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Inception

Inception. > Spring 2010, Amirkabir university, CS department. Amin Gheibi. Inception. A short initial step to answer: What is the vision and business case for this project? Feasible? Buy and/or build? Rough estimate of cost: Is it $10K-100K or in the millions? Should we proceed or stop?

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Inception

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  1. Inception > Spring 2010, Amirkabir university, CS department Amin Gheibi

  2. Inception • A short initial step to answer: • What is the vision and business case for this project? • Feasible? • Buy and/or build? • Rough estimate of cost: Is it $10K-100K or in the millions? • Should we proceed or stop? • Just investigate the high-level requirements (not a deep drilling)

  3. Inception • Inception may be very brief • It is absolutely feasible (you had a same project) • Stakeholder is determined

  4. Vision • Vision document (contractual): • Problem Statement • Stakeholder responsibility • Very high-level requirements and features to give the reader an understanding of the system to be developed • design constraints • User Description • User Environment

  5. Business Case • Business Case: • describe the business issue that the recommended project would solve • Describe the anticipated outcomes. “What are we aiming for?” • Summary of recommendations • Justify why the recommended project should be implemented • List and describe any assumptions • List and describe any limiting factors

  6. Requirement • Requirements: • capabilities and conditions to which the system—must conform • Challenge: How to find and record real requirement • Requirement Mang. • It is not waterfall attitude (freezing requirements) • a systematic approach to finding, documenting, organizing, and tracking the changing

  7. Requirement

  8. Requirement

  9. Requirement

  10. Requirement

  11. No. 1 suspect

  12. Type of req. (Book’s categories) • Functional: • features, capabilities, security • Usability: • human factors, help, documentation • Reliability: • frequency of failure, recoverability, predictability • Performance: • response times, accuracy, availability, resource usage.

  13. Type of req. (Book’s categories) • Supportability: • adaptability, maintainability, internationalization, configurability. • It is helpful to use this kind of categories as a checklist for requirements coverage, to decrease the risk • Some of these requirements are quality attributes, or functional vs. non-functional

  14. Req. record • Functional requirements are explored and recorded in the Use-Case Model • Other requirements can be recorded in the use cases they relate to, or in the Supplementary Specifications artifact.

  15. Use Case • an excellent technique to understand and describe requirements is writing use cases: stories of using system • The best way to capture customers’ need is the simplest and most familiar one (especially for cusomer Bcz they can contribute)

  16. Example (informal format) • We need a structured format to capture requirements

  17. Definitions • Actor • A person, a system, or an organization with behavior: a cashier, tax calculator, inventory system … • Scenario (Use case instance) • a specific sequence of actions and interactions between actors and the system under discussion • Use case • a collection of related success and failure scenarios that describe actors using a system to support a goal.

  18. Example (Casual format)

  19. Focus in writing use cases • How can we use system to fulfill user’s goal or answer his need? Add value to user • Don’t look at them as laundry list of system’s functions • Black-box use case: • do not describe the internal workings of the system, • Rather, describe the system as having responsibilities

  20. Focus in writing use cases • it is possible to specify what the system must do (the functional requirements) without deciding how it will do it (the design)

  21. Degrees of formality • Brief (informal) • One paragraph about Main scenario • Casual: • Some paragraphs, also covers alternatives • Fully dressed • All steps and variations are written in detail, and there are supporting sections, such as preconditions and success guarantees

  22. Example • Open your book at page 50

  23. Questions ?

  24. Level of UC granularity • Which of these is a valid use case? • Negotiate a Supplier Contract • Handle Returns • Log In

  25. Elementary Business Process • A task performed by one person in one place at one time, in response to a business event (need), which adds measurable business value and leaves the data in a consistent state. • It’s not a single small step like • It doesn’t take days and multiple sessions

  26. Elementary Business Process • it is frequently useful to create separate "sub" use cases representing sub-tasks or steps within a base use case • To avoid duplication of the text • an EBP-level use case is called a user goal-level, to emphasize that it serves to fulfill a goal of the primary actor.

  27. Recommended procedure • Find the user goals • Define a use case for each • Rather than asking "What are the use cases?", one starts by asking: "What are your goals?" • Hierarchy of goals • Example: pp.62

  28. Subfunction • Is it always helpful? • The most common, valid motivation to express a subfunction goal as a use case is when the subfunction is repeated

  29. Primary actors • Use cases are defined to satisfy the user goals of the primary actors. • So to find use cases: • Choose the system boundary • Identify the primary actors • For each, identify their user goals • Define use cases that satisfy user goals (some exception e.g. CRUD)

  30. Choose the system boundary

  31. Identify the primary actors and goals • Actors: • Primary (call) • Supporting (is called) • Offstage (has some interest) • The team brainstorm and generate a mixture of both. Sometimes, goals reveal the actors, or vice versa. • Some reminder questions

  32. Actor-goal list

  33. Boundary • Why is the cashier, and not the customer, the primary actor in the use case Process Sale? • Why doesn’t the customer appear in the actor-goal list?

  34. Define Use Cases • Define one EBP-level use case for each user goal • Name use cases starting with a verb • A common exception is to collapse CRUD (create, retrieve, update, delete) into one CRUD use case, idiomatically called Manage <X>

  35. Iterative Improvement • Congratulations; Use Cases Have Been Written, and Are Imperfect • ongoing personal communication • XP Practice: User full-time on the project, in the project room

  36. Writing use cases in Essential Style • Focus on intention (goal) rather than interface • For example: log-in and authentication (maybe we offer fingerprint)

  37. Essential Style (example) • The design solution to these intentions and responsibilities is wide open

  38. Concrete Style (example) • Do not use them in early requirement analysis

  39. Use Case Diagram

  40. UCs in UP • Requirements are primarily recorded in use cases • Use cases are an important part of iterative planning. • Use-case realizations drive the design. • Use cases often influence the organization of user manuals • In one word: GOOD STARTING POINT

  41. Inception • Only 10% of the use cases written in any detail • Business Use Cases vs. System Use Cases

  42. Artifatcs

  43. Supplementary Spec.

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