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Analysis and Design
Empirical Estimation
In this model, empirically derived formulas are used to predict data that are
a required part of the software project-planning step. The empirical data are
derived from a limited sample of projects.
Resource models consist of one or more empirically derived equations. These
equations are used to predict effort (in person-month), project duration, or other
pertinent project data. There are four classes of resource models:
• Static single-variable models
• Static multivariable models
• Dynamic multivariable models
• Theoretical models
Static single-variable model has the following form
Resource = c1 X (estimated characteristics c2)
Where,
Resource could be effort, project duration, staff size, or lines of software documentation.
c1 and c2 are constants derived from data of past projects.
Estimated characteristics is line of code, effort (if estimated), or other
software characteristics.
The basic version of the Constructive
Cost Model, or COCOMO,
presented in the next section is an example of a static-variable model.
Static multivariable models also use historical data to derive empirical relationships.
A typical model of this category takes the form
Resource = c11e1 + c12e2+ .................
Where ei is the ith software characteristics and ci1,ci2 are empirically derived
constants for the ith characteristics.
In dynamic multivariable models, resource requirements are projected as a function
of time. If the model is derived empirically, resources are defined in a series
of time steps that allocate some percentage of effort (or other resource) to each
step in the software engineering process. Further, each step may be divided into
tasks. A theoretical approach to dynamic multivariable modeling hypothesizes a
continuous "resource expenditure curve" and from it, derives equations
that model behavior of the resource.
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