1. Software engineering lec4 Requirements

2. 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

3. 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

4. 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:

5. 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

6. 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

7. 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

8. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 8 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

9. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 9 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

10. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 10 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.

11. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 11 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.

12. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 12 How to describe as 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.

13. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 13 Use case diagrams

14. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 14 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.

15. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 15 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.

16. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 16 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.

17. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 17 Example of generalization, extension and inclusion

18. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 18 Example description of a use case

19. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 19 Example (continued)

20. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 20 Example (continued)

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

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

23. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 23 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

24. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 24 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

25. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 25 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.

26. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 26 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

27. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 27 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

28. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 28 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

29. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 29 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

30. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 30 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

31. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 31 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.

32. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 32 Types of Requirements Functional requirements Describe what the system should do Non-functional requirements Constraints that must be adhered to during development

33. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 33 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

34. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 34 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

35. © Lethbridge/Laganière 2005 Chapter 4: Developing requirements 35 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

36. 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.

37. 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?

38. 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)

39. 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.