1. Chapter 4 Requirements Engineering

2. Requirements Engineering
It helps software engineers to better understand the problem they will work to solve
It encompasses the set of tasks that lead to an understanding of what the business impact of the software will be, what the customer wants?

3. Types of Requirements Functional Requirements
These are statements of services the system should provide, how the system should react to particular inputs and how the system should behave in particular situations
Non-Functional Requirements
These are constraints on the services or functions offered by the system. They include timing constraints, constraints on the development process and standards

4. Requirements Engineering Tasks
Requirements engineering provides the appropriate mechanism for understanding what the customer wants, analyzing need, assessing feasibility, managing requirements as they are transformed into an operational system and so on
Requirements engineering is accomplished through seven functions:
Inception
Elicitation
Elaboration
Negotiation
Specification
Validation
Management

5. Requirements Engineering Tasks - Inception
Inception—ask a set of questions that establish …
basic understanding of the problem
the people who want a solution
the nature of the solution that is desired, and
the effectiveness of preliminary communication and collaboration between the customer and the developer

6. Requirements Engineering Tasks - Elicitation
Ask the customer, the user, and others
What the objectives for the system?
What is to be accomplished?
How the system fits into the needs of the business?
How the system is to be used on a day-to-day basis?

7. Requirements Engineering Tasks - Elicitation
A number of problems that makes the requirements elicitation as a difficult task:
Problems of scope
The boundary of the system is ill-defined
Problems of understanding
The customers are not completely sure of what is needed?
Problems of volatility
The requirements change over time

8. Requirements Engineering Tasks - Elaboration
Elaboration is an analysis modeling action that is composed of a number of modeling and refinement tasks
The end-result of elaboration is an analysis model that defines the informational, functional, and behavioral domain of the problem

9. Requirements Engineering Tasks - Negotiation
It is common for different customers to propose conflicting requirements
The requirements engineer must reconcile these conflicts through a process of negotiation
Customers, users, and other stakeholders are asked to rank requirements and discuss conflicts in priority
Risks associated with each requirement are identified and analyzed
Rough “guestimates” of development effort are made and used to assess the impact of each requirement on project cost and delivery time

10. Requirements Engineering Tasks - Specification
A specification can be any on of the following:
A written document
A set of graphical model
A formal mathematical model
A collection of user scenarios
A prototype
The specification is the final work product produced by the requirements engineer
It serves as the foundation for subsequent software engineering activities

11. Requirements Engineering Tasks - Validation
Requirements validation examines the specification to ensure that all requirements have been stated unambiguously
The review team that validates requirements includes software engineers, customers, users, other stakeholders
A review mechanism that looks for
errors in content or interpretation
areas where clarification may be required
missing information
inconsistencies (a major problem when large products or systems are engineered)
conflicting or unrealistic (unachievable) requirements

12. Requirements Engineering Tasks – Requirements Management
Requirement management is a set of activities that help the project team identify, control, and track requirements and changes to requirements at any time as the project proceeds
Requirements management begins with identification. Once requirements are identified, traceability tables are developed

13. Requirements Engineering Tasks – Requirements Management
Features traceability table
shows how requirements relate to important customer observable system features
Source traceability table
identifies the source of each requirement
Dependency traceability table
indicates how requirements are related to one another
Subsystem traceability table
categorizes requirements by the subsystem that they govern
Interface traceability table
shows how requirements relate to both internal and external system interfaces

14. Initiating the Requirements Engineering Process - Inception
Identify stakeholders
“who else do you think I should talk to?”
Recognize multiple points of view
Work toward collaboration
The first questions
Who is behind the request for this work?
Who will use the solution?
What will be the economic benefit of a successful solution
Is there another source for the solution that you need?

15. Eliciting Requirements - Elicitation
Collaborative Requirements Gathering
In order to encourage a collaborative, team-oriented approach to requirements gathering, a team of stakeholders and developers work together to identify the problem, propose elements of the solution, negotiate different approaches, and specify a preliminary set of solution required

16. Eliciting Requirements - Elicitation
Guidelines for collaborative requirements gathering meeting:
Meetings are conducted and attended by both software engineer and customers
Rules for preparation and participation are established
An agenda is suggested that is formal enough to cover all important points but informal enough to encourage the free flow of ideas
A “facilitator” ( can be a customer, a developer, or an outsider) controls the meeting
A “definition mechanism” ( can be work sheets, flip charts, or wall stickers or an electronic bulletin board, chat room, or virtual forum) is used
The goal is
to identify the problem,
propose elements of the solution,
negotiate different approaches, and
specify a preliminary set of solution requirements

17. Eliciting Requirements - Elicitation
Quality Function Deployment (QFD)
Quality Function Deployment (QFD) is a technique that translates the needs of the customer into technical requirements for software
QFD concentrates on maximizing customer satisfaction from the software engineering process
QFD emphasizes an understanding of what is valuable to the customer and then deploys these values throughout the engineering process

18. Eliciting Requirements - Elicitation
Quality Function Deployment Many QFD concepts are applicable to requirements elicitation activity. They are:
Function deployment
is used to determine the value of each function that is required for the system
Information deployment
identifies both the data objects and events that the system must consume and produce
Task deployment
examines the behavior of the system within the context of its environment
Value analysis
is conducted to determine the relative priority of requirements determined during each of the three deployments

19. Elicitation Work Products
The work products produced as a consequence of requirements elicitation will vary depending on the size of the system.
The work product include:
A statement of need and feasibility
A bounded statement of scope for the system
A list of customers, users, and other stakeholders
A description of the system’s technical environment
A list of requirements (organized by function)
A set of usage scenarios that provide insight into the use of the system
Any prototype developed to better define requirements

20. Developing Use-Cases
The first step in writing a use-case is to define the set of “actors” that will be involved in the system
Actors are different people (or devices) that use the system or product within the context of the function and behavior that is to be described
Actors represent the roles that people play as the system operates
An actor is anything that communicates with the system or product and that is external to the system

21. Developing Use-Cases
Once actors have been defined, use-cases can be developed
The following questions should be answered by a use-case:
Who is the primary actor, secondary actor?
What are the actor’s goals?
What main tasks are performed by the actor?
What information does the actor desire from the system?

22. Building the Analysis Model
The analysis model is to provide a description of the required informational, functional, and behavioral domains for a computer-based system.
The model changes dynamically as software engineers learn more about the system to be built, and stakeholders understand more about what they really require

23. Building the Analysis Model
The elements of the analysis model
Scenario-based elements
The system is described from the user’s point of view using scenario based approach
Use-cases, use-case diagram, activity diagram
Class-based elements
Each usage scenario implies a set of “objects” that are manipulated as an actor interacts with the system
These objects are categorized into classes
Class diagram, collaboration diagram

24. Building the Analysis Model
Elements of analysis model (cond…)
Behavioral elements
The analysis model must provide modeling elements that depict behavior
State diagram, sequence diagram
Flow-oriented elements
Information is transformed as it flows through a computer-based system
Data-flow diagram

25. Use-Case Diagram

26. State Diagram

27. Negotiating Requirements
The customer and the developer enter into a process of negotiation, where the customer may be asked to balance functionality, performance, and other system characteristics against cost and time
The best negotiations strive for a “win-win” result. The customer wins by getting the system that satisfies the majority of the customer’s needs, and software team wins by working to realistic and achievable budgets and deadlines

28. Negotiating Requirements
The negotiating activities carried at the beginning of each software process iteration are:
Identification of the system or subsystem’s key stakeholders
These are the people who will be involved in the negotiation
Determination of the stakeholders’ “win conditions”
Win conditions are not always obvious
Negotiate of the stakeholders’ win conditions to reconcile them into a set of win-win conditions for all concerned
Work toward a set of requirements that lead to “win-win”

29. Validating Requirements
The requirements represented by the model are prioritized by the customer and grouped within requirements packages that will be implemented as software increments and delivered to the customer
A review of the analysis model addresses the following questions:
Is each requirement consistent with the overall objective for the system?
Have all requirements been specified at the proper level of abstraction?
Is each requirement bounded and unambiguous?

30. Validating Requirements
A review of the analysis model addresses the following questions: (cond…)
Do any requirements conflicts with other requirements?
Is each requirement testable, once implemented?
Does the requirements model properly reflect the information, function, and behavior of the system to be built?