The CK Metrics Suite

1
The CK Metrics Suite
2
Weighted Methods Per Class

• To use this metric, the software engineer must
  repeat this process n times, where n is the
  number of methods for the given class. In order
  to complete this process, the software engineer
  must do the following,
• Compute the complexity of the method, using a
  specific complexity measure. Please see links for
  more information on complexity metrics.
• Input the value into the text box.
• Click the Add button.
• Continue process until all methods have been
  completed.

3
Depth of Inheritance Tree

• In order to calculate this metric, the Software
  Engineer must consult their Inheritance tree.
• An Example of this is as follows,
• To find this, the Software Engineer must traverse
  the tree until the deepest child has been
  visited. It is then this number that should be
  entered.
• In the preceding example, the number to be
  entered into the cell would be 4.

4
Number of Children

• In order to calculate this metric, the Software
  Engineer must consult their Inheritance Tree.
• An Example of this is as follows,
• To calculate this metric, the Software Engineer
  must calculate the number of children that are
  one level below the class under calculation.
• In the preceding example, the number of children
  for C2 is 3 (C21, C22, C23).

5
Coupling between Object Classes

• In order to find the coupling between object
  classes, the Software Engineer must consult
  his/her set of CRC cards.
• To find this value, the Software Engineer must do
  the following,
• Obtain the class under calculation CRC index
  card.
• Count the number of collaborations listed for the
  class.
• Input this number into the cell.

6
Response for a Class

• In order to calculate responce for a class, the
  Software Engineer must do the following,
• Consult the classes CRC index card.
• Take the first message and count the number of
  methods that can potentially be executed in
  response to this message
• Record this number, and repeat this process for
  all methods.
• When finished, input the greatest number into the
  cell.

7
Lack of Cohesion in Methods

• In order to calculate the lack of Cohesion in
  methods, the Software Engineer must consult their
  CRC index cards. They should then do the
  following,
• Pick the first attribute.
• Go through the list of CRC cards and count the
  number of cards that access that particular
  attribute picked in step one.
• Record this number and repeat until all
  attributes have been processed.
• Take the greatest number and input this number
  into the cell.

8
Example of CK Metrics

• For the first box enter 0.76 , 0.76, 0.79 the
  hit ok after each one.
• For the remaining boxes enter 5
• Formula for calculations
• WMC S Ci
• Weighted Metrics Class Sum Classes

9
CK Metrics Summary

• Weighted Methods Per Class (WMC) 0.77
• Depth of Inheritance Tree (DIT) 5
• Number of Children (NOC) 5
• Coupling between Object Classes (CBO) 5
• Response for a Class (RFC) 5
• Lack of Cohesion in Methods (LCOM) 5

10
CK Metrics Suggestions

• 1. Your Weighted Methods Per Class Metric is high
  thus limiting the potential reuse of this class.
• Therefore, you may want to reduce the number of
  methods and/or their complexity
• 2. The Depth of Inheritance Tree is high thus
  increasing the design complexity.
• Therefore, you may want to reduce the use of
  Inheritance.
• 3. The Number of Children for this class is high
  thus diluting the abstraction of the parent class
  and increasing the amounf of testing.
• Therefore, you may want to reduce the number of
  children.
• 4. The Coupling between object classes is high
  thus reducing the reusability of a class and
  complicating modifications and testing
• Therefore, you may want to reduce the number of
  collaborator class by combining similar
  collaborators.
• 5. The Response for a class is high thus
  increasing the testing effort, test sequence and
  the overall design complexity of the class
• Therefore, you may want to reduce the number of
  operations that maybe execute in response to a
  message recieved
• 6. The Lack of Cohesion in Methods is high thus
  increasing the complexity of class design
• Therefore, you may want to reduce the lack of
  cohesion in methods by breaking down the class
  into two or more seperate classes.