DSQI (Design Structure Quality Index)

DSQI is an architectural design metric used to evaluate a computer program's design structure and the efficiency of its modules. The metric was developed by the United States Air Force Systems Command.

The result of DSQI calculations is a number between 0 and 1. The closer to 1, the higher the quality. It is best used on a comparison basis, i.e., with previous successful projects.

First Following Factor are checked and calculate their values: 

S1 =  The total number of modules defined in the Program Architecture. 

S2 =  The number of modules whose correct function depends on the source of data input or that produce data to be used elsewhere.

S3 =  The number of modules whose correct function depends on prior processing. 

S4 =  The number of database items (includes data objects and all attributes that define objects). 

S5 =  The total number of unique database items. 

S6 =  The number of database segments (different records or individual objects). 

S7 =  The number of modules with a single entry and exit (exception processing is not considered to be a multiple exit).

Once values s1 through s7 are determined for a computer program, the following intermediate values can be computed:

D1-Program structure:
If the architectural design was developed using a distinct method (e.g., data flow-oriented design or object-oriented design), then D1 = 1, otherwise D1 = 0.
D2-Module independence: 
                     D₂ = 1 - (S2/S1) 
D3-Modules not dependent on prior processing: D₃ = 1 - (s3/s1) 
D4-Database size: D₄ = 1 - (s5/s4) 
D5-Database compartmentalization: D₅ = 1 - (s6/s4) 
D6-Module entrance/exit characteristic: D₆ = 1 - (s7/s1) 

With these intermediate values determined, the DSQI is computed in the following manner:
                DSQI = SUM(w_iD_i)

• where i = 1 to 6, w_i is the relative weighting of the importance of each of the intermediate values, and S w_i = 1 (if all D_i are weighted equally, then w_i = 0.167).
• Value of DSQI for past designs can be determined and compared to a design that is currently under development.
• If the DSQI is significantly lower than average, further design work and review are indicated.
• If major changes are to be made to an existing design, the effect of those changes on DSQI can be calculated.