Addressing Non-functional Requirements in Software Architecture

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Addressing Non-functional Requirements in
Software Architecture

• By Dennis Bystritsky

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What are Non-functional Requirements (NFRs)?

• Specify criteria that can be used to judge the
  operation of a system, rather than specific
  behaviors
• Example Usability, dependability, security
  level, testability

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How to address NFRs in system architecture?

• Problematic
• Cant make a concrete module for something like
  testability
• Should be a quality of the system as a whole
• So can we even specify NFRs in early system
  architecture?

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Lets first understand NFRs

• NFRs are
• Operationalizable implemented through
  functional components for the entire architecture
  (such as security)
• Checkable system can include components which
  check that the desired quality is met (such as
  performance)

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Functional requirements and NFRs

• Must be considered differently
• Separation of concerns
• Architecture components for FRs might realize
  some NFRs
• We try to reduce tangling

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First step?

• Separate functional requirements from
  non-functional ones

• Login screen
• Progress bar
• Administrator access
• Help screen
• Authentication

• Security
• Performance
• Usability

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Next

• Implement system architecture based on functional
  requirements
• Should be relatively easy since each requirement
  links to one or more specific modules

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Finally

• For each NFR
• Link it to one or more architectural modules
• Feel free to create new modules as needed

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How do we link?

• XML binders
• Use XML-style language to specify how NFRs link
  to functional components of the architecture

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What we have done

• Separated FRs from NFRs
• Created system architecture which addresses both
  sets of requirements
• Reduced tangling

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Future Work

• Evaluation of software architecture
• How to determine which architectures address
  requirements better than others