7. Requirements

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7. Requirements
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Requirements?

• Describes what the system should do
• Its services and constraints
• A high-level specification of whats expected of
  the system
• It should not dictate how the system should be
  implemented, however

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Types of Specification

• User requirements
• System requirements
• Functional spec
• Design specification
• Adds more details and constraints to system
  requirements

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Who is it intended for?

• User Requirements
• Managers, end users, developers, architects
• System requirements
• End users, developers, architects
• Design Specification
• Developers, architects

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Types of Requirements

• Functional
• Behavior and interaction of the system
• What it is supposed to do
• Non-functional
• Constraints on the services
• Performance, concurrency, standards, etc.
• Domain
• Domain specific constraints
• May be functional or non-functional

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Functional requirements

• Specifies the interaction with the system
• Detailed list of what can be done using the
  application
• Users may not be very specific though expected to
  be precise
• Developers often misinterpret
• Requirements often change or are modified
  leading to increased cost

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Non-functional Requirements

• Stem from constraints, not from specifications
• System related constraints
• Reliability, speed, performance, concurrency,
  storage requirements, interface restrictions,
• Generally at the system specification level and
  are mostly critical has wide effect on the
  systems success

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Non-functional Requirements

• Some of these may not be related to application,
  but related to process
• Requirements on how the system is developed,
  documented, progress is monitored, etc.
• consider a application that requires FDA
  approval!

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Type of non-functional reqs.

• Product requirements
• Usability
• Efficiency Performance, space, Concurrency
• Reliability
• Portability
• Organizational requirements
• Delivery, implementation, standards
• External requirements
• Interoperability, ethical, legislative, privacy,
  safety

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Risks from non-functional reqs

• Some of these are hard to verify
• Need to test often to make sure system meets
  these
• Nice if quantitative metrics can be created to
  measure these