COCOMO II is a revised and extended version of the model, built upon the original COCOMO. It more easily allows the estimation of object-oriented software, software created via spiral or evolutionary models, and applications developed from commercial-off-the-shelf software. It was created, in part, to develop software cost database and tool support capabilities for continuous model improvement and to provide a quantitative analytic framework and a set of tools and techniques for evaluating the effects of software technology improvements on software life cycle costs and schedules.

During the initial conceptual phases of a project, the model uses object point estimates to compute effort. During the early design stages, when little is known about project size or project staff, unadjusted function points are used as an input to the model. After an architecture has been selected, design and development begin with SLOC input to the model.

COCOMO II provides likely ranges of estimates that represent one standard deviation around the most likely estimate. Accommodating factors that received little attention in the first version, COCOMO now adjusts for software reuse and re-engineering where automated tools are used for translation of existing software. COCOMO II also accounts for requirements volatility in its estimates.

Whereas the exponent on size in the effort equations in the original COCOMO varies with the development mode, COCOMO II uses scaling factors to generalize and replace the effects of the development mode.

The COCOMO II application composition model uses object points to perform estimates. The model assumes the use of integrated CASE tools for rapid prototyping. Objects include screens, reports, and modules in third-generation programming languages. The number of raw objects is estimated, the complexity of each object is estimated, and the weighted total (object-point count) is computed. The percentage of reuse and anticipated productivity is also estimated. With this information, an effort estimate can be computed.

COCOMO II explicitly handles the availability of additional information in later stages of a project, the nonlinear costs of reusing software components, and the effects of many factors on the diseconomies of scale. (Some of these are the turnover rate of the staff, the geographic dispersion of the team, and the "maturity" of the development process as defined by the SEI). The model also revises some coefficient values and eliminates discontinuities present in the old model (related to "development modes" and maintenance vs. adaptation).

COCOMO II is really three different models:

●  The application composition model - Suitable for projects built with modern GUI-builder tools. Based on new object points.

●  The early design model - Used to get rough estimates of a project's cost and duration before the entire architecture has been determined. It uses a small set of new cost drivers and new estimating equations, and it is based on unadjusted function points or KSLOC.

●  The post-architecture model - The most detailed COCOMO II model, to be used after the development of the project's overall architecture. It has new cost drivers, new line counting rules, and new equations.

In collaboration with Rational, Inc., COCOMO II integrates phases and milestones with those of the Rational Unified Process and has provided phase and activity distribution estimators for COCOMO II.


life cycle, cost drivers, software cost, database
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