The CBAM

1. The CBAM Cost Benefit Analysis Method A Quantitative Approach to Architecture Design Decision Making

2. CBAM • A Quantitative Approach to Architecture Design Decision Making • Not quantitative • Does compare costs and benefits • Costs are usually immediate and one-time • Benefits are future and recurring

3. ROI • Assume costs are all this year. • Maintenance? • Assume benefits start next year and go on forever • How long will it last? • ROI of 15% or 20% is OK. • Choose highest ROI.

4. Scenarios • Based on scenarios from ATAM • For each quality attribute, think of some scenarios • ATAM actually evaluates scenarios, not attributes.

5. CBAM • Collate, refine, prioritize scenarios • Assign utility for the current and desired levels of each scenario • Develop strategies for each scenario and determine quality attribute response level • Determine expected utility value • Calculate total benefit • Choose strategies based on ROI

6. CBAM • In CBAM, “assign” and “determine” mean “make an educated guess”. • Group concensus • Is a group concensus more accurate than the guess of an individual?

7. Concensus is better • Delphi method • http://www.iit.edu/~it/delphi.html • http://www.is.njit.edu/pubs/delphibook/ • anonymity, controlled feedback, and statistical response

8. Concensus is not better • Why Societies Need Dissent by Cass Sunstein • A group that stifles dissent will get concensus, and bad decisions • The best decisions are made when there are a wide variety of viewpoints and dissent and discussion are encouraged

9. CBAM • The numbers are based on educated guesses • The calculations are based on bogus numbers • Garbage in, garbage out • There is not any better way • Main value of CBAM is that it makes key people talk to each other