Requirements Engineering. Materials: Pressman (chapters 8,9, 10, 11) Sommerville (Chapters 4, 5)

Transcription

1 Requirements Engineering Materials: Pressman (chapters 8,9, 10, 11) Sommerville (Chapters 4, 5)

2 Definition What is Requirement Engineering? Requirement: A function, constraint or other property that the system must provide to fill the needs of the system s intended user(s) Engineering: implies that systematic and repeatable techniques should be used Requirement engineering: a process by which requirements for a product are defined, managed and tested systematically

3 Definition What is Requirement Engineering? User Requirements: English statements of what the system is expected to provide to users (all users) and the constraints under which the system must operate System Requirements: detailed descriptions of system functions, services, and operational constraints (WHAT not the HOW)

4 Definition What is Requirement Engineering? Functional Requirements: Describes what the system should do (Function) Non-Functional Requirements: Describes everything that is not function related: Performance Reliability Cost/Resources Scaling Organizational aspects Environmental Regulatory Safety Security

5 Definition What is Requirement Engineering? Identifier Priority Requirement REQ1 5 The system shall keep the door locked at all times, unless commanded otherwise by authorized user. When the lock is disarmed, a countdown shall be initiated at the end of which the lock shall be automatically armed (if still disarmed). REQ2 2 The system shall lock the door when commanded by pressing a dedicated button. REQ3 5 The system shall, given a valid key code, unlock the door and activate other devices. REQ4 4 The system should allow mistakes while entering the key code. However, to resist dictionary attacks, the number of allowed failed attempts shall be small, say three, after which the system will block and the alarm bell shall be sounded. REQ5 2 The system shall maintain a history log of all attempted accesses for later review. REQ6 2 The system should allow adding new authorized persons at runtime or removing existing ones. REQ7 2 REQ8 1 REQ9 1 The system shall allow configuring the preferences for device activation when the user provides a valid key code, as well as when a burglary attempt is detected. The system should allow searching the history log by specifying one or more of these parameters: the time frame, the actor role, the door location, or the event type (unlock, lock, power failure, etc.). This function shall be available over the Web by pointing a browser to a specified URL. The system should allow filing inquiries about suspicious accesses. This function shall be available over the Web.

6 Why is Requirements Engineering hard?

7 Why is it Important? Use Defines the commitment between the clients and the delivery organiza8on, along with budget and schedule May be set upfront or evolve incrementally 60% of projects face complex domains Defines the acceptance criteria ~45% of project failures involve requirements phase issues (Chaos Study) Incomplete requirements (13%) Lack of user involvement (12%) Changing specificakons (9%) UnrealisKc expectakons (10%) Risks Each individual understands the same statement differently Clear idenkficakon of Minimal Required FuncKonality Perceived versus Actual Agreements Don t lose sight that at the end of the day, it s about what gets delivered. But if you don t know where you are going, it s hard to aim right.

8 Where does it fit in the Process? System Requirements SpecificaKon and Modeling Specifica8on User Requirements SpecificaKon Business Requirements SpecificaKon Start Elicita8on User Requirements ElicitaKon System Requirements ElicitaKon Feasibility Study Prototypes and Models Valida8on Source: Sommerville, So#ware Engineering, 10 th Ed, Fig 4.6

9 How do you do it? Process? Aspect- Oriented Requirements Object- Oriented Analysis & Design Requirements gathering Requirements analysis Requirements specificakon Structured Analysis & Design Agile Development User Stories

10 How do you do it? Process? Source; h]p://old.sigchi.org/bullekn/ /h- johnson1.gif

11 How do you do it? Document it? Ad hoc Diagrams and Models Formal Specifications Math Notations Well Defined Modeling Paradigms UML (Unified Modeling Language) Finite State Machines Petri-Nets

12 Example Requirements Identifier Priority Requirement REQ1 5 The system shall keep the door locked at all times, unless commanded otherwise by authorized user. When the lock is disarmed, a countdown shall be initiated at the end of which the lock shall be automatically armed (if still disarmed). REQ2 2 The system shall lock the door when commanded by pressing a dedicated button. REQ3 5 The system shall, given a valid key code, unlock the door and activate other devices. REQ4 4 The system should allow mistakes while entering the key code. However, to resist dictionary attacks, the number of allowed failed attempts shall be small, say three, after which the system will block and the alarm bell shall be sounded. REQ5 2 The system shall maintain a history log of all attempted accesses for later review. REQ6 2 The system should allow adding new authorized persons at runtime or removing existing ones. REQ7 2 REQ8 1 REQ9 1 The system shall allow configuring the preferences for device activation when the user provides a valid key code, as well as when a burglary attempt is detected. The system should allow searching the history log by specifying one or more of these parameters: the time frame, the actor role, the door location, or the event type (unlock, lock, power failure, etc.). This function shall be available over the Web by pointing a browser to a specified URL. The system should allow filing inquiries about suspicious accesses. This function shall be available over the Web.

13 What are User Stories? Similar to system requirements but focus on user. Preferred tool for agile methods As a tenant, I can unlock the doors to enter my apartment. user-role (benefactor) capability business-value

14 User Stories Identifier User Story Size ST-1 As an authorized person (tenant or landlord), I can keep the doors locked at all times. 4 points ST-2 As an authorized person (tenant or landlord), I can lock the doors on demand. 3 pts ST-3 The lock should be automatically locked after a defined period of time. 6 pts ST-4 As an authorized person (tenant or landlord), I can unlock the doors. (Test: Allow a small number of mistakes, say three.) 9 points ST-5 As a landlord, I can at runtime manage authorized persons. 10 pts ST-6 As an authorized person (tenant or landlord), I can view past accesses. 6 pts ST-7 As a tenant, I can configure the preferences for activation of various devices. 6 pts ST-8 As a tenant, I can file complaint about suspicious accesses. 6 pts

15 How do you know you have a correct requirement set? How to Validate/Verify? Clear and Unambiguous standard structure has only one possible interpretation Correct: contributes to a real need Understandable: A reader can easily understand the meaning of the requirement Verifiable: can be tested Complete Flaty PowetPoint Presentation

16 How do you do it? Process Management? Work backlog Estimated work duration 1) ST-4: Unlock 15 days (9pts) 2) ST-2: Lock 5 days (3pts) 3) ST-5: Manage Users 16 days (10pts) Items pulled by the team into an iteration 4) ST-7: Preferences 10 days (6pts) 5) ST-6: View History 10 days (6pts) 6) ST- Work items 21 days 1st iteration 2nd iteration n-th iteration List prioritized by the customer 5 days Estimated completion date Time

17 Class Assignment: Requirement Engineering Group: agree on a tool for requirement engineering. We recommend, Confluence Individual: Create an account or log into Confluence make sure you have an account setup for communication and team Group (sub-groups): create list of requirements based on your meetings and notes Group (project manager): Chart out the requirements Group (usability): Chart out a plan for usability testing of the different requirements Deliverables per group on canvas: account info link to requirements in the tool Gantt chart (project manager) plan for usability (usability)