Page 141 - DCAP304_DCAP515_SOFTWARE_PROJECT_MANAGEMENT

Unit 6: Effort Estimation

 Detailed COCOMO: Advanced COCOMO model incorporates all characteristics of the Notes
intermediate version with an assessment of the cost driver’s impact on each step, like
analysis, design, etc. In this case the breakdown to phases is not realized in percentages
but by means of influence factors allocated to the phases. At the same time, it is
differentiated according to the three levels of the product hierarchy (module, subsystem,
system); product-related influence factors are now taken into consideration in the
corresponding estimation equations.

6.7.3 Appraisal of the Model

Applications of COCOMO

 Medium and Large Projects: For small projects, the attempt for an estimation according to
intermediate and detailed COCOMO is too high; but the results from basic COCOMO
alone are not sufficiently exact.
 Technical Application: For software projects developing commercial applications,
COCOMO usually comes up with overstated effort estimation values therefore COCOMO
is only applied for the development of technical software. This circumstance is due to the
fact that the ratio DSI and man months implemented in the COCOMO estimation equation
fits the efficiency rate in a technical development; with regard to commercial software
development a higher productivity rate DSI/man-month can be assumed.

Strong and Weak Points of the Model and Possible Remedial Measures

 Estimation Base “Delivered Source Instructions”: By means of estimation base instructions
(DSI) it was attempted to diminish the great uncertainties and problems in connection with
the traditional estimation base LOC. However, some problems remain: the ambiguity of a
DSI estimation and for the development effort the DSI are-based on modern software
engineering methods-no longer of great importance since the effort increasingly occurs
during the early activities and DSI will only be effective towards the end of the development
process; DSI as well as LOC depends on the selected programming language (an Ada adoption
to COCOMO is already available, however). A remedy can be achieved by the weighting of
instructions according to their various types compiler, data description, transformation,
control, and I/O instruction, data description instructions (differentiated according to
integration degree, message/data object, modification degree) and processing instructions
(differentiated according to batch/on-line, modification degree, complexity, language)).
 Macro and Micro Estimation: By means of the different levels of the model, COCOMO
makes it possible to realize both a macro estimation by means of Basic COCOMO and a
micro estimation by means of Intermediate COCOMO and Detailed COCOMO. The micro
estimation allows the effort allocation to activities and functional units. However, method
COCOMO is not only based on a software life cycle deviating from the V-Model but also
on another system structure. Therefore, in order to list individual efforts for sub models,
(sub-) activities, and (sub-) products, it is necessary to adjust these items of method
COCOMO to the V-Model concept.

 Influence Factors/Objectivity: In the effort estimation, COCOMO takes into consideration
the characteristics of the project, the product, and the personnel as well as of the technology.
In order to achieve an objective evaluation of these influence factors, COCOMO offers
exact definitions. The quantification of influence factors represents a certain problem,
though which has a strong impact on the quality of the estimation method and on the
required DSI information.

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