both the functional or non-functional requirements
◦ Example
◦ Most banks do not allow over-draw on most accounts, however, most banks allow some
accounts to be over-drawn
4- Inverse Requirements
◦ They explain what the system shall not do.
◦ Many people find it convenient to describe their needs in this manner
 Example
◦ The system shall not use red color in the user interface, whenever it is asking for inputs
from the end-user
5- Design and implementation constraints
◦ They are development guidelines within which the designer must work
◦ These requirements can seriously limit design and implementation options
 Example
◦ The system shall be developed using the Microsoft Dot Net platform
◦ The system shall be developed using open source tools and shall run on Linux operating
system
References
◦ Software Requirements: Objects, Functions, and States by A. Davis, PH, 1993
◦ Software Engineering 6th Edition, by I. Sommerville, 2000
WEEK 03, SLIDE 02:

Requirement Engineering (RE) Process
 What is process?
◦ A process is an organized set of activities, which transforms inputs to outputs
◦ Processes document the steps in solving a certain problem
 Why process?
◦ They allow knowledge to be reused
◦ Processes are essential for dealing with complexity in real world
 Example
◦ An instruction manual for operating a microwave oven
◦ An instruction manual for assembling a computer or its parts
Software Processes
◦ Software engineering, as a discipline, has many processes
◦ These processes help in performing different software engineering activities in an
organized manner
◦ Examples
◦ Software engineering development process (SDLC)
◦ Requirements engineering process
◦ Design process
◦ Quality assurance process
References
◦ Requirements Engineering: Processes and Techniques’ by G. Kotonya and I.
Sommerville, John Wiley & Sons, 1998
WEEK 03, SLIDE 03:
Requirement Engineering (RE) Process
 What is RE process?

◦ The process(es) involved in developing the system requirements collectively called RE
process(es)
 Which process to be used?
depends on:
◦ application domain
◦ the people involved and
◦ the organisation developing the requirements.
◦ Generic activities which is common to all processes
◦ Requirements elicitation
◦ Requirements analysis
◦ Requirements validation
◦ Requirements management.
Input and Output to RE Processes
RE activities (Linear Model)

RE activities (Spiral Model)
References
◦ Requirements Engineering: Processes and Techniques’ by G. Kotonya and I.

◦ Requirements Engineering Processes, Tools/Technologies & Methodologies S. Arif et al.
WEEK 04, SLIDE 01:
Requirements Elicitation Techniques
• Requirements Elicitation
• Purpose of Requirements Elicitation
• Basic Requirements to use
• Types of Requirements Elicitation Techniques
• Capability of Requirements Elicitation Technique
• Pros and Cons of different elicitation techniques
Requirements Elicitation
• Requirements Elicitation (RE) is defined as the process of obtaining a comprehensive
understanding of stakeholder’s requirements
• RE is the initial and main process of requirements engineering phase.
• RE is a complex process
• Criteria for obtaining High quality requirements
Requirements Elicitation methods Overview
• Interviews, Questionnaires, Observation, Joint Application Development (JAD), Brainstorming
etc
• Which one is best?
• RE is considered an incomplete process in Requirement Engineering.
• Applying inappropriate techniques
Requirements Elicitation techniques
• Procedures to obtain user requirements, implement in the system to fulfill user’s requirements.
• Selection of appropriate elicitation technique
• Factor ( Business procedures, resources available, project type, individual preference etc )

• Characteristics of RE technique
• Type of Application
Classification of different requirements elicitation techniques
• 1) Traditional Technique
Interviews, Questionnaires/Surveys, and Document analysis.
• 2) Contextual Techniques
Observation, Ethnography and Protocol Analysis.
• 3) Collaborative/Group Techniques
Prototyping, Joint Application Development, Brainstorming, and Group Work
4) Cognitive Techniques
Laddering, Card Sorting, Repertory Grids and Class Responsibility Collaboration
Interviews
Basic concepts
◦ verbal method , easy and effective, most employed
Types of Interviews: Structured or Closed Interviews:
General characteristics
◦ predefined questions ,
◦ quantitative data,
◦ No generation of new idea,
Pros:
• No biasing ,Few additional questions may be added to further add clarification, Interview can be
repeated
Cons:
• interviewee may be uncomfortable ,
Semi-structured Interviews:

• combination of predefined and unplanned questions.
Pros:
• Consistency,
• interviewee can share new ideas
Cons:
• Time consuming, interviewer may lose its focus ,Training required,
• Findings are hard to generalize
Unstructured or Open Interviews
• informal interview containing unplanned questions, Producing qualitative data
Pros:
• New ideas and opinions are generated.
• Due to informal approach interviewer may feel ease to properly answer questions.
Cons:
• Interviewer can be biased in asking questions.
• Difficult to repeat in case data reliability is checked.
Summary: Interviews
• Advantages: Good for complex topic, Rich in information, Ambiguities are clarified. Interviewer
can analyze emotions .Non-responsiveness remains low. Provides overview of the whole
system.
• Disadvantages: Small number of people involved, Information cannot be gathered from large
population, Quality of data gathered depends on the skills of interviewer,
Document Analysis
• Analyzing and gathering information from existing documents
• Effective to initiate requirements elicitation process
• Why use this technique?
• An expert needs to study domain information thoroughly for the purpose of adapting when
existing system needs to be replaced or enhanced.

• Design documents, templates and manuals of existing systems.
Pros:
• · Helpful when stakeholders and users are not available.
• · Helps business analyst to get proper understanding of the organization before meeting the
stakeholders there.
• · Provides useful historical data.
• · Can be useful to frame questions for interviews.
• · Can be used for requirements reuse.
• · Inexpensive technique.
Cons:
• · Time consuming to find information from huge amount of documentations.
• · Sometimes valid information may not be available i.e. documents may be outdated.
• · Periodic updating of documents is required.
• · Information might be incomplete.
Questionnaires/Surveys
• cheapest way of eliciting requirements
• When to use this technique?
• No face to face
• collect requirements from a larger group of population distributed over a large geographical
area and from different time zones
• Questionnaires must be clear, well-defined and precise besides including the domain knowledge
Pros:
• · Reach large number of people within a short time.
• · Useful when same question is asked to large number of people.
• · No biasing occurs.
• · It is economical.

• · Easy because multiple choice questions or true false or fill in the blanks are included.
Cons:
• · Cannot get further clarification regarding the problem what analyst actually wants from the
user.
• · Questions can be misinterpreted.
• · Sometimes useful feedback isn’t received.
• · To get further information other techniques like interviews can be used as follow ups.
• · Sometimes question ambiguities may arise.
• · Used for general purpose software.
Introspection
• Analysts work for what they imagine and observe by themselves how a system design should be.
• This technique is effective with users who have a lot of experience of their own fields but have
less knowledge about the other fields as well as the new system.
Pros:
• · There are almost no costs for implementing this technique.
• · Easy to implement.
• · It can act as a good initial step to start requirements elicitation.
Cons:
• · It is hard for analysts to imagine the environment in which the new system works.
• · It doesn’t allow discussion with stakeholders and other experts. Therefore, it is not encouraged
if not used in combination with other techniques.
• · Analysts and stakeholders need to be well known about the domain.
WEEK 05, SLIDE 01:
Contextual Techniques
• Techniques in this category are Observation, Ethnography and Protocol Analysis.
Observation/Social Analysis:
• The requirements engineer observes the user’s environment without interfering in their work.

• This technique is used when customer is not able to explain what they want to see in the
system, how they work and when some ongoing processes are to be monitored.
• Combination with other requirements elicitation techniques like interviews.
• Passive observation
• Active observation
Observation
Pros:
• Authentic and reliable because analysts by himself goes to observe the environment.
• Can be useful to confirm and validate requirements collected through other methods.
• It is inexpensive method.
• Gives idea about how users will interact with the system.
• Helpful in work measurements i.e. how long particular task takes to be done
Cons:
• All the requirements cannot be checked in just a single session; multiple sessions may be
required.
• Users can behave indifferently while they are interrupted for asking questions in active
observation.
• In passive observation, it is difficult for analyst to make out why some decisions are made.
• It is time consuming
Ethnography
• Study to understand Relationships between actors, workplace
• Used in combination with other elicitation techniques like interviews and questionnaires
Pros:
• Helps to discover certain features of a work place in a shorter time period.
• Helps understand how people work in an organization and how they interact with each other.
• Doesn’t need much resource to be effective.
• Helps reveal critical events not observed by any other technique.

• Useful in validating requirements
Cons:
• There is no detailed guide on how to perform ethnographic technique effectively and therefore,
it all depends on the skills of the person performing it, the ethnographer.
• It requires engineers to have a lot of experience to perform it.
• New and unique features added to the system might not be discovered.
• Fails to produce desirable results due to diverse population.
• Focuses mainly on end-users.
• Sometimes it can be time consuming.
• Different backgrounds of users and ethnographers can result in misunderstanding problems
between them.
Collaborative/Group Techniques
• Group elicitation techniques involve teams or groups of stakeholders who applying their
individual expertise on a particular issue agree upon a set of decisions
• Prototyping :
• An iterative process
Pros:
• User involvement during development process.
• Allows early user feedback for requirements refinement.
• Saves development time and cost.
• Users and analysts get better understanding of the system.
Cons:
• The disadvantage is that when users get used to particular kind of system they often resist
changes.
• Effort and cost estimation may get high as calculated earlier.
• For complex systems, it can be time consuming.
Joint Application Development (JAD)

• JAD sessions are basically collaborative workshops that last for 4-5 days and whose outcome is a
proper set of user requirements.
Pros:
• Decreased time and cost of requirements elicitation.
• Accelerates design of the system
• New and rapid idea generation leading to creative outputs.
• Promotes user feedback.
• More user satisfaction.
• Good communication between stakeholders, analysts and other professionals.
• Visual aids and case tools used make the session interactive.
Cons:
• If not properly planned can lead to wastage of time and resources.
• Requires trained facilitators.
• Requires lots of planning and effort.
• It is an expensive technique.
Brainstorming
• It is an informal discussion where free expression of ideas is given to every participant for a new
kind of system to be developed
Pros:
• Costs very little and not much resources are needed.
• Participants need not to be high qualified and each participant takes part actively in the process.
• It is comprehensible and easy to implement.
• Helps in new ideas generation.
• Helps in conflict resolution.
• Each participant is equally allowed to speak and share ideas.
Cons:

• It is not suitable to resolve major issues.
• If not organized properly can be time consuming.
• Quantity of ideas doesn’t always equal their quality.
• Can lead to repetition of ideas if participants are not paying proper attention.
• Some people due to extrovert nature may take over all the session and all the time sharing their
ideas and other people who are less outgoing will be afraid to take the time sharing their views.
Group Work
• In this technique, stakeholders are invited to attend a meeting to elicit requirements for projects
Pros:
• Quality requirements in a shorter period of time.
• Saves cost as compared to conducting interviews of same number of people
Cons:
• It takes lot of effort to bring all the stakeholders on the same table at the same time because of
their busy schedule and political aspects
• Participants may have issues related to trust and may feel hesitate to discuss critical or sensitive
matters.
• Members may get influenced by dominant people in the meeting leading to biased results.
User Scenarios
• Scenarios are representation of user’s interaction with the system. It is a real world example of
how a system is used.
Pros:
• Well-developed scenario helps organizations to be proactive and work specifically for the
desired product.
• Gives good clarifications regarding an activity or event its normal flow, exceptional behavior,
alternative paths.
• People with no technical knowledge can also understand it.
• Easy to understand as no special language is used to write them.

• Ensures system is designed properly as end-user’s perspective is considered for requirements
elicitation.
Cons:
• It is difficult to draw useful scenarios.
• It is not suitable for all types of projects even if they capture more requirements.
• They do not cover all the processes i.e. not the complete view of future system.
Cognitive Techniques
• Laddering
• It is an interviewing technique to elicit stakeholder’s goals, values and attributes.
Pros:
• Easy to understand requirements because of hierarchical nature.
• Reuse of requirements saves time and cost.
• Not good for building a new system.
Cons:
• Maintaining requirements is a difficult task while adding or deleting any user requirement
anywhere in a hierarchy.
• Technique becomes complex when requirements are in large number.
• Expert opinion or initial data is must to elicit requirements.
• It is too long and tiring technique
Card Sorting
• It is a knowledge elicitation technique in which stakeholders are asked to sort cards according to
domain entity names using index cards or some software packages.
Pros:
• It is fast and inexpensive.
• It is accessible through internet so the participants that are geographically remote can take part
in it.
• It is reliable and easy technique.

• Helpful in providing good understructure.
• It is an established technique.
• Useful in gathering qualitative data.
• It involves real inputs from the users.
• Makes information structured to be fed into information process
WEEK 06, SLIDE 01:
Modeling
 A picture is worth 1000 words.
 A model is a representation of reality, like a model car, airplane.
 Most models have both diagrams and textual components.
Why Modeling?
 Visualization.
 Communicate with customer.

 Reduction of complexity.
Requirements modeling
 A requirements model is a set of these diagrams, each of which focuses on a different aspect of
the users' needs.
 A requirements model provides greatest benefit if you use it to focus discussions with the users
or their representatives.
 Each model provides a particular type of information.
Why Requirements modeling?
 Modeling can guide elicitation.
 Modeling can provide a measure of progress.
 Modeling can help to uncover problems.
 Modeling can help us check our understanding.
Usecase diagram
 A use case is a list of actions/tasks.
 Who uses the system and what they do with it.
 Use case diagram can identify the different types of users of a system and the different use
cases

State machine diagram
 One of the challenges faced by requirements analysts is the need to communicate the complex
behavior of systems in an understandable yet rigorous and verifiable way.
 State machine works well for this purpose.
 State machine captures information about states an object can go through during its lifecycle.
Summary
 Modeling.
 Benefits of Modeling.
 Requirements Modeling.
 Benefits of requirements modeling.
 Use case diagram and State machines.
WEEK 06, SLIDE 02:
Use case modeling
 Use case diagrams describe what tasks the system performs.
◦ E.g. Order placement, a ticket reservation, assignment submission etc.
 Who uses the system
◦ A customer, a librarian, a student etc.
 Which user interacts with which use case.
Sample Use case model

Components of use case
 Use case: subset of the overall system functionality.
 Actor: Anyone or anything that needs to interact with the system to exchange information.
 Association: which actor interacts with which use case.
Sample use case diagram
 A Librarian updates a book catalogue
 A Librarian updates a book catalogue

 A passenger buys ticket
Reuse (dependency) in use case
 Extends: An extend dependency, formerly called an Extends relationship is a generalization
relationship where an extending use case continues the behavior of a base use case

 Includes: An include dependency, is a generalization relationship denoting the inclusion of the
behavior described by another use case.
Sample use case diagram
 Ticket Reservation System

Includes vs Extends
 Includes
◦ You have a piece of behavior that is similar across many use cases
◦ Break this out as a separate use-case and let the other ones “include” it.
◦ <<Includes>> keyword is used.
 Extends
◦ A use-case is similar to another one but does a little bit more
◦ Put the normal behavior in one use-case and the exceptional behavior somewhere else.
◦ <<Extends>> keyword is used
Summary
 Use case modeling.
 Components of use cases
 Reusability in use cases.
WEEK 07, SLIDE 01:

Use case modeling (Case Study)
Air Ticket Reservation System
 Reservations on local system
 Passenger goes to client terminal in local office
 Searches flights/seats.
 Takes print of available seats.
 Booking staff confirms seat.
 Client terminal also displays flash news/updates.
 Admin can Add/Edit/Cancel flight schedule (Email is sent to passengers)
 Admin can cancel ticket.
 Admin can Add/Edit/Cancel Reservation
 Actors
 Passenger
 Admin
 ?
 Use cases
 ViewNewsFlash
 PrintSchedule
 SearchSeat
 AddFlight
 ReserveSeat
 EditReservation
 CancelReservation
 Use cases
 SendEmail

 AddFlight
 EditFlight
 CancelFlight
 AddUser
 EditUser
 DeleteUser
Diagram 1:
Diagram 2:
Diagram 3:

Diagram 4:
Diagram 5:

Diagram 6:

Diagram 7:
Diagram 8:
Diagram 9:

Diagram 10:
Diagram 11:

Diagram 12:
Diagram 13:

Diagram 14:
Diagram 15:

Diagram 16:

Diagram 17:
Diagram 18:
Diagram 19:

Diagram 20:
Diagram 21:

WEEK 07, SLIDE 02:
Use case modeling
(Part 2)
Steps in usecase modeling
 Step-1: Identify business actors.
 Step-2: Identify business use cases.
 Step-3: Construct use-case model diagram.
 Step-4: Documents business requirements use-case narratives.

Step-1: Identify business actors.
 Who or what provides inputs to the system?
 Who or what receives outputs from the system?
 Are interfaces required to other systems?
 Who will maintain information in the system?
 Actors should be named with a noun or noun phrase
Step-2: Identify business use cases.
 What are the main tasks of the actor?
 What information does the actor need from the system?
 What information does the actor provide to the system?
 Use cases should be named with a verb phrase specifying the goal of the actor (e.g. PlaceOrder)
Step-3: Construct use-case model diagram.
Step-4: Documents business requirements use-case narratives.

Summary
 Steps of use case modeling
 Documenting usecase narrative
WEEK 08, SLIDE 01:
State machines
Muhammad Summair Raza
Statemachine modeling
 Many information systems deal with business objects that involve a series of possible states.
 Describing a set of complex state changes in natural language creates a high probability of
overlooking a permitted state change or including a disallowed change.
 State machines provide a concise, complete, and unambiguous representation of the states of
an object or system.
 It relates events and objects.
 States - A state is denoted by a round-cornered rectangle with the name of the state written
inside it.

 Initial and Final States - The initial state is denoted by a filled black circle and may be labeled
with a name. The final state is denoted by a circle with a dot inside and may also be labeled with
a name.
 Transition - Transition from one state to the next is denoted by lines with arrowheads.
 Trigger is the cause of the transition.
◦ A signal.
◦ An event.
◦ A change in some condition.
◦ The passage of time.

Nested State Diagram
 State diagrams can be structured to permit concise descriptions of complex systems.
 It allows an activity to be described at a high level, and then expanded at lower level by adding
details.

Aggregation and concurrency
 Aggregation means concurrency
 Overall state of aggregate object is combination of states of sub-objects
 Car
◦ Ignition
◦ Transmission
◦ Accelerator
◦ Brakes
 Sample state of a car
◦ Ignition: ON
◦ Transmission: Neutral
◦ Accelerator: On

◦ Brakes: Off
◦ Sample state of a car
◦ Ignition: ON
◦ Transmission: Reverse
◦ Accelerator: off
◦ Brakes: On
WEEK 08, SLIDE 02:
State machines
 Many information systems deal with business objects that involve a series of possible states.

 Describing a set of complex state changes in natural language creates a high probability of
overlooking a permitted state change or including a disallowed change.
 State machines provide a concise, complete, and unambiguous representation of the states of
an object or system.
 It relates events and objects.
 States - A state is denoted by a round-cornered rectangle with the name of the state written
inside it.
• Initial and Final States - The initial state is denoted by a filled black circle and may be labeled
with a name. The final state is denoted by a circle with a dot inside and may also be labeled with
a name.

• Transition - Transition from one state to the next is denoted by lines with arrowheads.
 Trigger is the cause of the transition.
◦ A signal.
◦ An event.
◦ A change in some condition.
◦ The passage of time.

Summary
 State machine
 State machine modeling
 Components of state machine
 Sample state machine
WEEK 09, SLIDE 01:
Goal Oriented RE
Traditional RE:
 Traditional RE approaches start from the initial requirements statements (“What”).
 It ignores to focus on “Why” which is objective of GORE

 GORE is concerned with acquisition, modeling and analysis of stakeholder purposes (“goals”) in
order to derive functional and non-functional requirements.
Goals:
 A goal is an objective the system under consideration should achieve.
◦ “Accounts should be secure”
◦ Goals can be expressed at different level of abstraction:
◦ High level goals
◦ Sub-goals
 Goals cover different types of concerns: functional and nonfunctional.
Why GORE?
 Requirements Elicitation
 Exploration of design choices
 Requirements completeness
 Requirements traceability
 Requirements negotiation
A simple goal model

Requirement vs. Goal
 A requirement is a particular way of achieving a goal.
 Goals are at a higher level than requirements
 Goals are more stable than corresponding requirements
Summary
 Limitations of traditional RE
 Why GORE?
 Requirements vs. Goals
WEEK 09, SLIDE 02:
NFR framework
Non Functional Requirement (NFR) Framework
 Key concept is the notion of soft goal.

 Soft goals are goals that do not have a clear-cut criterion for their satisfaction; may be partially
satisfied.
 This construct allows representing goals concerning NFRs of the system as well as ill-defined and
high-level objectives of the stakeholders.
Framework Activities
 Capturing NFRs for the domain of interest.
 Decomposing NFRs
 Identifying possible NFR operationalization (design alternatives for meeting NFRs)
 Dealing with ambiguities, tradeoffs, priorities, and interdependencies among NFRs
 Supporting decisions with design rationale.
 Evaluating impact of decisions.
Soft goal Interdependency Graph
1. The main modeling tool that the framework provides is the soft goal interdependency graph
(SIG).
2. The graphs can graphically represent soft goals, soft goal refinements (AND/OR), soft goal
contributions (positive/negative), soft goal operationalization and claims.
Types of Soft goals in NFR framework:
1. NFR soft goals represent non-functional requirements to be considered
2. Operationalizing soft goals model lower-level (design) techniques for satisficing NFR soft goals
3. Claim soft goals allow the analyst to record design rationale for soft goal refinements, soft goal
prioritizations, soft goal contributions, etc.
Soft goals
 Soft goals can be refined using AND or OR refinements with obvious semantics.
 Also, soft goal interdependencies can be captured with positive (“+”) or negative (“–“)
contributions.

Summary
 NFR framework
 Framework activities
 Soft goal Interdependency Graph
WEEK 10, SLIDE 01:
KAOS (Knowledge Acquisition in Automated Specification)
 Methodology for requirements engineering enabling analysts to
• build requirements models
• Derive requirements documents from KAOS models.
KAOS Ontology
• Objects are things of interest in the composite system whose instances may evolve from state to
state. Objects can be entities, relationships, or events.
• Operations are input-output relations over objects. Operation applications define state
transitions.
• An Agent is a kind of object that acts as a processor for operations. Agents are active
components that can be humans, devices, software, etc.
• A Goal in KAOS is prescriptive statement of intent about some system whose satisfaction in
general requires the cooperation of some of the agents forming that system.
o Goals may refer to services (functional goals) or to quality of services (non-functional
goals).
o In KAOS, goals are organized in the usual AND/OR refinement abstraction hierarchies.
o Goal refinement ends when every sub goal is realizable by some individual agent
assigned to it. That means the goal must be expressible in terms of conditions that are
monitor able and controllable by the agent.
KAOS Models
1. Goal model where goals are represented, and assigned to agents
2. Object model which is a UML model that can be derived from formal specifications of goals since
they refer to objects or their properties

3. Operation model which defines various services to be provided by software agents.
4. Responsibility models for various agents
Building the Goal Model
 Good Practices
◦ Requirements Patterns, grown over time as organizational experience with GORE
matures
◦ Milestone driven refinement of goals as a guide for completeness
Example: Generic Goal Pattern

Example: Generic Conflicting Goals
The Elevator Case Study
Problem Statement: You’ve just been hired by an elevator design company to improve performance and
quality of software development within the company. You’ve directly pointed out a major weakness in
the way software is developed there is currently no formal requirements engineering method in use. As
a first challenge, you are asked to build a KAOS model for a new elevator system to be designed.
Instantiating the Generic Goal Model

Goals covered in case study
1. “Transportation requests satisfied” (i.e. functional need)
2. “Safe elevator system” (i.e. non-functional need)
Transportation Request Satisfied: Generic Pattern for Service Requests Satisfaction
A Note on Terminology
 Look at the previous figure and notice the way goals have been named: a word followed by verb
in its passive form. For instance, we have written “Service requested” instead of “Request
service” or “The passenger must request the service”.
 The reason is to avoid confusion between goals and operations (agent behaviors). Goals
basically refer to system states we want to achieve or maintain, cease or avoid. They do not
refer to system state transitions.
Instantiating the Service Request Satisfaction Pattern

Elevator Called: Generic Service Request Pattern
Goal Model Completeness Criteria
 Completeness criterion 1: A goal model is said to be complete with respect to the refinement
relationship ‘if and only if’ every leaf goal is either an expectation, a domain property or a
requirement.
 Completeness criterion 2: A goal model is complete with respect to the responsibility
relationship ‘if and only if’ every requirement is placed under the responsibility of one and only
one agent (either explicitly or implicitly if the requirement refines another one which has been
placed under the responsibility of some agent).
Elevator Called: Instantiating the Pattern

Summary
 KAOS Goal Model
 Terminologies
 Completeness criteria
WEEK 10, SLIDE 02:
KAOS Object Model
 Used to define and document concepts of the application domain that are relevant with respect
to the known requirements and provide static constraints on operational system.
 Objects pertaining to the stakeholders’ domain
 Other objects introduced on purpose to express requirements or constraints on the operational
system.
Types of Objects
 Entities:
◦ Represent independent, passive objects.
◦ For instance, elevator doors, buttons, etc...
◦ ‘Independent’ means that their descriptions needn’t refer to other objects of the model.
◦ They are ‘passive’ means they can’t perform operations.
 Agents:
◦ Represent independent, active objects.
◦ For instance, Elevator Company, passenger, elevator controller etc.
◦ They are active meaning they can perform operations.
◦ Operations usually imply state transitions on entities (for instance, the “Ring Alarm”
operation implies the following state transition on the entity “Alarm”: status attribute
changed from “Silent” to “Ringing”).
 Associations:
◦ Dependent, passive objects.
◦ ‘Dependent’ because their descriptions refer to other objects.

◦ For instance, the “At” association links a Cage to a Floor. An instance of that association
(say between Cage ‘c’ and Floor ‘f’) would hold if cage ‘c’ is currently located on floor ‘f’.
◦ They are passive so they can’t perform operations.

Summary
 KAOS Object Model
 Types of objects
 Example
WEEK 11, SLIDE 01:
KAOS Operational Model
 The KAOS operation model describes all the behaviors that agents need to fulfill their
requirements.
 Behaviors are expressed in terms of operations performed by agents.
 Operations work on objects (defined in the object model): they can create objects, trigger object
state transitions and activate other operations (by sending an event).
 Operations can directly be expressed by stakeholders during the interviews.
 Operations can be identified by looking at all the existing requirements.

Operational Model
 Operations are represented as ovals.
 Concerned objects are connected to the operations by means of Input and Output links.
 Events are represented as those traffic signs that are used to indicate directions.
Completeness criteria
 To be complete, a process diagram must specify:
◦ The agents who perform the operations
◦ The input and output data for each operation.
◦ When operations are to be executed.
◦ All operations are to be justified by the existence of some requirements (through the
use of operationalization links).

Summary
 KAOS Operational model
 Operational model terminology
 Example
WEEK 11, SLIDE 02:
KAOS Responsibility Model
 The responsibility model contains all the responsibility diagrams.
 A responsibility diagram describes for each agent, the requirements and expectations that he’s
responsible for, or that have been assigned to him.
 To build a responsibility diagram, the analyst reviews the different requirements and
expectations in the goal model and assigns an agent to each of them.
 After all requirements and expectations are assigned a responsible agent, a diagram is
generated for each agent, listing all requirements and expectations that he’s been assigned.

Summary
 KAOS Responsibility model
 Responsibility model notations

WEEK 12, SLIDE 01:
Requirement Change Management
 Requirements get changed during the course of development. It is almost impossible to stop the
requirements from changing. Different software development approaches tackle changing
requirement in different ways. Unlike Waterfall or document driven approaches of software
development, agile methodologies welcome change during the course of software development
but at the same time manage the changes in a systematic manner.
Agenda
 Overview
 Reasons for Requirements Changes
 Agile Manifesto
 Different Form of Agile, and their working
 Rational Unified Process
 Requirement Change Management in Agile
 Tools
Overview
 Importance/Significance
 Reasons for Requirements Changes
 Lack of domain knowledge at start
 Inconsistent requirements
 Change in customer prioritization
 Change in platform or environment
 Change due to expensiveness or difficult to implement
 The changes in organization
Agile Manifesto
 Agile focus and prefer more on individuals capabilities and expertise and their interaction rather
than tools, techniques and processes.

 Agile concentrate to have working application rather than formality of having large
documentation.
 Agile highly contemplate to have a very close relationship with customer in terms of continuous
and constant conversation rather than contract negotiation.
 Agile assures to adopt and respond frequently over change request rather than following a plan.
Extreme Programming (XP)
 Extreme Programming is the most famous agile technique. XP use story cards for elicitation. A
user story is the description that provides business value to the customer
 These rules are described below:
 The Planning Game
 Small Releases
 Metaphor
 Simple Design
 Tests
 Refactoring
 Pair Programming
 Collective Ownership
 Continuous Integration
 40-hour Week
 On-site customer
 Coding Standard
Extreme Programming (XP)

Scrum
 Scrum is another popular agile technique used to develop and manage software. The following
figure explains the activities performed in Scrum.
Rational Unified Process
 RUP---- Document Driven approach
 RUP Phases, RUP Disciplines
 Extensive planning, Codified Process, Heavy Documentation , Big Design up Front
 Strengths:
• Straightforward, methodical and structured nature, Predictability, stability and
high assurance
 Weaknesses
• Slow adaptation to rapidly changing business requirements
• A tendency to be over budget

• A tendency to behind schedule
• Failed to provide dramatic progress in productivity, simplicity and reliability
 XP and Scrum-- Agile Software Development Approaches
 Iterative and Incremental development, Customer collaboration, Frequent Delivery,
Light and fast development, Light documentation
 Strengths:
• Short development cycle, Higher customer satisfaction, Low bug rates, Quick
adaptation to rapidly changing requirements
• Highest Priority Work ,Constant Feedback, Control over Cost and Schedule
 Weaknesses
• Significant document reduction, Heavy dependence on individual knowledge,
Not suitable for critical safety systems, Not suitable for large scale systems,
Frequent change effect cost and schedule, Managed prioritization,
Organizational structure
Agile (XP and Scrum) requirements change management process
 The agile change management process handles changes in the beginning of each iteration of the
development cycle. It may be a sprint in Scrum or iteration in XP and so on. The key
stakeholders in change management process are the managers, developing team and off course
customers or product owner.
 As agile’s development period is considerably short for a particular iteration therefore it is
understood that all the requirements cannot be implemented in one go therefore there is a pile
or stack of requirements and the relevant stakeholders have to decide which requirements to
implement in the one iteration. Therefore the prioritization is also a continuous process in agile
development and the requirement stack is constantly updated as a result of update.
Change Management Process
 This aspect of Agile shows a different picture from that of traditional development where
requirements are collected once and changes made in that requirement set are rare. Here agile
is welcoming the change even after every iteration. Therefore agile is gaining wide acceptance in
today’s development where we also have high speed development environments.
Change Management Process

Lifecycle of change management in agile
 Start: In the start of each iteration, the team takes the highest priority requirement that can be
completed in the specified iteration period. This requirement which is now going to be
implemented is well understood with the help of customer and other related stakeholders and
documents etc. Necessary planning, documentation or modeling can also be done at this stage
so as to achieve the goal within the specified time and budget.
 Middle: During development they may take help from customer as well as from other relevant
stakeholders to have better understanding of the requirement. The aim is to build the software
that best meets the requirement.
 End: The working product developed can be deployed and it is preferable to deploy so as to take
the feedback from the end-users. The acceptance can also be run on the developed software so
that the necessary quality can also be ensured.
What Kind of Tool Do We Need?
 Word processor (Microsoft Word with templates…)
 Spreadsheet (Microsoft Excel…)
 Industrial-strength, commercial RM tools
 IBM/Telelogic DOORS, IBM Requisite Pro, Borland CaliberRM…
 Internal tools
 GenSpec (Hydro-Quebec)…

 Open source RM tools
 OSRMT: http://sourceforge.net/projects/osrmt
 Bug tracking tools (free or not)
 Bugzilla…
 Collaboration tools (free or not)
 TWiki…
WEEK 13, SLIDE 01:
Requirement Change Management Process
Comparison between Agile and Conventional Philosophy
 Both Agile and Document driven (companies following traditional approaches) companies face
similar issues with respect to requirements management but they use to handle it in different
ways. Some of the differences between these two approaches that have been identified as a
result of a study are explained below:
 Changing requirements (88%--13%):
 Reason for Requirement Change(knowledge Deepening):

Comparison
 Requirements Gathering Process(complete Specification/incrementally):
 Means of Communication (document/Onsite customer):
 Contracts with Clients(Strict/flexible):
 Attitudes towards Change(Difficult task/Welcome):
 Relationship with Customer(satisfactory/Close):
Freezing the Requirements
 Embracing requirement changes in Agile does not mean that requirement could be changed at
any stage of the software development process. What it really means is that unlike traditional
approaches like waterfall model where you do not have the privilege to request requirement
changes after the start of development cycle, here in agile the customer or the product owner
have an opportunity to add, modify or remove any requirement from the requirement stack.
 In fact Agile has laid down a process in every technique to accept change in an organized way for
next iteration instead of forcing to implement the new requirement in the current release.
 XP and Open UP allows accepting change to a certain extent during the development iteration
but recommends suggesting the requirement for next iteration.
Requirements Prioritization
 Nature of Agile development lifecycle demands
 Stakeholders status in the beginning
 feedback after every development iteration
 agile development framework allows the stakeholders to re-prioritize the requirements
 factors like market uncertainty, technical uncertainty, project duration and project budget that
demands that the requirements should be analyzed and re-prioritized
Value Oriented Prioritization
 Many studies have been carried out to propose good and scientific methods of prioritization
 One of the techniques for requirement prioritization was named as “Value Oriented
Prioritization”. This technique suggests that the company or the stakeholders should identify the
business value areas like Sales, Marketing, Strategic, Customer Retention etc. Then a positive
numeric value should be associated with each of these business value areas.

 After that, values are also assigned to each requirement after negotiation and consultation with
all the relevant stakeholders.
 Along with identifying the business value areas, the associated risks should also be identified
and a certain negative value should also be assigned to each risk as shown in fig.
Value Oriented Prioritization
 Then all the requirements are listed and given a numeric value against business value areas as
well as to the risk associated with that business value. In this way the weight of each
requirement can be calculated against each business value area and similarly the weight of risks
can also be identified. The final weight of a requirement can be calculated by subtracting the
sum of weights of the risks from the sum of weights of business values against each
requirement.
Example

Evaluation
 Requirements Evaluation from End user’s perspective
 Usability
 Usability Evaluation
 Usability Evaluation Methods
 The process of systematically collecting data that informs us about what it is like for a particular
or group of users to use a product for a particular task in a certain type of environment.
Why, what, where, and when to evaluate:
 Why: to check those users can use the product and that they like it.
 What: Conceptual model, early prototypes of a new system and later, more complete
prototypes.
 Where: in natural and laboratory settings.
 When: throughout design; finished products can be evaluated to collect information to inform
new products.
Usability
Usability has been defined by the International Standards Organization (ISO) as “the extent to which the
product can be used by specified users to achieve specified goals with
 effectiveness
 efficiency
 satisfaction
Usability Evaluation
 Metrics used to measure Usability:
 1. Time to complete a task
3. Fraction of task completed
4. Fraction of task completed in a given time
5. Number of errors
6. Time spent on errors
Usability Evaluation Methods
 Testing

 Inspection
 Inquiry
WEEK 14, SLIDE 01:
Introduction
 What is traceability?
◦ “The degree to which a relationship can be established between two or more products
of the development process, especially products having a predecessor-successor or
master-subordinate relationship to one another.” [IEEE-610]
 Requirements Traceability:
◦ The requirements traceability is the ability to describe and follow the life of a
requirement, in both a forward and backward direction.
Requirement Traceability (RT)
 Why requirement Traceability
◦ Finding missing requirements
◦ Finding unnecessary requirements
◦ Certification and compliance
◦ Change impact analysis
◦ Maintenance and
◦ Project tracking etc.

Classification of Requirement Tracibility

Classification of RT

Categories of requirement traceability

How is tracing performed?
 Each element is given a unique identifier
◦ Element – requirement, design attribute, test, etc
 Linkages done manually and managed by a CASE tool
 Traceability tables are made
◦ Matrix
Traceability matrix
 A traceability matrix is a document that co-relates any two-baseline documents that require a
many-to-many relationship to check the completeness of the relationship.
 It is used to track the requirements and to check the current project requirements are met.
 Types of Traceability Matrix
 Forward traceability
 Backward or reverse traceability
 Bi-directional traceability ( Forward + Backward)
 Advantage of Requirement Traceability Matrix
 It confirms 100% test coverage
 It highlights any requirements missing or document inconsistencies
 It shows the overall defects or execution status with a focus on business requirements
Requirement traceability matrix

Requirement traceability Tools
 CASE Tools
 Characteristics
◦ Hypertext linking
◦ Unique identifiers
◦ Syntactical similarity coefficients
 Problems
◦ Hypertext linking and syntactical similarity does not consider context
◦ Unique identifiers do not show requirement information
◦ Choosing architecture view and classification schemas will always be manual
Caliber-RM
 Caliber-RM
◦ Centralized repository
◦ Requirements traceability across the lifecycle
◦ Impact analysis

Rational Dynamic Object Oriented Requirements System(DOORS)
 DOORS
◦ Tele logic
◦ “capture, link, trace, and manage”
◦ For large applications
References
 Software Requirements Third Edition by Karl Wiegers and Joy Beatty
 James D. Palmer
 Requirements Engineering: Processes and Techniques’ by G. Kotonya and I. Sommerville, John
Wiley & Sons, 1998

WEEK 15, SLIDE 01:
Verification and Validation
Verification:
 Process in which we check a product against its specifications.
 White box, black box testing
Validation:
 Process in which we check expectations of the users who will be using it.
 Inspection, Formal Technical Review
Defects
 software without any defects
 No, it is almost impossible to develop software without having any defect. Software and defects
go side-by-side during software development. It is impossible to build a product in first instance
without presence of any defects and these two cannot be separated.
Black box testing
 In this type of testing, a component or system is treated as a black box and it is tested for the
required behavior. This type of testing is not concerned with how the inputs are transformed
into outputs. As the system’s internal implementation details are not visible to the tester. He
gives inputs using an interface that the system provides and tests the output. If the outputs
match with the expected results, system is fine otherwise a defect is found.
Structural testing (white box)
 As opposed to black box testing, in structural or white box testing we look inside the system and
evaluate what it consists of and how is it implemented. The inner of a system consists of design,
structure of code and its documentation etc. Therefore, in white box testing we analyze these
internal structures of the program and devise test cases that can test these structures.
Defect Removal Process
 Steps you take to check the presence of the defects
 I will run the scenario as described in the bug report and try to reproduce the defect.
 If the defect is reproduced in the development environment, I will identify the root cause, fix it
and send the patch to the testing team along with a bug resolution report.

Cyclomatic complexity
 E = Number of Edges
 N = Number of Nodes
 V(G) = E - N + 2
WEEK 15, SLIDE 02:
Introduction
 What is requirement document?
◦ Software requirements specifications or SRS
◦ The requirements document is a formal document used to communicate the
requirements to customers, engineers and managers
 Requirements includes:
◦ The services and functions which the system should provide
◦ The constraints under which the system must operate
◦ Overall properties of the system
Requirement document
Users of the requirements
◦ System customers
◦ Managers
◦ System engineers
◦ System test engineers
◦ System maintenance engineers
How to Organize an SRS?
 Clients/developers may have their own way of organizing an SRS
 US Department of Defense
 NASA
 IEEE/ANSI 830-1993 Standard

 IEEE Std. 830-1998
Characteristics of good SRS
 Correct
 Unambiguous
 Complete
 Consistent
 Verifiable
 Modifiable
 Traceable
IEEE/ANSI Standard 830-1993
 Parts of IEEE/ANSI Standard 830-1993
 Introduction
 General description
 Specific requirements
 Appendices
 Index
Parts of IEEE/ANSI Standard 830-1993
 Introduction:
o 1.1 Purpose of the requirements document
o 1.2 Scope of the product
o 1.3 Definitions, acronyms, and abbreviations
o 1.4 References
o 1.5 Overview of the remainder of the document
 General description
o 2.1 Product perspective
o 2.2 Product functions
o 2.3 User characteristics
o 2.4 General constraints
o 2.5 Assumptions and dependencies

 Specific Requirements
o Covering functional, non-functional, and interface requirements.
o These should document external interfaces, functionality, performance
requirements, logical database requirements, design constraints, system attributes,
and quality characteristics
General discussion on IEEE Standard (IEEE/ANSI Standard 830-1993)
 It is good starting point for organizing requirements documents
 First two sections are introductory chapters about background and describe the system
in general terms
 The third section is the main part of the documents and the standard recognizes that
this section varies considerably depending on the type of the system
References
 IEEE Recommended Practice for Software Requirements Specifications
 ‘Requirements Engineering: Processes and Techniques’ by G. Kotonya and I.

Software Requirements and Specifications

More Related Content

What's hot

Similar to Software Requirements and Specifications

Recently uploaded

In this document

Software Requirements and Specifications