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Constructive Cost Modeling with COCOMO: An Overview

This presentation provides an outline of Constructive Cost Modeling (COCOMO), including the 3 COCOMO models, project characteristics, assumptions, basic equations, when to use it, limitations, and examples. COCOMO is a widely-used software estimation model that predicts effort and schedule based on software size and cost drivers.

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Constructive Cost Modeling with COCOMO: An Overview

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  1. Software Engineering

  2. Outline of this presentation • Constructive Cost Modeling (Constructive Cost Model) • 3 COCOMO Models http://en.wikipedia.org/wiki/COCOMO • Project Characteristics • Some Assumptions • Basic COCOMO Model • Equations • When Should You Use It • Limitations • Examples

  3. Constructive Cost Modeling • COCOMO is one of the most widely used software estimation models in the world • It was developed by Barry Boehm in 1981 • COCOMO predicts the effort and schedule for a software product development based on inputs relating to the size of the software and a number of cost drivers that affect productivity

  4. Constructive Cost Modeling 3 COCOMO Models : • COCOMO has three different models that reflect the complexity: • the Basic Model • the Intermediate Model • and the Detailed Model

  5. Constructive Cost Modeling Project Characteristics • Organic Mode • Small to medium size product development • developed in a familiar, in-house & stable environment, • similar to the previously developed projects • relatively small and requires little innovation

  6. Constructive Cost Modeling Project Characteristics • Semidetached Mode • Team members have an intermediate level of experience with related systems. • Perhaps a mixture of experienced and inexperienced people. • Parts of the project may require rigorous interfaces.

  7. Constructive Cost Modeling Project Characteristics • Embedded Mode • tight, inflexible constraints and interface requirements • The product requires great innovation • Product must operate within a strongly coupled complex of H/W, S/W, regulations, and operational procedures. • Tighter requirements and more inflexible scheduling

  8. Constructive Cost Modeling Some Assumptions • Primary cost driver is the number of Delivered Source Instructions (DSI) developed by the project (LOC/KLOC) • COCOMO estimates assume that the project will enjoy good management by both the developer and the customer • Assumes the requirements specification is not substantially changed after the plans and requirements phase

  9. Constructive Cost Modeling Basic COCOMO Model • Basic COCOMO model estimates the software development effort using only a single predictor variable (size in DSI) and three software development modes

  10. Mode Effort Schedule Man-Month / Person-Month Month 1.05 0.38 Organic E=2.4*(KDSI) TDEV=2.5*(E) 1.12 0.35 Semidetached E=3.0*(KDSI) TDEV=2.5*(E) 1.20 0.32 Embedded E=3.6*(KDSI) TDEV=2.5*(E) Constructive Cost Modeling Basic COCOMO Model: Equations

  11. Constructive Cost Modeling When Should You Use It • Basic COCOMO is good for quick, early, rough order of magnitude estimates of software costs

  12. Constructive Cost Modeling Limitation of Basic COCOMO Model • Its accuracy is necessarily limited because of its lack of factors which have a significant influence on software costs • The Basic COCOMO estimates are within a factor of 1.3 only 29% of the time, and within a factor of 2 only 60% of the time

  13. Constructive Cost Modeling An Example • We have determined our project fits the characteristics of Semi-Detached mode • We estimate our project will have 32,000 Delivered Source Instructions. Using the formulas, we can estimate:

  14. Constructive Cost Modeling An Example • Effort = 3.0*(32) 1.12 = 146 Man-Months • Schedule = 2.5*(146)0.35 = 14 Months • Productivity / Man Month = 32,000 DSI / 146 MM = 219 DSI/MM • Average Staffing / Month = 146 MM /14 M = 10 Man

  15. Constructive Cost Modeling An Example Bila sebuah proyek dikelompokkan kedalam organic mode project diperkirakan akan menghasilkan 32,000 DSI, maka: PM = 2.4 * (32) 1.05 = 91 p.m. Dari nilai PM yang diperoleh dapat dihitung berapa lama proyek akan diselesaikan TDEV = 2.5 (91) 0.38 = 14 bulan

  16. Constructive Cost Modeling An Example Bila sebuah proyek dikelompokkan kedalam embedded mode project diperkirakan akan menghasilkan 128,000 DSI, maka: PM = 3.6 (128) 1.20 = 1216 p.m. Dari nilai PM yang diperoleh dapat dihitung berapa lama proyek akan diselesaikan TDEV = 2.5 (1216) 0.32 = 24 bulan

  17. Any Questions?

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