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151 lines
4.9 KiB
Markdown
151 lines
4.9 KiB
Markdown
---
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sr-due: 2022-04-06
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sr-interval: 15
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sr-ease: 232
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---
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tags: #review
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resources:
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[article about requirements](https://sceweb.uhcl.edu/helm/RationalUnifiedProcess/process/workflow/requirem/co_req.htm#Reliability)
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[IBIS](https://en.wikipedia.org/wiki/Issue-based_information_system)
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[moscow method](https://en.wikipedia.org/wiki/MoSCoW_method)
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---
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## Review Questions
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1. Name three properties of good requirements and for each property explain why it is a good property. (NUUCCC)
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- understandable -> by users -> reduces misunderstandings
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- un-ambiguous -> reduces midunderstandings
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- complete -> nothing missing
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- non-prescriptive -> say what the system should do, not how it should do it
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- consistent => do not contradict each other
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- correct -> as judged by user
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2. What is the difference between functional and non-functional requirements?
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- features vs contraints
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3. What effects do poor quality requirements have on the subsequent development of the system?
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- increased cost/time
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- increase chance of failure
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- more difficult maintenance
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- not meeting needs of client
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4. How are requirements elicited and managed using the three main agile methodologies presented in the lectures?
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- scrum
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- requirements owned and priotitised by the product owner
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- XP
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- based on user stories, continuous involvement of users
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- UP
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- requirements contructed in at the beginning
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- functional req's implemented first then contrainst like security, performance etc
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___
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# Requirements
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> “…descriptions of how the system should behave, application domain information, constraints on the system’s operation, or specifications of a system property or attribute.” - Kotonya and Sommerville, 2001, p. 6
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> “…a statement of need, something that some class of user or other stakeholder wants.” - Alexander and Stevens, 2002, p. 8
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something the system should do or a contrainst the system should adhere to
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## Requirements engineering
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> “…to cover all of the activities involved in discovering, documenting, and maintaining a set of requirements for a computer-based system.” - Kotonya and Sommerville, 2001, p. 8
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robust way to develop requirements
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Key concepts
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- discovery -> capture, elicitation, identification
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- documenting -> specifying, modelling
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- maintenance -> manging changes in env of sys
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### Requirements document:
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- services and function
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- contraints
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- overall properties
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- systems env incl. related sys's
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- application domain information
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- constraints of development process
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## requirements in agile methodologies
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[[Agile Development#^e2bc0b|UP]]
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- Requirements (based on use cases) mostly elicited, modelled, and refined during inception, elaboration, and construction phases.
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- Functional requirements implemented before technical, performance, reliability requirements.
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[[Agile Development#^e9fd09|XP]]
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- Based on user stories rather than explicit individual requirements.
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- Continuous involvement of users who can make business decisions about functionality and scope.
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[[Agile Development#^4ddbdc|Scrum]]
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- user stories (if mapped back to business process to create stucture to the product backlog)
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- requirements owned and prioritised by the product owner
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## how to specify requirements
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published standards -> (e.g., ISO 9000, IEEE/ANSI 830-1993)
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natural language text desciptions and scenarios
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models
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- function catalogue
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- ERD's
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- UML's
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prototypes:
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- evolutionary -> changes to existing prototype/idea
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- revolutionary -> completely new
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formal mathematical notation
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## Good requirements
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^df23e2
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- understandable -> by users
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- non prescriptive -> what not how
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- correct -> as judged by user
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- complete -> nothing missing from _individual_ requirements
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-> nothing missing from _complete set_ of requirements
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- consistent -> do not contradict each toher
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- unambiguous -> one one possible interpretation
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- also
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- precise, concise, cohesive, feasible, relevant, up to date, testable, traceable
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## Type of requirements
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^c1a732
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### Functional requirements
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^9e1ad5
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what should the system do
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### Non-functional requirements
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^ab5ecd
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contraint -> how the system should do something
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e.g., behaviour , constrainst , usability , reliability , performance , security
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### FURPS
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usually overkill
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categories
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- functional -> features
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- usability -> UI and system availability
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- reliablility
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- performance
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- supportability
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furps + adds
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- design
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- implementation
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- interface
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- physical
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**examples**
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![[Pasted image 20220310162958.png|300]]
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## Consequences of poor requirements
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- Delays and extra costs
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- failure to meets real needs of customer
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- higher cost of maintenance
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- unreliable/non functional system
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## Causes of poor requirements
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- problem not well understood (domain comlpexity)
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- misunderstanding between parties
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- [[stakeholders]] -> not trained, dont have authority, are not available/plentiful
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- continually evolving requirements
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- requirements are -> incomplete/abmiguous/inconsistent/overlapping/unimplementable |