march 25,200291.3913 r. mcfadyen1 metrics fan-in/fan-out lines of code cyclomatic complexity comment...
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March 25,2002 91.3913 R. McFadyen 1
Metrics
Fan-in/fan-out
Lines of code
Cyclomatic complexity
Comment percentage
Length of identifiers
Depth of conditional nesting
Fog index
Weighted methods per class
Response for a class
Lack of cohesion of methods
Coupling between objects
Depth of inheritance tree
Number of children
Number of overriding operations
Traditional Object-Oriented
Traditional metrics can be applied to OO environments too
see http://satc.gsfc.nasa.gov/support/STC_APR98/apply_oo/apply_oo.htm
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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
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
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
Fog index Measure of the average length of words and sentences in documents. The higher the value for the Fog index, the more difficult ...
Length of identifiers
Measures average length of distinct identifiers
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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
Shows that most classes
have less than 20
methods, … but some
have over 200 methods.
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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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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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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
A CBO value of zero
corresponds to a class
that is only coupled to
others in its
related
inheritance hierarchy
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DIT
Depth of inheritance tree
Most classes are at
level 0 and 1
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.
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Due in class April 3, 2002
4 questions:
For the code on pages 313-316,
1. Illustrate the complexity graph and determine the CC for getTotal()
2. Determine the WMC for Sale, SalesLineItem, and ProductSpecification
- use WMC technique a)
3. Determine the LCOM for ProductSpecification and SalesLineItem
- use LCOM technique a)
Assignment 4
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4. Based on Figures 20.11 and the code on pages 313-316, design an object to relational mapping for Sale, SalesLineItem, and ProductSpecification.
Illustrate the Sale, SalesLineItem, ProductSpecification rows that would exist given the test data at the bottom of Page 312.
Assignment 4
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