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Metrics

"A science is as mature

as its measurement tools."

-- Louis Pasteur

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Starter Quest ions

What can we measure?

What value can those

numbers have?

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Why Measure?

accurate estimation

how productive are we

quality improvement

what do we do well

what do we do poorly

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Types of Metrics

Product Metrics

direct measures - number of bugs, LOC

indirect measures - usability, maintainability

Project and Process Metrics

direct measures - costs, LOC per month

indirect measures - quality assurance, reliability

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Code Metrics

Size Lines of Code

Function Points

Efficiency BigO

Complexity Cyclomatic Complexity Halstead's complexity metrics (next slide)

Maintainability

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Halstead's Complexity Metrics

n1 = the number of distinct operators

n2 = the number of distinct operands

N1 = the total number of operators

N2 = the total number of operands

Program length N = N1 + N2

Program vocabulary n = n1 + n2

Volume V = N * (LOG2 n)Difficulty D = (n1 / 2) * (N2 / n2)

Effort E = D * V

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McCall's Quality Factors

Product Operations

Product

Revision

Product

Transition

Portability

Reusability

Interoperability

Maintainability

Flexibility

Testability

Correctness

Reliability

Efficiency

Integrity

Usability

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Operability

Training

Communicativeness

Input/Output volume

Input/Output gate

Access Control

Access Audit

Storage efficiency

Execution Efficiency

Traceability

Completeness

AccuracyError Tolerance

Consistency

Simplicity

Conciseness

Instrumentation

ExpandabilityGenerality

Self-Descriptiveness

Modularity

Machine Independence

Software System Independence

Communications Commonality

Data Commonality

Usability

Integrity

Efficiency

Correctness

Reliability

Maintainability

Testability

Flexibility

Reusability

Portability

Interoperability

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ISO 9126Quality Characteristics and Guidelines for Their Use

Quality Factors

1. Functionality

2. Reliability

3. Usability

4. Efficiency

5. Maintainability

6. Portability

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Design Metrics

Fan In

Fan Out

Morphology based on number of nodes, depth, width

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Module Design Metrics

Cohesion how many functions does a module perform

coincidental

logical - eg does all output temporal - eg all the startup work

procedural - executed in this order

communicational - module arrangement on work on what data

functional

Coupling how is the module connected to other modules

global variable, parameters, stands alone

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Object-Oriented Metrics

Weighted Methods per Class

not only how many methods per class are there, but also

how complex are they

Depth of Inheritance Tree

Number of Children

how many child classes does a class have

Response for Class number of local methods, plus number of methods they call

Lack of Cohesion Metric

number of non-intersecting (don't use the same variables)

methods

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Lack of Cohesion Example

Module A calls Module B

B accesses Variable X

C and D access Y

D calls E

This should be split into two classes.

A

B E

DC

XY

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Project Metrics

LOC or FP per month

Errors per LOC (aka Defect Density)

Defect Removal Efficiency

Time required to make changes

Test coverage

Required Skills

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Obviously,

Beware of Statistics

Version 2 Version 1Module# Defects LOC Defects/LOC Defects LOC Defects/LOC Relation

1 12 777 0.01544 3 55 0.05455