Chapter 4 Requirements Engineering

1. Chapter 4Requirements 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?