Software development is a strenuous and risky process as there are many constraints that may be faced by the project manager at periodic intervals during the software life cycle phases [93, 2]. Such constraints hinder project managers from planning the development activities properly. These constraints may be previously determined at the beginning of the SDLC or they may emerge accidentally at any development phase without prior notice. Accordingly, the project manager should be able to handle these constraints and be aware of them during the software development process. Examples of these constraints include schedule reduction, budget shortage, lack of testers, the unavailability of a preferred QA technique etc.
In the following example it will be shown how effective our model is when deal- ing with such constraints and how it can give the project manager the flexibility and the proactivity to control them. For the sake of simplicity we chose one single constraint as an example which is budget shortage.
7.3.1
Budget Shortage Constraint
Referring to our example of company x as is shown in Table 7.6, let us assume that the available budget during the development process for inspecting the High risk work prod- uct is £3000, which includes running the QA process and the defect removal activities. This amount should be invested in a way to maintain high DRE and minimise both exe- cution and escaped costs.
A few scenarios will be worked out which will cover two points:
1. Investing the whole amount in a scenario-based reading technique only.
2. Investing part of the amount in ad-hoc reading and saving the difference.
3. Using scenario-based and ad-hoc reading techniques jointly.
4. Investing the whole budget in an ad-hoc reading technique.
In all scenarios, the necessary calculations will be made to compare the results. An overview of the needed values for the scenario-based and ad-hoc-based reading tech- niques is shown in Table 7.8.
Scenario-based reading technique Ad-hoc reading technique
Variable Value Variable Value
DRE 75% DRE 50%
Cremoval
p (3 h/defect) Cremovalp (1 h/defect)
Ext 2 (p/h) Ext 1 (p/h)
Cescaped
p 40 (p/h) Cescapedp 40 (p/h)
Table 7.8: Scenario-based and Ad-hoc based Reading Techniques
only.
Technique Weight Execution time (Ext) Execution cost (Exc) & Removal cost (Rc) (Esc) Scenario-based 100% 200 hours £5800 £8000
Table 7.9: Scenario-based Outcome
As shown in Table 7.9, applying the scenario-based reading technique with a full weight coverage of 100% would generate £5800 of Exc and Rc. This value exceeds the available budget of £3000 assigned to the QA plans of the work product. In order to have the QA plan comply with the available budget, the project manager should try to decrease the overall cost of the practice used by reducing the weight value assigned to it.
Based on this decision and using Equation 5.11 and 5.12 which showed that with £3000 of Exc and Rc, the weight value given should be roughly only 52% out of the whole weight. The relative Exc and Rc for the estimated weight is shown in Table 7.10.
• 2ndScenario: Investing part of the amount in ad-hoc reading and saving the differ- ence.
Technique Weight Execution time (Ext) Execution cost (Exc) & Removal cost (Rc) (Esc) Ad-hoc based 52% 104 hours £3016 £4160
Table 7.10: Execution & Removal Cost of 52% of Work Product High
As shown in Table 7.10, only 52% of coverage ratio is given to the QA scenario- based reading technique; that is, 48% of the work product will be left uninspected
which is, in turn, injected with defects that may propagate to the system testing phase. The estimated escaped cost of the remaining 48% of the work product is calculated in order to quantify the consequences of leaving the rest of the work product uninspected. An overview is shown in Table 7.11.
Technique Weight Escaped Defect (Esc) Escaped cost (Esc)
None 48% 19 £15200
Table 7.11: Escaped Cost of 48% of Work Product
As shown in Table 7.11, the Esc soared to £15,200 which would have a negative impact on the budget of the later phases and the project manager may not favour such a scenario. To reduce the escaped cost, the project manager may decide to apply the ad-hoc based reading technique jointly with the scenario-based reading technique to both stay within the budget allowance and to mitigate the effect of the Esc value. This is clarified in the third scenario.
• 3rdScenario: Using scenario-based and ad-hoc reading techniques jointly. Using our QA system and based on Equations 5.13, 5.12, 5.11 and 5.6, the project man- ager worked out many weight distributions of applying the scenario-based reading technique and the ad-hoc reading technique. However, as stated before, the total Exc and Rc for both techniques should adhere to the constraint that it does not exceed the £3000 of the QA budget. The project manager found another option to handle this constraint in a way that the scenario-based reading would be reduced to 20% and that the remaining 80% would then be assigned to a checklist-based reading. An overview of the result is shown in Table 7.12.
Technique Weight Found defects Escaped defects (Exc)&(Rc) (Esc)
Scenario-based reading 20% 6 2 £1160 £1600
Checklist-based reading 80 % 16 16 £1920 £12800
Total 100 % 22 18 £3080 £14400
Table 7.12: Weights Distribution of Scenario-based and Ad-hoc Reading Techniques
• 4thScenario: Investing the whole budget in the ad-hoc reading technique.
This is in case the project manager decides to exclude the scenario-based reading technique from the QA plan due to its high Exc value and assign the whole QA process to the ad-hoc reading technique with a weight of 100%. The expected result of this weight distribution is illustrated in Table 7.13.
Technique Weight Found defects Escaped defects (Esc) (Exc) & (Rc) (Esc)
Ad-hoc reading 100% 20 20 £2400 £16000
Table 7.13: Ad-hoc Reading Technique QA Process
It would seem that from the last scenario, £2400 only of the available budget was invested in the Exc and Rc which yielded an overall saving of £600. This saving can be used later to reduce the total value of Esc as follows:
£16000 - £600 = £15400 Esc
However, by comparing the previous four scenarios, it can be clearly noticed that the 3rd scenario (scenario-based: 20%, ad-hoc based: 80%) outweighs the others in terms of its overall low cost and in terms of the resulting DRE value. For example, the net Esc value of the 3rd scenario is £14,400 compared with £15,400 for the 4th scenario. Accordingly,
the resulting savings for the benefit of the 4th scenrio calcualted by subtracting one value from the other is:
£15400 - £14400 = £1000