Software Engineering

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

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

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

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

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.

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

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

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

Constructive Cost Modeling Basic COCOMO Model: Equations Mode Effort Schedule Organic E=2.4*(KDSI) 1.05 TDEV=2.5*(E) 0.38 Semidetached E=3.0*(KDSI) 1.12 0.35 Embedded E=3.6*(KDSI) 1.20 0.32 Man-Month / Person-Month Month Effort in man-months A COCOMO man-month consists of 152 hours of working time KDSI is the Thousand Delivered Source Instructions TDEV is the number of months estimated for software development

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

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

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: FSP = Full-time equivalent Software Personnel, a measure of the equivalent number of people working on the project at a given time.

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 FSP = Full-time equivalent Software Personnel, a measure of the equivalent number of people working on the project at a given time.

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 FSP = Full-time equivalent Software Personnel, a measure of the equivalent number of people working on the project at a given time.

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 FSP = Full-time equivalent Software Personnel, a measure of the equivalent number of people working on the project at a given time.

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