1. Software engineering lec3 Requirements

2. Contents Developing Requirements Domain analysis The starting point for software projects Defining the problem and the scope What is requirement? Type of requirement Use cases Techniques for gathering requirements Types of requirements document Reviewing requirements

3. Developing requirements Start thinking about particular problem Understand the problem  Domain analysis Gather information  To describe the problem  To describe solution How to gather and analyzing the problem

4. Domain analysis Used to learn background information  Sufficient information  Good decision about: Requirement analysis Engineering process Domain: general field of the problem business  Examples?  Ask the domain experts

5. Cont. Gather information about the problem domain:  Ask experts  Books  Documentations Interviewing Brainstorming You are not to be an expert in this domain What are the goods when you do this:

6. Cont. Faster development  Easy to communicate with the stakeholders Better system  Analysis leads to better abstraction and hence improve designs Anticipation of extension  More adaptable system  Future development  Emerging trends

7. Summary It is useful to write a summary Introduction Glossary General knowledge Customer and user The environment Tasks and procedures Competing software Similarities across domain and organization Do not write too much

8. Example: airlines reservation What are the required information?  Flight scheduling  Fares  Ticketing  Booking Study what:  Airline reservation business Travel agents Employees Laws and rules for govern this business What is competing for airlines systems  What currently available

9. Software project starting point AB DC Requirement must be determined Client have produced requirement New development Evolution of existing system

10. Cont. A and B greenfield development  Develop software from scratch C and D  Evolves existing system  Rather common situation A and C  Asked to do system B and D  Customer did the requirement analysis

11. Defining the problem and the scope Initial definition of the problem Problem is difficulty (user/customer) are facing

12. © Lethbridge/Laganière 2005Chapter 4: Developing requirements12 4.3 Defining the Problem and the Scope A problem can be expressed as: A difficulty the users or customers are facing, Or as an opportunity that will result in some benefit such as improved productivity or sales. The solution to the problem normally will entail developing software A good problem statement is short and succinct

13. © Lethbridge/Laganière 2005Chapter 4: Developing requirements13 Scenarios A scenario is an instance of a use case It expresses a specific occurrence of the use case — a specific actor... — at a specific time... — with specific data.

14. © Lethbridge/Laganière 2005Chapter 4: Developing requirements14 How to describe a single use case A. Name: Give a short, descriptive name to the use case. B. Actors: List the actors who can perform this use case. C. Goals: Explain what the actor or actors are trying to achieve. D. Preconditions: State of the system before the use case. E. Description: Give a short informal description. F. Related use cases. G. Steps: Describe each step using a 2-column format. H. Postconditions: State of the system in following completion.

15. © Lethbridge/Laganière 2005Chapter 4: Developing requirements15 Use case diagrams

16. © Lethbridge/Laganière 2005Chapter 4: Developing requirements16 Extensions Used to make optional interactions explicit or to handle exceptional cases. By creating separate use case extensions, the description of the basic use case remains simple. A use case extension must list all the steps from the beginning of the use case to the end. — Including the handling of the unusual situation.

17. © Lethbridge/Laganière 2005Chapter 4: Developing requirements17 Generalizations Much like superclasses in a class diagram. A generalized use case represents several similar use cases. One or more specializations provides details of the similar use cases.

18. © Lethbridge/Laganière 2005Chapter 4: Developing requirements18 Inclusions Allow one to express commonality between several different use cases. Are included in other use cases — Even very different use cases can share sequence of actions. — Enable you to avoid repeating details in multiple use cases. Represent the performing of a lower-level task with a lower-level goal.

19. © Lethbridge/Laganière 2005Chapter 4: Developing requirements19 Example of generalization, extension and inclusion

20. © Lethbridge/Laganière 2005Chapter 4: Developing requirements20 Example description of a use case

21. © Lethbridge/Laganière 2005Chapter 4: Developing requirements21 Example (continued)

22. © Lethbridge/Laganière 2005Chapter 4: Developing requirements22 Example (continued)

23. © Lethbridge/Laganière 2005Chapter 4: Developing requirements23 Example (continued)

24. © Lethbridge/Laganière 2005Chapter 4: Developing requirements24 Example (continued)

25. © Lethbridge/Laganière 2005Chapter 4: Developing requirements25 The modeling processes: Choosing use cases on which to focus Often one use case (or a very small number) can be identified as central to the system — The entire system can be built around this particular use case There are other reasons for focusing on particular use cases: — Some use cases will represent a high risk because for some reason their implementation is problematic — Some use cases will have high political or commercial value

26. © Lethbridge/Laganière 2005Chapter 4: Developing requirements26 The benefits of basing software development on use cases They can help to define the scope of the system They are often used to plan the development process They are used to both develop and validate the requirements They can form the basis for the definition of testcases They can be used to structure user manuals

27. © Lethbridge/Laganière 2005Chapter 4: Developing requirements27 Use cases must not be seen as a panacea The use cases themselves must be validated — Using the requirements validation methods. There are some aspects of software that are not covered by use case analysis. Innovative solutions may not be considered.

28. © Lethbridge/Laganière 2005Chapter 4: Developing requirements28 4.7 Some Techniques for Gathering and Analysing Requirements Observation Read documents and discuss requirements with users Shadowing important potential users as they do their work — ask the user to explain everything he or she is doing Session videotaping Interviewing Conduct a series of interviews — Ask about specific details — Ask about the stakeholder’s vision for the future — Ask if they have alternative ideas — Ask for other sources of information — Ask them to draw diagrams

29. © Lethbridge/Laganière 2005Chapter 4: Developing requirements29 Gathering and Analysing Requirements... Brainstorming Appoint an experienced moderator Arrange the attendees around a table Decide on a ‘trigger question’ Ask each participant to write an answer and pass the paper to its neighbour Joint Application Development (JAD) is a technique based on intensive brainstorming sessions

30. © Lethbridge/Laganière 2005Chapter 4: Developing requirements30 Gathering and Analysing Requirements... Prototyping The simplest kind: paper prototype. — a set of pictures of the system that are shown to users in sequence to explain what would happen The most common: a mock-up of the system’s UI — Written in a rapid prototyping language — Does not normally perform any computations, access any databases or interact with any other systems — May prototype a particular aspect of the system

31. © Lethbridge/Laganière 2005Chapter 4: Developing requirements31 Gathering and Analysing Requirements... Use case analysis Determine the classes of users that will use the facilities of this system (actors) Determine the tasks that each actor will need to do with the system

32. © Lethbridge/Laganière 2005Chapter 4: Developing requirements32 4.8 Types of Requirements Document Requirements documents for large systems are normally arranged in a hierarchy Requirements Specification xxxx xxxxxxx xxx xxxxxxxxxxx xxxxx xxxxxxxxxxxxx xxxxxxx xxx xxxxxxxxxxxxxxx Requirements Definition xxxx xxxxxxx xxx xxxxxxxxxxx xxxxx xxxxxxxxxxxxx xxxxxxx xxx xxxxxxxxxxxxxxx Requirements Specification xxxx xxxxxxx xxx xxxxxxxxxxx xxxxx xxxxxxxxxxxxx xxxxxxx xxx xxxxxxxxxxxxxxx Requirements Definition xxxx xxxxxxx xxx xxxxxxxxxxx xxxxx xxxxxxxxxxxxx xxxxxxx xxx xxxxxxxxxxxxxxx Requirements Specification xxxx xxxxxxx xxx xxxxxxxxxxx xxxxx xxxxxxxxxxxxx xxxxxxx xxx xxxxxxxxxxxxxxx Two extremes: An informal outline of the requirements using a few paragraphs or simple diagrams requirements definition A long list of specifications that contain thousands of pages of intricate detail requirements specification

33. © Lethbridge/Laganière 2005Chapter 4: Developing requirements33 Level of detail required in a requirements document How much detail should be provided depends on: — The size of the system — The need to interface to other systems — The readership — The stage in requirements gathering — The level of experience with the domain and the technology — The cost that would be incurred if the requirements were faulty

34. © Lethbridge/Laganière 2005Chapter 4: Developing requirements34 4.9 Reviewing Requirements Each individual requirement should — Have benefits that outweigh the costs of development — Be important for the solution of the current problem — Be expressed using a clear and consistent notation — Be unambiguous — Be logically consistent — Lead to a system of sufficient quality — Be realistic with available resources — Be verifiable — Be uniquely identifiable — Does not over-constrain the design of the system

35. © Lethbridge/Laganière 2005Chapter 4: Developing requirements35 Requirements documents... The document should be: — sufficiently complete — well organized — clear — agreed to by all the stakeholders Traceability:

36. © Lethbridge/Laganière 2005Chapter 4: Developing requirements36 Requirements document... A.Problem B.Background information C.Environment and system models D.Functional Requirements E.Non-functional requirements

37. © Lethbridge/Laganière 2005Chapter 4: Developing requirements37 Defining the Scope Narrow the scope by defining a more precise problem List all the things you might imagine the system doing — Exclude some of these things if too broad — Determine high-level goals if too narrow Example: A university registration system

38. © Lethbridge/Laganière 2005Chapter 4: Developing requirements38 4.4 What is a Requirement Requirement: A statement about the proposed system that all stakeholders agree must be made true in order for the customer’s problem to be adequately solved. Short and concise piece of information Says something about the system All the stakeholders have agreed that it is valid It helps solve the customer’s problem A collection of requirements is a requirements document.

39. © Lethbridge/Laganière 2005Chapter 4: Developing requirements39 4.5 Types of Requirements Functional requirements Describe what the system should do Non-functional requirements Constraints that must be adhered to during development

40. © Lethbridge/Laganière 2005Chapter 4: Developing requirements40 Functional requirements What inputs the system should accept What outputs the system should produce What data the system should store that other systems might use What computations the system should perform The timing and synchronization of the above

41. © Lethbridge/Laganière 2005Chapter 4: Developing requirements41 Non-functional requirements All must be verifiable Three main types 1. Categories reflecting: usability, efficiency, reliability, maintainability and reusability — Response time — Throughput — Resource usage — Reliability — Availability — Recovery from failure — Allowances for maintainability and enhancement — Allowances for reusability

42. © Lethbridge/Laganière 2005Chapter 4: Developing requirements42 Non-functional requirements 2. Categories constraining the environment and technology of the system. — Platform — Technology to be used 3. Categories constraining the project plan and development methods — Development process (methodology) to be used — Cost and delivery date - Often put in contract or project plan instead

43. © Lethbridge/Laganière 2005Chapter 4: Developing requirements43 4.6 Use-Cases describing how the user will use the system A use case is a typical sequence of actions that a user performs in order to complete a given task The objective of use case analysis is to model the system … from the point of view of how users interact with this system … when trying to achieve their objectives. A use case model consists of — a set of use cases — an optional description or diagram indicating how they are related

44. © Lethbridge/Laganière 2005Chapter 4: Developing requirements44 Use cases In general, a use case should cover the full sequence of steps from the beginning of a task until the end. A use case should describe the user’s interaction with the system... — not the computations the system performs. A use case should be written so as to be as independent as possible from any particular user interface design. A use case should only include actions in which the actor interacts with the computer.

45. © Lethbridge/Laganière 2005Chapter 4: Developing requirements45 Scenarios A scenario is an instance of a use case It expresses a specific occurrence of the use case — a specific actor... — at a specific time... — with specific data.

46. © Lethbridge/Laganière 2005Chapter 4: Developing requirements46 How to describe a single use case A. Name: Give a short, descriptive name to the use case. B. Actors: List the actors who can perform this use case. C. Goals: Explain what the actor or actors are trying to achieve. D. Preconditions: State of the system before the use case. E. Description: Give a short informal description. F. Related use cases. G. Steps: Describe each step using a 2-column format. H. Postconditions: State of the system in following completion.

47. © Lethbridge/Laganière 2005Chapter 4: Developing requirements47 Use case diagrams

48. © Lethbridge/Laganière 2005Chapter 4: Developing requirements48 Extensions Used to make optional interactions explicit or to handle exceptional cases. By creating separate use case extensions, the description of the basic use case remains simple. A use case extension must list all the steps from the beginning of the use case to the end. — Including the handling of the unusual situation.

49. © Lethbridge/Laganière 2005Chapter 4: Developing requirements49 Generalizations Much like superclasses in a class diagram. A generalized use case represents several similar use cases. One or more specializations provides details of the similar use cases.

50. © Lethbridge/Laganière 2005Chapter 4: Developing requirements50 Inclusions Allow one to express commonality between several different use cases. Are included in other use cases — Even very different use cases can share sequence of actions. — Enable you to avoid repeating details in multiple use cases. Represent the performing of a lower-level task with a lower-level goal.

51. © Lethbridge/Laganière 2005Chapter 4: Developing requirements51 Example of generalization, extension and inclusion

52. © Lethbridge/Laganière 2005Chapter 4: Developing requirements52 Example description of a use case

53. © Lethbridge/Laganière 2005Chapter 4: Developing requirements53 Example (continued)

54. © Lethbridge/Laganière 2005Chapter 4: Developing requirements54 Example (continued)

55. © Lethbridge/Laganière 2005Chapter 4: Developing requirements55 Example (continued)

56. © Lethbridge/Laganière 2005Chapter 4: Developing requirements56 Example (continued)

57. © Lethbridge/Laganière 2005Chapter 4: Developing requirements57 The modeling processes: Choosing use cases on which to focus Often one use case (or a very small number) can be identified as central to the system — The entire system can be built around this particular use case There are other reasons for focusing on particular use cases: — Some use cases will represent a high risk because for some reason their implementation is problematic — Some use cases will have high political or commercial value

58. © Lethbridge/Laganière 2005Chapter 4: Developing requirements58 The benefits of basing software development on use cases They can help to define the scope of the system They are often used to plan the development process They are used to both develop and validate the requirements They can form the basis for the definition of testcases They can be used to structure user manuals

59. © Lethbridge/Laganière 2005Chapter 4: Developing requirements59 Use cases must not be seen as a panacea The use cases themselves must be validated — Using the requirements validation methods. There are some aspects of software that are not covered by use case analysis. Innovative solutions may not be considered.

60. © Lethbridge/Laganière 2005Chapter 4: Developing requirements60 4.7 Some Techniques for Gathering and Analysing Requirements Observation Read documents and discuss requirements with users Shadowing important potential users as they do their work — ask the user to explain everything he or she is doing Session videotaping Interviewing Conduct a series of interviews — Ask about specific details — Ask about the stakeholder’s vision for the future — Ask if they have alternative ideas — Ask for other sources of information — Ask them to draw diagrams

61. Questions for this lecture What is meant by requirement engineering? Requirement engineering could be classified into different types list five ? What is the different between functional and non-functional requirements? If you are to develop a project involve in designing a system for ticket reservation. – List five (5) functional requirements for you system. – List five Non-functional requirements for your system.

62. Cont. What is purpose of doing a domain analysis? If you have been asked to improve a system for book store in your university. – Is your project a Greenfield project, and why? – Considering the four starting points in page 9. under which starting point, you can classify your project? – List four of the framework requirements in this project?

63. Cont. What are the eight (8) elements to describe a use case? Describe the following use cases: – Booking a ticket. – Canceling a booking in a flight – Adding a new book to the library – Student is taking a subject. (register for the subject)

64. Cont. Draw a use case diagram for the examples in the last question. In a student registration unit system: – Suggest three actors to this system – What are the proper information that could taken from the student to register for a new semester. Write three pages as analysis documentation for your project.