Metrics
Traditional
Object-Oriented
Fan-in/fan-out
Weighted methods per class
Lines of code
Cyclomatic complexity*
Comment percentage
Length of identifiers
Response for a class
Lack of cohesion of methods*
Coupling between objects*
Depth of inheritance tree
Depth of conditional nesting
Fog index
Number of children
Number of overriding operations
* November 2002
see http://satc.gsfc.nasa.gov/support/STC_APR98/apply_oo/apply_oo.doc
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Traditional Metrics
Fan-in/fan-out
Fan-in is a measure of the number
of functions that call some other
function, say X
Fan-out is a measure of the
number of functions which are
called by a function, say X.
(See RFC)
Cyclomatic
complexity
Nov 2002
CC is a count of the number of test
cases required to test comprehensively
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Traditional Metrics
Lines of Code
LOC can be counted as
•lines (LOC)
•non-comment non-blank lines
(NCNB)
•executable statements (EXEC)
Note that NASA uses executable
lines of code to evaluate size
Comment
percentage
Nov 2002
Calculated as the total number of
comments divided by the {total
lines of code less the number of
blank lines}
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Traditional Metrics
Depth of
conditional
nesting
Measure of the depth of nesting of
IF statements in programs
Length of
identifiers
Measures average length of
distinct identifiers
Fog index
Measure of the average length of
words and sentences in documents.
The higher the value for the Fog
index, the more difficult ...
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OO Metrics
Weighted
methods per
class
WMC is the number of methods
included in a class weighted by the
complexity of each method
Response for a
class
RFC is a count of all methods that
can be invoked in response to a
message to an object of the class
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OO Metrics
Lack of cohesion
of methods
LOCM measures the dissimilarity
of methods in a class. A highly
cohesive module stands alone.
Lack of cohesion increases
complexity.
Coupling
between objects
CBO is a count of the number of
other classes to which a class is
coupled. Measured by counting the
number of distinct non-inheritance
related class hierarchies on which
a class depends
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OO Metrics
Depth of
inheritance tree
DIT is the maximum number of
steps from the class node to the
root of the tree
Number of
children
NOC is the number of immediate
subclasses subordinate to a class in
the hierarchy
Number of
overriding
operations
Number of operations in a
superclass that are overridden in a
subclass
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WMC
Weighted
methods per
class
WMC is the number of methods
included in a class weighted by the
complexity of each method
How does one count this?
a) simply count the number of methods, or,
b) sum the complexities of the methods (complexity might be
rated: 1 Simple, 2 Moderately complex, 3 Complex)
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WMC
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RFC
Response for a
class
RFC is a count of all methods that
can be invoked in response to a
message to an object of the class
How does one count this?
For a class, we count the number of distinct methods that can
be invoked in response to a message, including all methods
within the class hierarchy
For a class, we count all messages that can be sent by all
methods in the class
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RFC
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LCOM
Lack of cohesion
of methods
LOCM measures the dissimilarity
of methods in a class. A highly
cohesive module stands alone.
Lack of cohesion increases
complexity.
How does one count this?
We need a way of measuring cohesiveness (or not).
Possibilities:
a) compute the average over all attributes in a class
number of methods using the attribute
total number of methods
convert to a percentage and subtract from 100
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LCOM
Possibilities (continued):
b) for each method, create a set of the attributes it accesses.
For each pair of methods, perform the intersection of
attributes. If an intersection is not empty put the set in P; if it
is empty put the set in Q.
The measure is the difference in cardinalities of P and Q:
LCOM =
P -
Q
if
P >
Q
otherwise LCOM = 0
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LCOM
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CBO
Coupling
between objects
CBO is a count of the number of
other classes to which a class is
coupled. Measured by counting the
number of distinct non-inheritance
related class hierarchies on which
a class depends
How does one count this?
• count the number of distinct noninheritance-related class
hierarchies on which a class depends
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CBO
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DIT
Depth of
inheritance tree
Nov 2002
DIT is the maximum number of
steps from the class node to the
root of the tree
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NOC
Number of
children
NOC is the number of immediate
subclasses subordinate to a class in
the hierarchy
How does one count this?
• the number of immediate subclasses subordinate to a class in
the hierarchy
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NOC
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CC
Cyclomatic
complexity
CC is a count of the number of test
cases required to test comprehensively
CC measures the amount of decision logic in a module.
A value of 10 or less is the general recommendation.
Formally, based on a program’s flowgraph,
Cyclomatic complexity
= number of edges
– number of nodes
+2
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CC
Control flowgraphs describe the logic structure of software
modules.
• A module corresponds to a single function or subroutine in
typical languages, has a single entry and exit point, and is
able to be used as a design component via a call/return
mechanism.
Each flowgraph consists of nodes and edges.
• nodes represent computational statements or expressions,
• edges represent transfer of control between nodes.
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Flowgraph Construction - Sequence
x=z
y=7
CC=?
y=10
Sequences are reducible to a single node:
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Flowgraph Construction – If then
if x>4 then
y=7
…
CC=
end if
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Flowgraph Construction – If Else
if x>4 then
y=7
…
CC=
else
y=10
…
end if
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Flowgraph Construction - While
while x>0 do
x=x/2
…
CC=
end while
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Flowgraph Construction – Do Until
Do
…
Read x
CC=
Until x=0
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Program
FindMean (FILE ScoreFile)
{ float SumOfScores = 0.0;
int NumberOfScores = 0;
float Mean=0.0; float Score;
Read(ScoreFile, Score);
2 while (! EOF(ScoreFile) {
3 if (Score > 0.0 ) {
SumOfScores = SumOfScores + Score;
NumberOfScores++;
}
4
5
Read(ScoreFile, Score);
}
/* Compute the mean and print the result */
6 if (NumberOfScores > 0) {
Mean = SumOfScores / NumberOfScores;
printf(“ The mean score is %f\n”, Mean);
} else
printf (“No scores found in file\n”);
9 }
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8
27
Flowgraph
1
Cyclomatic
complexity
2
= CC
3
= 11-9+2 = 4
4
decision structures:
5
•one while
6
7
8
•one if then
•one if else
9
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CC
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