NASA OSMA SAS '03

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NASA OSMA SAS '03

• Use Case Quality Attributes
• James R. McCoy
• SRS Technologies
• Software Assurance Technology Center
• http//satc.gsfc.nasa.gov
• james.mccoy_at_gsfc.nasa.gov

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Overview

• Introduction to the UML Use Cases
• Research Initiative
• Validating Use Cases, Risk Indicators Use Case
  Metrics
• Requirements Use case Tool
• Summary

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Introduction

• System requirements are the foundation upon which
  an entire system is built
• Correct, complete testable requirements are
  critical success of a project is directly
  affected by the quality of requirements
• Traditional vehicle for capturing communicating
  requirements is the Software Requirements
  Specification (SRS)
• Use cases provide a more user-centered approach
  for specifying requirements

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Unified Modeling Language

• The Unified Modeling Language (UML) is the
  industry-standard language for specifying,
  visualizing, constructing documenting artifacts
  of complex software systems
• The UML
• Is a language
• Applies to modeling and systems
• Is based on the object-oriented paradigm

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Use Cases

• At the heart of the UML are use cases
• The use case diagram is the driver for the eight
  remaining diagrams that compose the UML
• Use cases form the basis of how the system
  interacts with the outside world (users, other
  systems, etc.)

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Use Case Model

• Use cases were designed to capture, via a
  combination of structured text graphics, the
  functional requirements of a system
• Use cases are usually described in a textual
  document that accompanies a use case diagram the
  combination of these use case diagrams their
  supporting documentation is known as a use case
  model

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Use Case Model

• Use case models
• Illustrate a systems intended functions (use
  cases), its surroundings (actors) the
  relationships between them (use case diagrams)
• Are used to communicate
• Provide a vehicle used by customers developers
  to discuss the systems functionality

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UML Use Case Diagram

• Fowler, M., Scott, K., UML Distilled Applying
  the Standard Object Modeling Language,
  Addison-Wesley, 1997.

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Research Initiative

• Extensive research has been conducted on
  expressing software requirements in natural
  language has resulted in the development of a
  tool for evaluating them
• Initiative is to enhance refine a use case tool
  that provides a more methodological basis for
  specifying managing understandable, buildable
  verifiable functional requirementsespecially for
  large, object-oriented projects

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Research Goals

• Identify the attributes of quality use cases
• Level of validity
• Risk indicators
• Metrics
• Develop software tool for analyzing use cases
  based on these characteristics

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Validating Use Cases

• Is the use case complete?
• Is the actors goal going to be met?
• Are there any changes that would simplify the
  process depicted in the use case?
• Are there any additional goals that are not
  addressed?
• Are there any additional actors that are not
  represented?

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Risk Indicators

• Options give the developer latitude in satisfying
  the specification statements that contain them.

• Can
• May
• Optionally

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Risk Indicators

• Incompletes provide a basis for expanding a
  requirement or adding future requirements.

• TBD
• TBS
• TBE
• TBC
• TBR

• Not defined
• Not determined
• But not limited to
• As a minimum

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Risk Indicators

• Weak phrases are clauses that are apt to cause
  uncertainty and leave room for multiple
  interpretations.

• Adequate
• As appropriate
• Be able to
• Be capable of
• Capability of
• Capability to

• Effective
• As required
• Normal
• Provided for
• Timely
• Easy to

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Use Case Metrics

• Ambiguity Weak Phrases Options
• Completeness Incompletes
• Volatility Changes / Requirements
• Traceability Use Cases Traced to Test Cases

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Requirements Use case Tool

• The Requirements Use case Tool (RUT) provides
  assistance to managers, customers developers in
  assessing the quality of use cases
• In addition, RUT serves as a database repository
  for requirements developed as use cases
• RUT is a valuable resource for collecting,
  evaluating maintaining software requirements
  gathered as use cases

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RUT Features

• Web-based multi-user
• Open source multi-platform
• Use case repository
• Standard use case template
• Integration with Rational Rose
• Configuration management
• Risk analysis
• Metrics
• Test case generation traceability

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Summary

• Extensive research has been conducted on writing
  quality software requirements in a natural
  language, resulting in guidelines for writing
  effective requirements a tool for evaluating
  them
• Current software development practices provide a
  more methodological basis for specifying
  managing quality requirements
• The goal of the Requirements Use case Tool is to
  provide a clear evaluation technique for software
  requirements written as use cases
• Future work is needed to introduce this tool to
  NASA projects