1. Object-Oriented Software Engineering Practical Software Development using UML and Java Chapter 4: Developing Requirements Based on Presentations LLOSENG (Lethbridge, Laganiere,2001, Williams 2001, Probert 2001)

2. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT2 Requirements Engineering Motto: "The hardest single part of building a software system is deciding what to build. No other part of the work so cripples the resulting system if done wrong. No other part is more difficult to rectify later." [Brooks 87]

3. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT3 4.1 Domain Analysis The process by which a software engineer learns about the domain to better understand the problem: The domain is the general field of business or technology in which the clients will use the software A domain expert is a person who has a deep knowledge of the domain Benefits of performing domain analysis: Faster development Better system Anticipation of extensions

4. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT4 Domain Analysis document A.Introduction B.Glossary C.General knowledge about the domain D.Customers and users E.The environment F.Tasks and procedures currently performed G.Competing software H.Similarities to other domains

5. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT5 4.2 The Starting Point for Software Projects green field project

6. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT6 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

7. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT7 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

8. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT8 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.

9. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT9 4.5 Types of Requirements Functional requirements Describe what the system should do Non-functional requirements Constraints that must be adhered to during development

10. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT10 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

11. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT11 Example of Functional Requirements A point of sale terminal must make it possible to record sales and payments. It is intended to be used in retail stores. The system includes hardware components and a software to run the system. The project goal is to develop the software.

12. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT12 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

13. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT13 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

14. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT14 Requirements Quality Requirements should be: 1. Correct. 2. Coherent - without: »Internal conflicts (contradictions, too general terms having various possible interpretations). »External conflicts (subsystem requirements conflicting with those of the systems). »Conflicts with standards. -Coherence can be verified - using formal approach by organizing requirements (in tables/dictionaries, keeping references) 3. Complete - having »all the required functions, »all the constraints, »all contingencies

15. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT15 Requirements Quality (1) Requirements should be: 4. Realists - according to budget, the existing technology, the required schedule 5. Necessary shouldn’t add non-necessary complications should be at the right level 6. Verifiable (testable) 7. Traceable (possibility to refer to requirements in a clear way). Non-functional requirements should be: Measurable. Ex. rather than “the system must be portable” “not more than 5% of the source code must be system dependent”. Linked to functional requirements affected.

16. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT16 4.6 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

17. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT17 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

18. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT18 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

19. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT19 Gathering and Analysing Requirements... Informal 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 More on use cases in Chapter 7

20. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT20 Example: Library System List a minimal set of use cases for the following actors in library system Borrower, Checkout Clerk, Librarian, Accounting System Borrower Borrower: Search for itens by title … By author … by subject Place a book on hold if it is checked out by somebody else Check the borrows personal information and list of book borrowed

21. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT21 Example: Library System (1) List a minimal set of use cases for the following actors in library system Borrower, Checkout Clerk, Librarian, Accounting System Checkout clerk All the Borrowers use cases, plus Check out an item for a borrower Check on an item that has been returns Renew an item Recorded that a fine has been paid Add a new borrower Update a borrower’s personal information (address, telephone number etc.

22. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT22 Example: Library System (2) List a minimal set of use cases for the following actors in library system Borrower, Checkout Clerk, Librarian, Accounting SystemLibrarian All the Borrowers and Checkout Clerk use cases, plus Add a new item to the collection Delete an item from the collection Change the information the system has recorded about an item Accounting System (acting autonomously) Obtain the amount of overdue fines paid by borrowers

23. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT23 4.7 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

24. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT24 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 (target audience) —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

25. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT25 4.8 Reviewing Requirements Each individual requirement should —Have benefits that outweigh the costs of development —Be important for the solution of the current problem -80% of the users problem can be solved with 20% of the work. —Be expressed using a clear and consistent notation -Example: rather than “The pharmacist will enter the patient ID number and then the patient’s medication record will be displayed”, write: “When the pharmacist enters the patient ID number, then system displays the patient’s medication record”. —Be unambiguous —Be logically consistent —Lead to a system of sufficient quality -All requirements should contribute to a system that is sufficiently usable, safe, efficient, reliable and maintainable. —Be realistic with available resources —Be verifiable —Be uniquely identifiable —Does not over-constrain the design of the system

26. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT26 Requirements documents... The document should be: —sufficiently complete —well organized —clear —agreed to by all the stakeholders Traceability:

27. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT27 Requirements document... A.Problem B.Background information C.Environment and system models D.Functional Requirements E.Non-functional requirements

28. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT28 4.9 Managing Changing Requirements Requirements change because: Business process changes Technology changes The problem becomes better understood Requirements analysis never stops Continue to interact with the clients and users The benefits of changes must outweigh the costs. —Certain small changes (e.g. look and feel of the UI) are usually quick and easy to make at relatively little cost. —Larger-scale changes have to be carefully assessed -Forcing unexpected changes into a partially built system will probably result in a poor design and late delivery Some changes are enhancements in disguise —Avoid making the system bigger, only make it better

29. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT29 4.10 Detailed Example GPS-base Automotive Navigation Assistant (GANA) A.Problem: GANA software will help drivers navigate by giving them directions to their destination.

30. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT30 4.10 Detailed Example (1) GPS-base Automotive Navigation Assistant (GANA) A.Problem: GANA software will help drivers navigate by giving them directions to their destination. B.Backgrounf information. See domain analysis document 1234 (not provided for the lectures) C.Environment and system models: GANA software is to run on special GANA hardware, described separately in document 1234. As described in document 1234, the hardware provides the following to the software a) GPS position information, b) a wireless Internet connection to a map data base, c) position of a trackball, d) a color 10cm x 10cm LCD screen, and f) in put from the car’s other systems containing data about speed and turning of the steering wheel. This requirements document describes the software only.

31. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT31 4.10 Detailed Example(2) GPS-base Automotive Navigation Assistant (GANA) D.Functional Requirements. 1.The system uses GPS information to calculate what map to display. The system also integrates information about the car’s speed and history of turns made in order to refine its accuracy about the vehicle’s location. 2.The system has two main interaction modes: In setup mode, the user consults maps and specifies the destination. In navigation mode,the system assists the user to navigate to the destination. 3.Setup mode 3.1 When the system is switched on, and the vehicle is stationary, it enters setup mode. If the vehicle is moving it enter navigation mode. For safety reasons you can not enter setup mode when the vehicle is moving

32. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT32 4.10 Detailed Example(3) GPS-base Automotive Navigation Assistant (GANA) 3.2 In setup mode, the system displays a map. The default map is in1:25000 scale and is centered on the user's current position. At this scale, the map covers a square with 2.5 km sides (6.25 km2). Maps are oriented so true north is at the top. 3.3 When the user's current position is within the visible range pf the map. The system always indicates it with a red arrow. The arrow points in the direction the user is heading. 3.4 The system also displays in orange ( computed in real time) the shortest route (in estimated travel time) from the current position to the center of the map. It will not be possible to display the entire route if the current position is not displayed. 3.5 When the user manipulates the trackball, the screen scrolls the map in the direction of rotation if the trackball, as if the user were grabbing the map.

33. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT33 4.10 Detailed Example(4) GPS-base Automotive Navigation Assistant (GANA) 3.6. The LCD screen displays the labels “Zoom Out”, “Zoom In”, “Go Current”, “Go destination”, “Set destination” and “Navigate” above the six buttons (from left to right). The buttons work as follows: Zoom In and Zoom Out display new maps. The scale of the map appears at the top right of the screen. There may be a delay retrieving a map, in which case the system displays a message ‘Retrieving map’. If the map or network is unavailable for any reason, the system displays: ‘Sorry. Map not available’ When the user presses Zoom In, the map scale is doubled so a smaller region is displayed, with more local detail. The maximum scale is 1:3125, means the map covers an area with 312.5 m sides (about 100,000 m2). If this scale is displayed, the Zoom In button is inoperative and its label appears in light gray.

34. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT34 4.10 Detailed Example(5) GPS-base Automotive Navigation Assistant (GANA) When the user presses Zoom Out, the map scale is divided by 2 so a larger region is displayed, with less local detail. The minimum scale is 1:102,400,000, which means the map covers an area with sides pf approximately 10.000 km. If this scale is displayed, the Zoom Out button is inoperative and its label appears on light gray. Note that the scales are only approximate die to spherical aberration. When the user presses Set Destination, the location at the center of the screen (marked by the end of the orange route) is set as the destination. The shortest route from the current position to the destination is highlighted in red and is adjusted as the car moves. The shortest route to the set destination (red) is shown on top of the shortest route to the center of the screen (orange), and hence has precedence. When the user presses Go Current, the map jumps so it is centered over the current location.

35. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT35 4.10 Detailed Example(6) GPS-base Automotive Navigation Assistant (GANA) When the user presses Go Destination, the map jumos so it is centerd over the destination. If no destination has been set, The destination defoults to the current location. When the user presses Navigate or the vehicle starts moving, the system enters navigation mode described bellow. 4. Navigation mode 4.1 A detailed map is never displayed in navigation mode since the user would not be able to concentrate on driving while looking at the map. 4.2 In no destination has been set, the system just displays the name of the cirrent highway or street and municipality in large font. 4.3 In addition if a destination has been serm the system displays the following in a very large font: -An arrow ponting up if the driver sgiuld do, in the follokwing format:’Turn at and on towards.

36. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT36 4.10 Detailed Example(7) GPS-base Automotive Navigation Assistant (GANA) -The destination municipality (or address if within), the distance remaining, the expected tome remaining and the expected arrival time 4.4 The turning arrows and instructions are displayed as soon as possible as long as they cannot be interpreted ambiguously. So, for example a left turn would only appear when the driver must tale the next left turn. 4.5 The system displays the labels Speak Now, Volume Up, Volume Down, Guide On, Guide Off and Setup above the six buttons (from left to right). The buttons work as follows -Speak Now Produces a computer-generated voice, reading the instructions that are on display. Every time the user presses the button. Any reading in progress is cancelled and the instructions are immediately read again starting from the beginning -Volume Up and Volume Down adjust sound output.

37. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT37 4.10 Detailed Example(8) GPS-base Automotive Navigation Assistant (GANA) -Speak Now Produces a computer-generated voice, reading the instructions that are on display. Every time the user presses the button. Any reading in progress is cancelled and the instructions are immediately read again starting from the beginning -Volume Up and Volume Down adjust sound output. -Guide On causes a computer-generated voice to automatically read the instructions one minute in advance of any requited driver action, such as exiting the highway, being needed. Guide Off cancels this function; the user would have to read the screen or press Speak Now. In situations where navigational action is required more frequently than once a minute, the voice reads the next instructions as soon as the system detects that the driver has responded to the previous instructions. -Setup switches to setup mode if the car is stationary. If the car is not stationary, the Setup button is grayed out and is inactive.

38. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT38 4.10 Detailed Example(9) GPS-base Automotive Navigation Assistant (GANA) 4.6 If the driver does not respond as expected to the instructions, and takes a different route, the system immediately calculates a new route. E. Non-functional requirements. 1. The system will be robust in the case of failure of the Internet connection or failure to receive the GPS signal, maintaining whatever service it can. 2. The system will be designed in a flexible way such that changes in wireless Internet or GPS technology can be incorporated in future releases. 3. The system will be designed anticipating incorporation of input from an inertial navigation unit that would take over in cases where GPS signals fail.

39. WINTER 2004 SEG 3300 A&B – DR. R.L. PROBERT39 4.13 Difficulties and Risks in Domain and Requirements Analysis Lack of understanding of the domain or the real problem —Do domain analysis and prototyping Requirements change rapidly —Perform incremental development, build flexibility into the design, do regular reviews Attempting to do too much —Document the problem boundaries at an early stage, carefully estimate the time It may be hard to reconcile conflicting sets of requirements —Brainstorming, JAD sessions, competing prototypes It is hard to state requirements precisely —Break requirements down into simple sentences and review them carefully, look for potential ambiguity, make early prototypes