1. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 1 Software Engineering: A Practitioner’s Approach, 6/e Chapter 7 Requirements Engineering Software Engineering: A Practitioner’s Approach, 6/e Chapter 7 Requirements Engineering copyright © 1996, 2001, 2005 R.S. Pressman & Associates, Inc. NOTE: Some slides referenced from: Ian Sommerville Slides for Software Engineering.

2. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 2 What is a requirement? It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification It may range from a high-level abstract statement of a service or of a system constraint to a detailed mathematical functional specification This is inevitable as requirements may serve a dual function This is inevitable as requirements may serve a dual function May be the basis for a bid for a contract - therefore must be open to interpretation May be the basis for a bid for a contract - therefore must be open to interpretation May be the basis for the contract itself - therefore must be defined in detail May be the basis for the contract itself - therefore must be defined in detail Both these statements may be called requirements Both these statements may be called requirements

3. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 3 Requirements Definition Should specify external behavior of the system so the requirements should not be defined using a computational model Should specify external behavior of the system so the requirements should not be defined using a computational model Includes functional and non-functional requirements Includes functional and non-functional requirements Functional requirements are statements of the services that the system should provide Functional requirements are statements of the services that the system should provide Non-functional requirements are constraints on the services and functions offered by the system Non-functional requirements are constraints on the services and functions offered by the system

4. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 4 Wicked Problems Most large software systems address wicked problems Most large software systems address wicked problems Problems which are so complex that they can never be fully understood and where understanding develops during the system development Problems which are so complex that they can never be fully understood and where understanding develops during the system development Therefore, requirements are normally both incomplete and inconsistent Therefore, requirements are normally both incomplete and inconsistent

5. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 5 Requirements Engineering-I Inception—ask a set of questions that establish … Inception—ask a set of questions that establish … basic understanding of the problem basic understanding of the problem the people who want a solution the people who want a solution the nature of the solution that is desired, and the nature of the solution that is desired, and the effectiveness of preliminary communication and collaboration between the customer and the developer the effectiveness of preliminary communication and collaboration between the customer and the developer Elicitation—elicit requirements from all stakeholders Elicitation—elicit requirements from all stakeholders Elaboration—create an analysis model that identifies data, function and behavioral requirements Elaboration—create an analysis model that identifies data, function and behavioral requirements Negotiation—agree on a deliverable system that is realistic for developers and customers Negotiation—agree on a deliverable system that is realistic for developers and customers

6. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 6 Requirements Engineering-II Specification—can be any one (or more) of the following: Specification—can be any one (or more) of the following: A written document A written document A set of models A set of models A formal mathematical A formal mathematical A collection of user scenarios (use-cases) A collection of user scenarios (use-cases) A prototype A prototype Validation—a review mechanism that looks for Validation—a review mechanism that looks for errors in content or interpretation errors in content or interpretation areas where clarification may be required areas where clarification may be required missing information missing information inconsistencies (a major problem when large products or systems are engineered) inconsistencies (a major problem when large products or systems are engineered) conflicting or unrealistic (unachievable) requirements. conflicting or unrealistic (unachievable) requirements. Requirements management Requirements management

7. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 7 Inception Identify stakeholders Identify stakeholders “who else do you think I should talk to?” “who else do you think I should talk to?” Recognize multiple points of view Recognize multiple points of view Work toward collaboration Work toward collaboration The first questions The first questions Who is behind the request for this work? Who is behind the request for this work? Who will use the solution? Who will use the solution? What will be the economic benefit of a successful solution What will be the economic benefit of a successful solution Is there another source for the solution that you need? Is there another source for the solution that you need?

8. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 8 Eliciting Requirements meetings are conducted and attended by both software engineers and customers meetings are conducted and attended by both software engineers and customers rules for preparation and participation are established rules for preparation and participation are established an agenda is suggested an agenda is suggested a "facilitator" (can be a customer, a developer, or an outsider) controls the meeting 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 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 the goal is to identify the problem to identify the problem propose elements of the solution propose elements of the solution negotiate different approaches, and negotiate different approaches, and specify a preliminary set of solution requirements specify a preliminary set of solution requirements

9. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 9 Eliciting Requirements

10. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 10 Elicitation Work Products a statement of need and feasibility. a statement of need and feasibility. a bounded statement of scope for the system or product. a bounded statement of scope for the system or product. a list of customers, users, and other stakeholders who participated in requirements elicitation a list of customers, users, and other stakeholders who participated in requirements elicitation a description of the system’s technical environment. a description of the system’s technical environment. a list of requirements (preferably organized by function) and the domain constraints that apply to each. a list of requirements (preferably organized by function) and the domain constraints that apply to each. a set of usage scenarios that provide insight into the use of the system or product under different operating conditions. a set of usage scenarios that provide insight into the use of the system or product under different operating conditions. any prototypesdeveloped to better define requirements any prototypes developed to better define requirements.

11. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 11Use-Cases A collection of user scenarios that describe the thread of usage of a system A collection of user scenarios that describe the thread of usage of a system Each scenario is described from the point-of-view of an “actor”—a person or device that interacts with the software in some way Each scenario is described from the point-of-view of an “actor”—a person or device that interacts with the software in some way Each scenario answers the following questions: Each scenario answers the following questions: Who is the primary actor, the secondary actor (s)? Who is the primary actor, the secondary actor (s)? What are the actor’s goals? What are the actor’s goals? What preconditions should exist before the story begins? What preconditions should exist before the story begins? What main tasks or functions are performed by the actor? What main tasks or functions are performed by the actor? What extensions might be considered as the story is described? What extensions might be considered as the story is described? What variations in the actor’s interaction are possible? What variations in the actor’s interaction are possible? What system information will the actor acquire, produce, or change? What system information will the actor acquire, produce, or change? Will the actor have to inform the system about changes in the external environment? Will the actor have to inform the system about changes in the external environment? What information does the actor desire from the system? What information does the actor desire from the system? Does the actor wish to be informed about unexpected changes? Does the actor wish to be informed about unexpected changes?

12. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 12 Use-Case Diagram

13. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 13 Building the Analysis Model Elements of the analysis model Elements of the analysis model Scenario-based elements Scenario-based elements Functional—processing narratives for software functions Functional—processing narratives for software functions Use-case—descriptions of the interaction between an “actor” and the system Use-case—descriptions of the interaction between an “actor” and the system Class-based elements Class-based elements Implied by scenarios Implied by scenarios Behavioral elements Behavioral elements State diagram State diagram Flow-oriented elements Flow-oriented elements Data flow diagram Data flow diagram

14. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 14 Class Diagram From the SafeHome system …

15. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 15 State Diagram

16. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 16 Negotiating Requirements Identify the key stakeholders Identify the key stakeholders These are the people who will be involved in the negotiation These are the people who will be involved in the negotiation Determine each of the stakeholders “win conditions” Determine each of the stakeholders “win conditions” Win conditions are not always obvious Win conditions are not always obvious Negotiate Negotiate Work toward a set of requirements that lead to “win-win” Work toward a set of requirements that lead to “win-win”

17. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 17 Reasons we need to negotiate Large software systems must improve the current situation. It is hard to anticipate the effects that the new system will have on the organization Large software systems must improve the current situation. It is hard to anticipate the effects that the new system will have on the organization Different users have different requirements and priorities. There is a constantly shifting compromise in the requirements Different users have different requirements and priorities. There is a constantly shifting compromise in the requirements System end-users and organizations who pay for the system have different requirements System end-users and organizations who pay for the system have different requirements Prototyping is often required to clarify requirements Prototyping is often required to clarify requirements

18. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 18 Requirements Document Structure Purpose Purpose Overall Description Overall Description System Features (Functional Requirements/Use Cases) System Features (Functional Requirements/Use Cases) External Interface Requirements External Interface Requirements User interface requirements or standards User interface requirements or standards Hardware interfaces to other systems Hardware interfaces to other systems Software interfaces to other systems Software interfaces to other systems Communication Interfaces Communication Interfaces Non-functional Requirements Non-functional Requirements Appendices Appendices See SRS Template on the CS421 project page (provided by http://www.processimpact.com/). See SRS Template on the CS421 project page (provided by http://www.processimpact.com/).

19. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 19 Requirements Rationale It is important to provide rationale with requirements (this will be part of our description in the requirements specification document). It is important to provide rationale with requirements (this will be part of our description in the requirements specification document). This helps the developer understand the application domain and why the requirement is stated in its current form This helps the developer understand the application domain and why the requirement is stated in its current form Particularly important when requirements have to be changed. The availability of rationale reduces the chances that change will have unexpected effects Particularly important when requirements have to be changed. The availability of rationale reduces the chances that change will have unexpected effects

20. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 20 Non-Functional Requirement Types Product requirements Product requirements Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc. Requirements which specify that the delivered product must behave in a particular way e.g. execution speed, reliability, etc. Organizational requirements Organizational requirements Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc. Requirements which are a consequence of organisational policies and procedures e.g. process standards used, implementation requirements, etc. External requirements External requirements Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc. Requirements which arise from factors which are external to the system and its development process e.g. interoperability requirements, legislative requirements, etc.

21. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 21 Non-Functional Requirement Examples Product requirement Product requirement 4.C.8 It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set. 4.C.8 It shall be possible for all necessary communication between the APSE and the user to be expressed in the standard Ada character set. Organizational requirement Organizational requirement 9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP- STAN-95. 9.3.2 The system development process and deliverable documents shall conform to the process and deliverables defined in XYZCo-SP- STAN-95. External requirement External requirement 7.6.5 The system shall provide facilities that allow any user to check if personal data is maintained on the system. A procedure must be defined and supported in the software that will allow users to inspect personal data and to correct any errors in that data. 7.6.5 The system shall provide facilities that allow any user to check if personal data is maintained on the system. A procedure must be defined and supported in the software that will allow users to inspect personal data and to correct any errors in that data.

22. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 22 Requirements must be testable Requirements should be written so that they can be objectively verified Requirements should be written so that they can be objectively verified The problem with this requirement is its use of vague terms such as ‘errors shall be minimized” The problem with this requirement is its use of vague terms such as ‘errors shall be minimized” The system should be easy to use by experienced controllers and should be organized in such a way that user errors are minimized. The system should be easy to use by experienced controllers and should be organized in such a way that user errors are minimized. The error rate should be been quantified The error rate should be been quantified Experienced controllers should be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users should not exceed two per day. Experienced controllers should be able to use all the system functions after a total of two hours training. After this training, the average number of errors made by experienced users should not exceed two per day.

23. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 23 Requirements must be testable

24. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 24 System Level Requirements Some requirements place constraints on the system as a whole rather than specific system functions Some requirements place constraints on the system as a whole rather than specific system functions Example Example The time required for training a system operator to be proficient in the use of the system must not exceed 2 working days. The time required for training a system operator to be proficient in the use of the system must not exceed 2 working days. These may be emergent requirements which cannot be derived from any single sub-set of the system requirements These may be emergent requirements which cannot be derived from any single sub-set of the system requirements

25. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 25 Requirements Validation Concerned with demonstrating that the requirements define the system that the customer really wants Concerned with demonstrating that the requirements define the system that the customer really wants Requirements error costs are high so validation is very important Requirements error costs are high so validation is very important Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error Fixing a requirements error after delivery may cost up to 100 times the cost of fixing an implementation error Prototyping is an important technique of requirements validation Prototyping is an important technique of requirements validation

26. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 26 Validating Requirements-I Is each requirement consistent with the overall objective for the system/product? Work with all parties on this question! Is each requirement consistent with the overall objective for the system/product? Work with all parties on this question! Have all requirements been specified at the proper level of abstraction? That is, do some requirements provide a level of technical detail that is inappropriate at this stage? Have all requirements been specified at the proper level of abstraction? That is, do some requirements provide a level of technical detail that is inappropriate at this stage? Is the requirement really necessary or does it represent an add-on feature that may not be essential to the objective of the system? Is the requirement really necessary or does it represent an add-on feature that may not be essential to the objective of the system? Is each requirement bounded and unambiguous? Is each requirement bounded and unambiguous? Does each requirement have attribution? That is, is a source (generally, a specific individual) noted for each requirement? Does each requirement have attribution? That is, is a source (generally, a specific individual) noted for each requirement? Do any requirements conflict with other requirements? Do any requirements conflict with other requirements?

27. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 27 Validating Requirements-II Is each requirement achievable in the technical environment that will house the system or product? Is each requirement achievable in the technical environment that will house the system or product? Is each requirement testable, once implemented? Is each requirement testable, once implemented? Does the requirements model properly reflect the information, function and behavior of the system to be built. Does the requirements model properly reflect the information, function and behavior of the system to be built. Has the requirements model been “partitioned” in a way that exposes progressively more detailed information about the system. Has the requirements model been “partitioned” in a way that exposes progressively more detailed information about the system. Have requirements patterns been used to simplify the requirements model. Have all patterns been properly validated? Are all patterns consistent with customer requirements? Have requirements patterns been used to simplify the requirements model. Have all patterns been properly validated? Are all patterns consistent with customer requirements?

28. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 28 Requirements Reviews Regular reviews should be held while the requirements definition is being formulated Regular reviews should be held while the requirements definition is being formulated Both client and contractor staff should be involved in reviews Both client and contractor staff should be involved in reviews Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage Reviews may be formal (with completed documents) or informal. Good communications between developers, customers and users can resolve problems at an early stage

29. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 29 Requirements Reviews Check Verifiability. Is the requirement realistically testable? Verifiability. Is the requirement realistically testable? Comprehensibility. Is the requirement properly understood? Comprehensibility. Is the requirement properly understood? Traceability. Is the origin of the requirement clearly stated? Traceability. Is the origin of the requirement clearly stated? Adaptability. Can the requirement be changed without a large impact on other requirements? Adaptability. Can the requirement be changed without a large impact on other requirements?

30. These courseware materials are to be used in conjunction with Software Engineering: A Practitioner’s Approach, 6/e and are provided with permission by R.S. Pressman & Associates, Inc., copyright © 1996, 2001, 2005 30 Quality Function Deployment Function deployment determines the “value” (as perceived by the customer) of each function required of the system Function deployment determines the “value” (as perceived by the customer) of each function required of the system Information deployment identifies data objects and events Information deployment identifies data objects and events Task deployment examines the behavior of the system Task deployment examines the behavior of the system Value analysis determines the relative priority of requirements Value analysis determines the relative priority of requirements