1. March 25,200291.3913 R. McFadyen1 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 TraditionalObject-Oriented Traditional metrics can be applied to OO environments too see http://satc.gsfc.nasa.gov/support/STC_APR98/apply_oo/apply_oo.htm

2. March 25,200291.3913 R. McFadyen2 Traditional Metrics Fan-in/fan-outFan-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

3. March 25,200291.3913 R. McFadyen3 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}

4. March 25,200291.3913 R. McFadyen4 Traditional Metrics Depth of conditional nesting Measure of the depth of nesting of IF statements in programs Fog indexMeasure 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

5. March 25,200291.3913 R. McFadyen5 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

6. March 25,200291.3913 R. McFadyen6 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

7. March 25,200291.3913 R. McFadyen7 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

8. March 25,200291.3913 R. McFadyen8 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)

9. March 25,200291.3913 R. McFadyen9 WMC Shows that most classes have less than 20 methods, … but some have over 200 methods.

10. March 25,200291.3913 R. McFadyen10 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

11. March 25,200291.3913 R. McFadyen11 RFC In this case, about half the classes have an RFC <=20

12. March 25,200291.3913 R. McFadyen12 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

13. March 25,200291.3913 R. McFadyen13 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 - Qif P > Q otherwise LCOM = 0

14. March 25,200291.3913 R. McFadyen14 LCOM

15. March 25,200291.3913 R. McFadyen15 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

16. March 25,200291.3913 R. McFadyen16 CBO A CBO value of zero corresponds to a class that is only coupled to others in its related inheritance hierarchy

17. March 25,200291.3913 R. McFadyen17 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

18. March 25,200291.3913 R. McFadyen18 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

19. March 25,200291.3913 R. McFadyen19 NOC One of these classes, at depth 3, has almost 40 children!

20. March 25,200291.3913 R. McFadyen20 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.

21. March 25,200291.3913 R. McFadyen21 CC

22. March 25,200291.3913 R. McFadyen22 CC

23. March 25,200291.3913 R. McFadyen23 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

24. March 25,200291.3913 R. McFadyen24 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