본 포스트는 개인 스터디 용으로 작성된 Ian Sommerville의 Software Engineering, 8/E의 요약본입니다.16. The COCOMO Model
- An empirical model based on project experience
- Long history from initial version published in 1981(COCOMO-81) through various instantiations to COCOMO2
- COCOMO2 takes into account different approaches to S/W development, reuse, etc.
17. COCOMO2
- COCOMO81 was developed with the assumptions that a waterfall process would be used and all S/W would be developed from scratch
- COCOMO2 incorporates a range of sub-models that produce increasingly detailed S/W estimates
- The sub-models in COCOMO2
1) Application composition model : Used when S/W iscomposed from existing parts, based on number of Application Points
2) Early design model : used when requirements are available but design has not yet started, based on number of Function Points
3) Reuse model : used to compute the effort of integrating reusable components, based on reused or generated LOC
4) Post-architecture model : used once the system architecture has been designed and more information about the system is available, based on LOC
18. Application composition model
- Supports prototyping projects and projects where there is extensive reuse
- based on standard estimates of developer productivity in application(object) points/month
- takes CASE tool use into account
- PM = (NAP * (1 - %REUSE/10)) / PROD. PM is the effort in Person-Month(工數), NAP is the number of application points, %REUSE is the amount of reused codes and PROD is productivity(unit : LOC/PM)
19. Early design model (Early prototyping model)
- Estimates can be made after the requirements have been agreed
- based on a standard formular for algorithmic models
1) PM = A * Size^B * M
2) A is 2.94 in initial calibration, Size in KLOC, B varies from 1.1 to 1.24 depending on novelty of the project development flexibility, risk management approaches and the process maturity
3) M is multiplier that reflect the capability of developer and the non-functional requirements
20. The reuse model
- takes into account reusable code that requires little or no change and has to be adapted to be integrated with new code
- two versions :
1) Black-box reuse(non-modification of source code).
2) White -box reuse(code is modified)
- Non-linear model. The more reusable code, the code decreased.
- For generated code : PM = (ASLOC * AT)/ATPROD
1) ASLOC is the number of lines of generated code(unit : LOC)
2) AT is the percentage of code automatically generated
3) ATPROD is the productivity of engineers in integrating this code(e.g. 2400 LOC/PM)
21. Post architecture model
- uses the same formula as the early design model but with 17 rather than 7 associated multipliers.
- The code size is estimated as
1) Number of lines of new code to be developed
2) estimate of equivalent number of lines of new code computing using the reuse model
3) An estimate of the number of lines of code that have to be modified according to requirements changes
- Due to its complexity, most company would not adapt this model
22. Project duration and staffing
- As well as effort estimation, managers must estimate the calendar time required to complete a project and when staff will be required
- Calendar time can be estimated using a COCOMO2 formula
1) TDEV = 3 * PM^(0.33 + 0.2 * (B - 1.01))
2) B is exponent computed as discussed above (B is for the early prototyping model)
- The time required is independent of the number of people working on the project. The key is on the net effort
23. Staffing requirements
- Staff required can't be computed by dividing the development time by the required schedule
- The number of people working on a project varies depending on the phase of the project
- The more people who work on the project, the more total effort is usually required
- A very rapid build-up of people often correlates with schedule slippage
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