COCOMO was first published in 1981 Barry W. Boehm's Book Software engineering economics[1] as a model for estimating effort, cost, and schedule for software projects. It drew on a study of 63 projects at TRW Aerospace where Barry Boehm was Director of Software Research and Technology in 1981. The study examined projects ranging in size from 2,000 to 100,000 lines of code, and programming languages ranging from assembly to PL/I. These projects were based on the waterfall model of software development which was the prevalent software development process in 1981. References to this model typically call it COCOMO 81. In 1997 COCOMO II was developed and finally published in 2000 in the book Software Cost Estimation with COCOMO II[2]. COCOMO II is the successor of COCOMO 81 and is better suited for estimating modern software development projects. It provides more support for modern software development processes and an updated project database. The need for the new model came as software development technology moved from mainframe and overnight batch processing to desktop development, code reusability and the use of off-the-shelf software components. This article refers to COCOMO 81. COCOMO consists of a hierarchy of three increasingly detailed and accurate forms. The first level, Basic COCOMO is good for quick, early, rough order of magnitude estimates of software costs, but its accuracy is limited due to its lack of factors to account for difference in project attributes (Cost Drivers). Intermediate COCOMO takes these Cost Drivers into account and Detailed COCOMO additionally accounts for the influence of individual project phases.Basic COCOMO computes software development effort (and cost) as a function of program size. Program size is expressed in estimated thousands of lines of code (KLOC). COCOMO applies to three classes of software projects: * Organic projects - "small" teams with "good" experience working with "less than rigid" requirements * Semi-detached projects - "medium" teams with mixed experience working with a mix of rigid and less than rigid requirements * Embedded projects - developed within a set of "tight" constraints (hardware, software, operational, ...) The basic COCOMO equations take the form Effort Applied = ab(KLOC)bb [ man-months ] Development Time = cb(Effort Applied)db [months] People required = Effort Applied / Development Time [count] The coefficients ab, bb, cb and db are given in the following table. Software project ab bb cb db Organic 2.4 1.05 2.5 0.38 Semi-detached 3.0 1.12 2.5 0.35 Embedded 3.6 1.20 2.5 0.32 Basic COCOMO is good for quick estimate of software costs. However it does not account for differences in hardware constraints, personnel quality and experience, use of modern tools and techniques, and so on. Intermediate COCOMO computes software development effort as function of program size and a set of "cost drivers" that include subjective assessment of product, hardware, personnel and project attributes. This extension considers a set of four "cost drivers",each with a number of subsidiary attributes:- Cocomo (Constructive Cost Model) is a regression model based on LOC, i.e number of Lines of Code. It is a procedural cost estimate model for software projects and often used as a process of reliably predicting the various parameters associated with making a project such as size, effort, cost, time and quality. It was proposed by Barry Boehm in 1970 and is based on the study of 63 projects, which make it one of the best-documented models. The key parameters which define the quality of any software products, which are also an outcome of the Cocomo are primarily Effort & Schedule: - Effort: Amount of labor that will be required to complete a task. It is measured in person-months units.
- Schedule: Simply means the amount of time required for the completion of the job, which is, of course, proportional to the effort put. It is measured in the units of time such as weeks, months.
Different models of Cocomo have been proposed to predict the cost estimation at different levels, based on the amount of accuracy and correctness required. All of these models can be applied to a variety of projects, whose characteristics determine the value of constant to be used in subsequent calculations. These characteristics pertaining to different system types are mentioned below. Boehm’s definition of organic, semidetached, and embedded systems: - Organic – A software project is said to be an organic type if the team size required is adequately small, the problem is well understood and has been solved in the past and also the team members have a nominal experience regarding the problem.
- Semi-detached – A software project is said to be a Semi-detached type if the vital characteristics such as team-size, experience, knowledge of the various programming environment lie in between that of organic and Embedded. The projects classified as Semi-Detached are comparatively less familiar and difficult to develop compared to the organic ones and require more experience and better guidance and creativity. Eg: Compilers or different Embedded Systems can be considered of Semi-Detached type.
- Embedded – A software project with requiring the highest level of complexity, creativity, and experience requirement fall under this category. Such software requires a larger team size than the other two models and also the developers need to be sufficiently experienced and creative to develop such complex models.
All the above system types utilize different values of the constants used in Effort Calculations.
Types of Models: COCOMO consists of a hierarchy of three increasingly detailed and accurate forms. Any of the three forms can be adopted according to our requirements. These are types of COCOMO model: - Basic COCOMO Model
- Intermediate COCOMO Model
- Detailed COCOMO Model
The first level, Basic COCOMO can be used for quick and slightly rough calculations of Software Costs. Its accuracy is somewhat restricted due to the absence of sufficient factor considerations. Intermediate COCOMO takes these Cost Drivers into account and Detailed COCOMO additionally accounts for the influence of individual project phases, i.e in case of Detailed it accounts for both these cost drivers and also calculations are performed phase wise henceforth producing a more accurate result. These two models are further discussed below. Estimation of Effort: Calculations – - Basic Model –
The above formula is used for the cost estimation of for the basic COCOMO model, and also is used in the subsequent models. The constant values a and b for the Basic Model for the different categories of system: Software ProjectsabOrganic2.41.05Semi Detached3.01.12Embedded3.61.20The effort is measured in Person-Months and as evident from the formula is dependent on Kilo-Lines of code. These formulas are used as such in the Basic Model calculations, as not much consideration of different factors such as reliability, expertise is taken into account, henceforth the estimate is rough. - Intermediate Model –
The basic Cocomo model assumes that the effort is only a function of the number of lines of code and some constants evaluated according to the different software system. However, in reality, no system’s effort and schedule can be solely calculated on the basis of Lines of Code. For that, various other factors such as reliability, experience, Capability. These factors are known as Cost Drivers and the Intermediate Model utilizes 15 such drivers for cost estimation. Classification of Cost Drivers and their attributes: (i) Product attributes – - Required software reliability extent
- Size of the application database
- The complexity of the product
(ii) Hardware attributes –
- Run-time performance constraints
- Memory constraints
- The volatility of the virtual machine environment
- Required turnabout time
(iii) Personnel attributes – - Analyst capability
- Software engineering capability
- Applications experience
- Virtual machine experience
- Programming language experience
(iv) Project attributes – - Use of software tools
- Application of software engineering methods
- Required development schedule
; Cost DriversVery LowLowNominalHighVery HighProduct AttributesRequired Software Reliability0.750.881.001.151.40Size of Application Database0.941.001.081.16Complexity of The Product0.700.851.001.151.30Hardware AttributesRuntime Performance Constraints1.001.111.30Memory Constraints1.001.061.21Volatility of the virtual machine environment0.871.001.151.30Required turnabout time0.941.001.071.15Personnel attributesAnalyst capability1.461.191.000.860.71Applications experience1.291.131.000.910.82Software engineer capability1.421.171.000.860.70Virtual machine experience1.211.101.000.90Programming language experience1.141.071.000.95Project AttributesApplication of software engineering methods1.241.101.000.910.82Use of software tools1.241.101.000.910.83Required development schedule1.231.081.001.041.10The project manager is to rate these 15 different parameters for a particular project on a scale of one to three. Then, depending on these ratings, appropriate cost driver values are taken from the above table. These 15 values are then multiplied to calculate the EAF (Effort Adjustment Factor). The Intermediate COCOMO formula now takes the form:
The values of a and b in case of the intermediate model are as follows: Software ProjectsabOrganic3.21.05Semi Detached3.01.12Embeddedc2.81.20 - Detailed Model –
Detailed COCOMO incorporates all characteristics of the intermediate version with an assessment of the cost driver’s impact on each step of the software engineering process. The detailed model uses different effort multipliers for each cost driver attribute. In detailed cocomo, the whole software is divided into different modules and then we apply COCOMO in different modules to estimate effort and then sum the effort.The Six phases of detailed COCOMO are: - Planning and requirements
- System design
- Detailed design
- Module code and test
- Integration and test
- Cost Constructive model
The effort is calculated as a function of program size and a set of cost drivers are given according to each phase of the software lifecycle.
What is basic cocomo model?
COCOMO or Constructive Cost Estimation Model is a model that estimates the effort and time taken to complete the model based on the size of the source code. It includes 15 multiplying factors from different attributes of the project, and finally calculates time and effort using this information.
What are the different stages of COCOMO estimation technique?
The Basic COCOMO
E = Total effort required for the project in Man-Months (MM). D = Total time required for project development in Months (M). KLOC = the size of the code for the project in Kilo lines of code. a, b, c, d = The constant parameters for a software project.
What is COCOMO model and why it is used?
Cocomo (Constructive Cost Model) is a regression model based on LOC, i.e number of Lines of Code. It is a procedural cost estimate model for software projects and is often used as a process of reliably predicting the various parameters associated with making a project such as size, effort, cost, time, and quality.
How many stages are in COCOMO II?
To summarize, COCOMO II provides the following three-stage series of models for estimation of Application Generator, System Integration, and Infrastructure software projects: 1. The earliest phases or spiral cycles will generally involve prototyping, using the Application Composition model capabilities.
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