Handling Conflicts in Aspectual Requirements Compositions - Transactions on Aspect-Oriented Software Development - page 160

Table 14. Final Ranking (synthesis)

Contribution Stakeholders Importance Final Priorities Ranking

5 th Accuracy 0.071 0.155 0.127

2 nd Response Time 0.058 0.227 0.171

4 th Availability 0.097 0.154 0.135

6 th

Integrity 0.149 0.093 0.112

3 rd

0.168 0.167 0.168

Multi-Access

1 st Validate Card 0.288 0.140 0.189

7 th

Fault Tolerance 0.168 0.064 0.099

Let us now interpret the final ranking in Table 14 in the context of our Enter
Subway match point, where negative contributions were found between several
concerns, as shown in Fig. 3. The system can only be used with a valid card,
therefore, it is not a surprise that the concern Validate Card appears raked first.
Response Time come next in the ranking because we need to do our best to avoid
long queues. Third ranking is Multi-Access because it is important to guarantee the
use of the system by thousands of passengers at the same moment. Furthermore,
Availability needs to be accomplished first than Accuracy and Integrity 2 in order to
guarantee that the system is accessible for the passengers and helps Multi-Access and
Response Time (this is possible because Availability has positive contribution to
Response Time and Multi-Access). Accuracy appears in fifth place because his
concern contributes negatively to Response Time and Availability, which have higher
preferences for the stakeholders, so Accuracy priority needs to be lower in order to
help guaranteeing the stakeholders preferences. Integrity is ranked sixth and Fault
Tolerance comes later, in the seventh position. Fault Tolerance contributes positively
to Accuracy and Availability so its composition helps the others.
Note that the resulting raking can also be used to guide an incremental
development and even to define the composition rule, but this issue in not the focus of
this paper.

Step 5: Consistency
The AHP method provides means to evaluate the consistency of the judgements that
the decision maker demonstrated during the pairwise comparisons. This reduces any
possible error that might have been introduced during the judgement process. Since
our example was small we decided to check the consistency for all pairwise matrices
instead of just obtaining a final consistency ratio. The results using equations (2), (3)
and (4) are shown in Table 15.
The consistency indexes obtained are a good indication that logical consistent
judgments were made on all pairwise comparisons, because they are well below the
required 10% threshold, as explained in Sect. 3.1.

2 As we said before, Security has been decomposed into Integrity and Availability.