Component Level Design Metrics

Component level design metrics for software components focus on internal characteristics of a software component and include measures of the three Cs - module cohesion, coupling, and complexity.

- Cohesion Metrics :It defines a collection of metrics that provide an indication of the cohesiveness of a module.The metrics are defined in terms of five concepts :
* Data slice - data values within the module that affect the module location at which a backward trace began.
* Data tokens - Variables defined for a module
* Glue Tokens - The set of tokens lying on multiple data slices
* Superglue tokens - The set of tokens on all slices
* Stickiness - of a glue token is proportional to number of data slices that it binds
* Strong Functional Cohesion
SFC(i) = SG(i)/tokens(i)

- Coupling Metrics : Module coupling provides an indication of the connectedness of a module to other modules, global data, and the outside environment.
* Data and control flow coupling
di = number of input data parameters
ci = number of input control parameters
d0 = number of output data parameters
c0 = number of output control parameters
* Global coupling
gd = number of global variables used as data
gc = number of global variables used as control
* Environmental coupling
w = number of modules called (fan-out)
r = number of modules calling the module under consideration (fan-in)
* Module Coupling:
mc = 1/ (di + 2*ci + d0 + 2*c0 + gd + 2*gc + w + r)
mc = 1/(1 + 0 + 1 + 0 + 0 + 0 + 1 + 0) = .33 (Low Coupling)
mc = 1/(5 + 2*5 + 5 + 2*5 + 10 + 0 + 3 + 4) = .02 (High Coupling)