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Evaluating Requirements

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Presentation on theme: "Evaluating Requirements"— Presentation transcript:

1 Evaluating Requirements

2 To improve the world – Designing software badly can harm the world To meet customers’ needs – Designing software badly can harm customers To get a paycheck – Designing software badly can get you fired To have some fun – Designing software badly just plain feels bad Why bother to do a good job when designing software?

3 Strengths of each requirements evaluation technique TechniqueEspecially good forWeaknesses Paper prototyping-Evaluating visual requirements -Often misses interactions between use cases Low-fidelity prototyping-Evaluating visual requirements -A little expensive -Need design skills Stakeholder review-Evaluating fit to context -Costs customer time Manual analysis-Checking for consistency -Easy to miss errors Formal analysis-Can guarantee formally specifiable properties -Expensive -Need formal skills Validation: Is your goal correct? Verification: Is your solution correct?

4 They probably know much more about the problem than you do. They probably have some ideas about how to solve the problem. They are your best resource for discovering your own mistakes before you start to code. Customers and users should be your friends

5 Abstraction Modularity: dividing into components. Information hiding Functional dependency Refinement Refactoring We will have another design gallery next week after making changes : including these factors. Fundamental design concepts that you need to keep in mind

6 Complete and sufficient Primitiveness: one service per class (one way of accomplishing the service not many ways) High cohesion: a cohesive design has a small focused set of responsibilities and single mindedly applies attributes and methods to implement those responsibilities. Low coupling: design classes within a subsystem should have only limited knowledge of other classes. Object oriented design concepts

7 Prototyping – Depict a design based on requirements, test if people can use it Stakeholder review – Present diagrams to customer & engineers, get feedback Analysis – Manually or automatically check properties of your requirements and design Approaches for evaluating requirements

8 Who are Stakeholders? Customers Users Domain experts Marketing specialists Lawyers or auditors Software engineers

9 1.Sit down with stakeholders 2.Engineers present their understanding of requirements 3.Stakeholders correct this understanding 4.Everybody discusses/argues/negotiates 5.Engineers revise requirements Repeat, if necessary. Stakeholder review

10 Make sure that all of the “right” people attend – In advance, ask stakeholders if they know of other people who need to attend – Consciously consider having user representatives attend the meeting But try to keep the attendee list <= 8 people – So that everybody at the meeting can be heard – So that you don’t waste $$$$  People should attend if and only if their attendance would be valuable. 1. Sit down with stakeholders

11 The situation of the customers / users Key problems faced by customers / users Key use cases to be supported by system – Often helpful to present diagrams from the requirements definition Visualizations of possible system interface – Often helpful to present low-fidelity prototypes Make it clear that you welcome feedback. 2. Engineers present their understanding of the requirements

12 Your customer / users / other stakeholders will probably interrupt the designers If your stakeholder says something that you don’t understand, try to get him/her to explain in terms of a concrete scenario. – More details later It’s often helpful have a note-taker responsible for recording customer feedback. 3. Stakeholders correct this understanding

13 Focus on concrete scenarios – A specific example of how a particular person would use the system in a certain real-world situation – An instance of a use case – Scenarios will support system testing later. Discussion is how you make sure that your requirements are correct, unambiguous, and testable. 4. Everybody discusses requirements

14 Focus on risk management – What scenarios might be hard to support? – What scenarios are impossible to support? – What requirements contradict one another? Arguing is particularly necessary when requirements contradict one another. 4. Everybody argues about requirements

15 Focus on prioritization, rather than eliminating support for scenarios – I only have so much time; what should I do first? – That way, reqs can be complete yet affordable. Watch for opportunities to use incremental or iterative development processes – Incremental: is there a part that we can build really well right now, then add more parts later? – Iterative: can we do a low-quality version of the entire system, then improve it later? 4. Everybody negotiates about requirements

16 Update the requirements definition and specification based on the review’s results. Every single requirement should have been reviewed with stakeholders at least once. – Keep track of what scenarios and comments came from stakeholders for each requirement – Helps to ensure relevance and traceability 5. Engineers revise requirements.

17 1.Sit down with stakeholders 2.Engineers present their understanding of requirements – The situation of the customers / users – Key problems faced by customers / users – Key use cases to be supported by system -> – Visualizations of possible system interface -> 3.Stakeholders correct this understanding 4.Everybody discusses/argues/negotiates 5.Engineers revise requirements Stakeholder review

18 Actor: Homeowner or business worker Precondition: Monitors have been sending information to website for a while Postcondition: User can see energy usage as well as tips for reducing usage Flow of events: – User logs into website – Website shows configurable charts showing usage – Website offers tips based on energy consumption, outlet info and external data (e.g. other user data) UC#1: Review online data

19 Possible user interface for reviewing online

20 Prototyping – Depict a design based on requirements, test if people can use it Stakeholder review – Present diagrams to customer & engineers, get feedback Analysis – Manually or automatically check properties of your requirements and design Approaches for evaluating requirements

21 1.Sit down with stakeholders 2.Engineers present their understanding of requirements 3.Stakeholders correct this understanding 4.Everybody discusses/argues/negotiates – Explain using scenarios – Identify risks – Use incremental or iterative development? 5.Engineers revise requirements Stakeholder review

22 Systematically check consistency between requirements definition and specification – If you “execute” or “simulate” the use cases, would the system suffice? – If the definition says that the system has feature X, does the specification indicate how to support X? Manual analysis

23 1.Define two formal models – Describing the requirement definition – Describing the requirement specification 2.Automatically check if the specification satisfies the definition Details on formal analysis

24 Good requirements are… Correct: They have to say the right things. Consistent : They can’t contradict each other. Unambiguous: Each must have 1 interpretation. Complete: They cover all the important stuff. Relevant: Each must meet a customer need. Testable: There must be a way to tell if they are satisfied. Traceable: There must be a way to determine their origin.

25 Get together in your project groups Do your set of functional requirements satisfy these, how and why? You could also include this as part of your report. In-class activity sheet 10min

26 Good requirements are… Correct: They have to say the right things. Consistent : They can’t contradict each other. Unambiguous: Each must have 1 interpretation. Complete: They cover all the important stuff. Relevant: Each must meet a customer need. Testable: There must be a way to tell if they are satisfied. Traceable: There must be a way to determine their origin.

27 Is each requirement consistent with the overall objective? Do some requirements provide a level of technical detail that is inappropriate at this stage? Is the requirement really necessary or does it represent an add-on feature that may not be essential to the objective of the system? Is each requirement bounded and unambiguous? Validating requirements 10min

28 Do any requirements conflict with other requirements? Is each requirement testable once implemented? Does the requirement model properly reflect the information function and behavior of the system to be built? Have ALL the requirements been validated with customer requirements? Validating requirements 10min

29 Prototyping – Depict a design based on requirements, test if people can use it Stakeholder review – Present diagrams to customer & engineers, get feedback Analysis – Manually or automatically check properties of your requirements and design Approaches for evaluating requirements

30 One of you play the role of lead system designer. 1 person is a note taker 1 or 2 customer(s) : based on the feedback you can choose. Based on the prototypes that you all had seen and the critiques/appreciation received prioritize them and discuss about what decision need to be taken. Example: Prototyping a system stakeholder review 15min

31 Prototyping with the customer: one day Tomorrow/Thursday? Prototyping with customer

32 – Validating requirements definition: do you thoroughly understand the customer’s problem? – Verifying requirements specification: have you thoroughly checked that your solution will solve the problem? Prototyping with customer


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