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brief explanation of software development projects / products cocomo stages classification examples

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  1. 1. COCOMO Constructive Cost Estimation Model Harshdeep Singh M.Tech(CE)-PT 11471011
  2. 2. Definition • Predicts the effort and schedule for a software development projects. • Based upon inputs: – Size of the software(KLOC). – Number of cost drivers that affect productivity.
  3. 3. Class. of S/w Development Projects • COCOMO was developed by Barry Boehm in 1981 • Barry postulated that any Software Development Project can be classified on the development complexity • Three categories : – Organic Type – Semi-detached Type – Embedded Type
  4. 4. Organic • Development project can be considered of organic type : – The project is developed in a familiar, stable environment – Size of the development team is reasonably small – The team members are experienced in developing similar types of projects.
  5. 5. Semi-detached – Development consists of a mixture of experienced and inexperienced staff. – Team members may have limited experience on related systems – Unfamiliar with some aspects of the system being developed
  6. 6. Embedded – Project which is complex in nature – Eg1. software being developed is strongly coupled to complex hardware – Eg2. project characterized by inflexible constraints and interface requirements. – An embedded mode project will require a great deal of innovation. – Air traffic control system
  7. 7. Some assumptions • Primary cost driver is the Delivered Line Of Code (LOC) • 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
  8. 8. Stages of COCOMO • Basic COCOMO • Intermediate COCOMO • Complete/Detailed COCOMO
  9. 9. Basic COCOMO • Basic COCOMO is good for quick, early, rough order of magnitude estimates of software costs(EFFORT & SCHEDULE) • Gives a approx. estimate of project parameters
  10. 10. Cont.. The basic COCOMO estimation model is given by the following expressions: Effort = a1 х (KLOC)a2 PM Tdev = b1 x (Effort)b2 Months Where • KLOC is Kilo Lines of Code (size of project), • a1, a2, b1, b2 are constants for each category of project, • Tdev is the estimated time to develop the software, • Effort expressed in person months (PMs).
  11. 11. Person-Month 10 persons should work for 1 month 1 person should be employed for 10 months •The effort estimation is expressed in units of person- months (PM). •It should be carefully noted that an effort of 10 PM does not imply •What it means :  10 person effort typically in 10 months
  12. 12. Person-month curve • person-months (PM) denoted by the area under the person-month curve
  13. 13. Constants of projects • The values of a1, a2, b1, b2 for different categories of products :
  14. 14. 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: – Effort = 3.0*(32)^1.12 = 146 PM – Schedule = 2.5*(146) ^0.35 = 14 months – Cost required = 146*15000 = Rs.2,19,000 - – Average Staffing = 146 PM /14 months = 10
  15. 15. Limitation • Its accuracy is necessarily limited because of its lack of factors which have a significant influence on software costs : – Hardware constraints – Use of modern tools and techniques. etc • Assumption that the entire project cost is incurred on account of the manpower cost alone.
  16. 16. Intermediate COCOMO • Basic COCOMO model assumes that effort and development time are functions of the product size alone • The intermediate COCOMO model refines the initial estimate obtained using the basic COCOMO by using a set of 15 cost drivers
  17. 17. Cost attributes • The cost drivers are grouped into four categories : – Software Product Attributes – Computer Attributes – Personnel Attributes – Project Attributes
  18. 18. Cost attributes
  19. 19. Cont.. • Consider in expression by term “Effort Adjustment Factor” (EAF). • The intermediate Cocomo takes the form. – E=a1(KLOC)^a2*EAF • where E:Effort • KLOC : Kilo lines of code • EAF : It is the effort adjustment factor
  20. 20. Complete/Detailed COCOMO • Major shortcoming of both the basic and intermediate COCOMO models is that they consider a software product as a single homogeneous entity. • For example, some sub-systems may be considered as organic type, some semidetached, and some embedded. • This approach reduces the margin of error in the final estimate.
  21. 21. Example • A distributed Management Information System (MIS) product for an organization have the following sub- components: – Database part – Graphical User Interface (GUI) part – Communication part • The costs for these three components can be estimated separately, and summed up to give the overall cost of the system
  22. 22. Thank You