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ITIS 3310 Software Architecture and Design Chapter 15 Product Metrics for Software

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Title: ITIS 3310 Software Architecture and Design Chapter 15 Product Metrics for Software


1
ITIS 3310 Software Architecture and Design
Chapter 15 Product Metrics for Software
2
Software Quality
  • How do we define quality?
  • Conformance to
  • Explicitly stated functional and performance
    requirements
  • Explicitly documented development standards
  • Implicit characteristics that are expected of
    all professionally developed software

3
Software Quality
  • Mix of factors
  • Varies for
  • Different applications
  • Different customers
  • Three important points
  • Requirements are the foundation of quality
  • Standards need to be specified
  • Implicit requirements are often as important as
    explicit ones

4
Engine Analogy
  • 3 base qualities
  • Durability
  • Economy of operation
  • Power output
  • Emphasize one at the expense of the others
  • Optimize two at the loss of the third
  • Example Power
  • Power Economy Durability (longevity)
  • Family car 200 hp, 25 mpg, 200,000 mi.
  • NASCAR Cup 850 hp, 3-4 mpg, 600 miles
  • NHRA Top Fuel 6000 hp, 5 gal per ¼ mile ¼
    mi

5
McCalls Triangle of Quality
  • Measurement of software quality can be
  • Direct
  • Defects uncovered during testing
  • Performance
  • Indirect
  • Usability
  • Maintainability
  • In either case, measurement is important!
  • Compare a metric to some goal

6
McCalls Triangle of Quality
  • McCall, Richards, Walters categorization of
    software quality factors
  • Product operation
  • Operational characteristics
  • Product revision
  • Ability to undergo change
  • Product transition
  • Adaptability to new environments

7
McCalls Triangle of Quality
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McCalls Triangle of Quality
  • Correctness
  • Satisfies expectations
  • Fulfills customers mission objectives
  • Reliability
  • Expectation of performing intended function with
    required precision
  • Efficiency
  • Consumption of resources to deliver functionality

9
McCalls Triangle of Quality
  • Integrity
  • Access/control by unauthorized persons can be
    controlled
  • Usability
  • Effort required to learn, operate, prepare input
    for, and interpret output of
  • Maintainability
  • Effort required to locate and fix an error

10
McCalls Triangle of Quality
  • Flexibility
  • Effort required to modify
  • Testability
  • Effort required to test for intended
    functionality
  • Portability
  • Effort required to transfer operations to a
    different hardware platform or operating system
    environment

11
McCalls Triangle of Quality
  • Reusability
  • Extent to which parts of a system can be reused
    by other systems
  • Interoperability
  • Effort necessary to connect two systems together

12
McCalls Triangle of Quality
  • Can these be measured directly?
  • Yes, if there is a single countable value
  • Size of a program in bytes
  • Transactions per second
  • Some can only be measured indirectly
  • Subjective assessment
  • Effort required to learn how to operate a program
  • Some may catch on quickly
  • Some may require extensive instruction and
    practice
  • Some many never get it

13
A Comment
McCalls quality factors were proposed in
the early 1970s. They are as valid today as they
were in that time. Its likely that software
built to conform to these factors will exhibit
high quality well into the 21st century, even if
there are dramatic changes in technology.
14
Resume 4/9
15
ISO 9216 Quality Factors
  • Functionality How the software satisfies stated
    needs
  • Suitability
  • Accuracy
  • Interoperability
  • Compliance
  • Security
  • Reliability Amount of time system is available
    for use
  • Maturity
  • Faulty tolerance
  • Recoverability

16
ISO 9216 Quality Factors
  • Usability Ease of use
  • Understandability
  • Learnability
  • Operability
  • Efficiency Optimum use of system resources
  • Time behavior
  • Resource behavior

17
ISO 9216 Quality Factors
  • Maintainability Ease of repair
  • Analyzability
  • Changeability
  • Stability
  • Portability Ease of transposition to new
    environment
  • Adaptability
  • Installability
  • Conformance
  • Replaceability

18
Measures, Metrics and Indicators
  • Major problem in measurement subjectivity
  • What is needed is a set of metrics
  • Applicable to quantitative assessment of software
    quality
  • Metrics necessarily represent indirect measure
  • What is the unit of measure for quality?
  • We can never directly measure quality
  • Instead, we measure some manifestation of quality
  • What counts is the precise relationship between
    the variable measured and the presumed quality of
    the software

19
Measures, Metrics and Indicators
  • A measure provides a quantitative indication of
    the extent, amount, dimension, capacity, or size
    of some attribute of a product or process
  • The IEEE glossary defines a metric as a
    quantitative measure of the degree to which a
    system, component, or process possesses a given
    attribute.
  • An indicator is a metric or combination of
    metrics that provide insight into the software
    process, a software project, or the product
    itself

20
Measures, Metrics and Indicators
  • We

Collect measures in order to
Develop metrics that
Reveal indicators of quality
21
Measurement Principles
  • The objectives of measurement should be
    established before data collection begins
  • Each technical metric should be defined in an
    unambiguous manner
  • Metrics should be based on a theory that is valid
    for the domain of application (e.g., metrics for
    design should draw upon basic design concepts and
    principles)
  • Metrics should be tailored to best accommodate
    specific products and processes

22
Measurement Process
  • Formulation. The derivation of software measures
    and metrics appropriate for the representation of
    the software that is being considered
  • Collection. The mechanism used to accumulate data
    required to derive the formulated metrics
  • Analysis. The computation of metrics and the
    application of mathematical tools

23
Measurement Process
  • Interpretation. The evaluation of metrics results
    in an effort to gain insight into the quality of
    the representation
  • Feedback. Recommendations derived from the
    interpretation of product metrics transmitted to
    the software team

24
Goal-Oriented Software Measurement
  • The Goal/Question/Metric Paradigm
  • Technique for identifying meaningful metrics for
    any part of software process
  • Steps
  • Establish an explicit measurement goal that is
    specific to the process activity or product
    characteristic that is to be assessed
  • Define a set of questions that must be answered
    in order to achieve the goal, and
  • Identify well-formulated metrics that help to
    answer these questions.

25
Goal-Oriented Software Measurement
  • Goal definition template
  • Analyze the name of activity or attribute to be
    measured
  • for the purpose of the overall objective of the
    analysis
  • with respect to the aspect of the activity or
    attribute that is considered
  • from the viewpoint of the people who have an
    interest in the measurement
  • in the context of the environment in which the
    measurement takes place.

26
Goal-Oriented Software Measurement
  • Analyze the SafeHome software architecture for
    the purpose of evaluating architectural
    components with respect to the ability to make
    SafeHome more extensible from the viewpoint of
    the software engineers performing the work in the
    context of product enhancement over the next
    three years.

27
Goal-Oriented Software Measurement
  • Now develop questions

Are architectural components characterized in a
manner that compartmentalizes function and
related data?
Is the complexity of each component within bounds
that will facilitate modification and extension?
  • Now identify metrics that answer each question
    quantitatively

28
Metrics Attributes
  • Simple and computable
  • Relatively easy to learn how to derive the metric
  • Its computation should not demand inordinate
    effort or time
  • Empirically and intuitively persuasive
  • Should satisfy an intuitive notion about the
    product attribute under consideration
  • Consistent and objective
  • Should always yield results that are
  • The same from measurement to measurement
  • Unambiguous

29
Metrics Attributes
  • Consistent in its use of units and dimensions
  • The mathematical computation of the metric should
    use measures that do not lead to bizarre
    combinations of unit
  • Programming language independent
  • Metrics should be based on the analysis model,
    the design model, or the structure of the program
    itself
  • An effective mechanism for quality feedback
  • The metric should provide a software engineer
    with information that can lead to a higher
    quality end product

30
Collection and Analysis Principles
  • Whenever possible, data collection and analysis
    should be automated
  • Valid statistical techniques should be applied to
    establish relationship between internal product
    attributes and external quality characteristics
  • Interpretative guidelines and recommendations
    should be established for each metric

31
Analysis Metrics
  • Function-based metrics
  • Use the function point as a normalizing factor or
    as a measure of the size of the specification
  • Specification metrics
  • Used as an indication of quality by measuring
    number of requirements by type

32
Function-Based Metrics
  • The function point metric (FP)
  • Can be used effectively as a means for measuring
    the functionality delivered by a system
  • Function points are derived using
  • An empirical relationship based on countable
    (direct) measures of software's information
    domain
  • Assessments of software complexity

33
Function-Based Metrics
  • Information domain values are defined in the
    following manner
  • Number of external inputs (EIs)
  • Number of external outputs (EOs)
  • Number of external inquiries (EQs)
  • Number of internal logical files (ILFs)
  • Number of external interface files (EIFs)

34
Function Points
35
Architectural Design Metrics
  • Architectural design metrics
  • Structural complexity g(fan-out)
  • Data complexity f(input output variables,
    fan-out)
  • System complexity h(structural data
    complexity)
  • HK metric architectural complexity as a function
    of fan-in and fan-out
  • Morphology metrics a function of the number of
    modules and the number of interfaces between
    modules

36
Metrics for OO Design-I
  • Size
  • Size is defined in terms of four views
    population, volume, length, and functionality
  • Complexity
  • How classes of an OO design are interrelated to
    one another
  • Coupling
  • The physical connections between elements of the
    OO design
  • Sufficiency
  • The properties of a class that make it useful for
    a purpose
  • Completeness
  • A measure of the properties required to fully
    represent a problem domain object

37
Metrics for OO Design-II
  • Cohesion
  • The degree to which all operations working
    together to achieve a single, well-defined
    purpose
  • Primitiveness
  • Applied to both operations and classes, the
    degree to which an operation is atomic
  • Similarity
  • The degree to which two or more classes are
    similar in terms of their structure, function,
    behavior, or purpose
  • Volatility
  • Measures the likelihood that a change will occur

38
Distinguishing Characteristics
Berard argues that the following characteristics
require that special OO metrics be developed
  • Localizationthe way in which information is
    concentrated in a program
  • Encapsulationthe packaging of data and
    processing
  • Information hidingthe way in which information
    about operational details is hidden by a secure
    interface
  • Inheritancethe manner in which the
    responsibilities of one class are propagated to
    another
  • Abstractionthe mechanism that allows a design to
    focus on essential details

39
Class-Oriented Metrics
Proposed by Chidamber and Kemerer
  • Weighted methods per class
  • Depth of the inheritance tree
  • Number of children
  • Coupling between object classes
  • Response for a class
  • Lack of cohesion in methods

40
Class-Oriented Metrics
Proposed by Lorenz and Kidd LOR94
  • Class size
  • Number of operations overridden by a subclass
  • Number of operations added by a subclass
  • Specialization index

41
Class-Oriented Metrics
The MOOD Metrics Suite
  • Method inheritance factor
  • Coupling factor
  • Polymorphism factor

42
Operation-Oriented Metrics
Proposed by Lorenz and Kidd LOR94
  • Average operation size
  • Operation complexity
  • Average number of parameters per operation

43
Component-Level Design Metrics
  • Cohesion metrics a function of data objects and
    the locus of their definition
  • Coupling metrics a function of input and output
    parameters, global variables, and modules called
  • Complexity metrics hundreds have been proposed
    (e.g., cyclomatic complexity)

44
Interface Design Metrics
  • Layout appropriateness
  • A function of
  • Layout entities
  • Their geographic position
  • The cost of making transitions among entities

45
Code Metrics
  • Halsteads Software Science a comprehensive
    collection of metrics all predicated on the
    number (count and occurrence) of operators and
    operands within a component or program
  • It should be noted that Halsteads laws have
    generated substantial controversy, and many
    believe that the underlying theory has flaws.
    However, experimental verification for selected
    programming languages has been performed (e.g.
    FEL89).

46
Metrics for Testing
  • Testing effort can also be estimated using
    metrics derived from Halstead measures
  • Binder BIN94 suggests a broad array of design
    metrics that have a direct influence on the
    testability of an OO system.
  • Lack of cohesion in methods (LCOM).
  • Percent public and protected (PAP).
  • Public access to data members (PAD).
  • Number of root classes (NOR).
  • Fan-in (FIN).
  • Number of children (NOC) and depth of the
    inheritance tree (DIT).

47
Summary
  • Metrics for software is still in its infancy
  • Different fields also have different maturity
  • OO techniques still immature
  • Testing and Maintenance immature
  • Many of the methods are hotly debated
  • Field will mature
  • Start now with some easily defined and measured
    aspects
  • OVERALL use metrics as a tool, not a weapon!
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