Software Engineering Product Metrics for Software

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• In a general sense, software quality is
• Conformance to explicitly stated functional and
  performance requirements, explicitly documented
  development standards, and implicit
  characteristics that are expected of all
  professionally developed software.
• There are three key points
• Software requirements are the foundation from
  which quality is measured. Lack of conformance to
  requirements is a lack of quality.
• Specified standards define a set of development
  criteria that guide the manner in which software
  is engineered. If the criteria are not followed,
  lack of quality will almost surely result.
• There is a set of implicit requirements that
  often goes unmentioned (e.g. the desire for ease
  of use). If software conforms to its explicit
  requirements but fails to meet implicit
  requirements, software quality is suspect.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• McCalls Quality Factors
• Factors that affect software quality can be
  categorized in two broad groups
• Factors that can be directly measured (e.g.
  defects uncovered during testing)
• Factors that can be measured only indirectly
  (e.g. usability or maintainability)

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• McCalls Quality Factors
• Correctness The extent to which a program
  satisfies the specification and fulfills the
  customers mission objectives.
• Reliability The extent to which a program can be
  expected to perform its intended function with
  required precision.
• Efficiency The amount of computing recourses and
  code required by a program to perform its
  function.
• Integrity The extend to which access to software
  or data by unauthorized persons can be
  controlled.
• Usability The effort required to learn, operate,
  prepare input for and interpret output of a
  program. (This can be contradictory, can any
  guess why?)

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• McCalls Quality Factors
• Usability The effort required to learn, operate,
  prepare input for and interpret output of a
  program. (This can be contradictory, can any
  guess why?)
• What is efficient for a power user may not be
  effective for a end or novice user.
• Maintainability The effort required to locate
  and fix an error in a program.
• Flexibility The effort required to modify an
  operational program.
• Testability The effort required to test a
  program to ensure that it performs the intended
  function.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• McCalls Quality Factors
• Portability The effort required to transfer the
  program from one hardware and/or software system
  environment to another.
• Reusability The extent to which a program or
  parts of a program can be reused in other
  applications related to the packaging and scope
  of the functions that the program performs
• Interoperability The effort required to couple
  one system to another.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• McCalls Quality Factors
• It is difficult, and in some cases impossible to
  develop direct measures of these quality factors.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• ISO 9126 Quality Factors
• A standard developed in an attempt to identify
  attributes for computer software.
• Functionality The degree to which the software
  satisfies stated needs as indicated by the
  following sub-attributes suitability, accuracy,
  interoperability, compliance, and security.
• Reliability The amount of time that the software
  is available for use as indicated by the
  following sub-attributes maturity, fault
  tolerance, recoverability.
• Usability The degree to which the software is
  easy to use as indicated by the following
  sub-attributes understandability, learnability,
  operability.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• ISO 9126 Quality Factors
• Efficiency The degree to which the software
  makes optimal use of system resources as
  indicated by the following sub-attributes time
  behavior, resource behavior.
• Maintainability The ease with which repair may
  be made to the software as indicated by the
  following sub-attributes analyzability,
  changeability, stability, and testability.
• Portability The ease with which the software can
  be transposed from one environment to another as
  indicated by the following sub-attributes
  adaptability, installability, conformance, and
  replaceability.
• Again these factors do not necessarily lend
  themselves to direct measurement.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• Transition to a Quantitative View
• Subjectivity and specialization apply to
  determining software quality.
• To help solve the problem, a more precise
  definition of software quality is needed as well
  as a way to derive quantitative measurements of
  software quality for objective analysis.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• Measure provides a quantitative indication of
  the extent, amount, dimension, capacity, or size
  of some attribute of a product or process.
• Measurement is the act of determining a measure.
• Metric relates the individual measure in some
  way (e.g. the average number of errors found per
  review or the average number of errors found per
  unit test)
• CHALLENGES OF PRODUCT METRICS
• Researchers have attempted to develop a single
  metric that provides a comprehensive measure of
  software complexity.
• It is fair to ask, just how valid product metrics
  are?

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• A metric should have desirable mathematical
  properties (i.e. a meaningful range, zero to
  one).
• When a metric represents a software
  characteristic that increase when positive traits
  occur or decreases when undesirable traits are
  encountered, the value of the metric should
  increase or decrease in the same manner.
• Each metric should be validated empirically in a
  wide variety of contexts before being published
  or used to make decisions.

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• Good attributes for software metrics are
• Simple and Computable
• Intuitively persuasive
• Consistent and objective
• Consistent in the use of units and dimensions
• Programming language independent
• An effective mechanism for high-quality
  feedback.

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Software Engineering Product Metrics for
Software

• METRIC FOR SOURCE CODE
• n1 the number of distinct operators that appear
  in a program
• n2 the number of distinct operands that appear
  in a program
• N1 the total number of operator occurrences.
• N2 the total number of operand occurrence.
• Overall program length N can be computed
• N n1 log2 n1 n2 log2 n2
• V N log2 (n1 n2)

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Software Engineering Product Metrics for
Software

• METRIC FOR TESTING
• n1 the number of distinct operators that appear
  in a program
• n2 the number of distinct operands that appear
  in a program
• N1 the total number of operator occurrences.
• N2 the total number of operand occurrence.
• Program Level and Effort
• PL 1/(n1 / 2) x (N2 / n2 l)
• e V/PL

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Software Engineering Product Metrics for
Software

• SOFTWARE QUALITY
• METRICS FOR MAINTENANCE
• Mt the number of modules in the current release
• Fc the number of modules in the current release
  that have been changed
• Fa the number of modules in the current release
  that have been added.
• Fd the number of modules from the preceding
  release that were deleted in the current release
• The Software Maturity Index, SMI, is defined as
• SMI Mt (Fc Fa Fd)/ Mt