CONTENTS

SOFTWARE COST ESTIMATION MODEL BASED ON NEURAL NETWORKS 207
• Constraints and priorities.
One approach starts by decomposing the expected deliverable of the project into
manageable chunks (product breakdown structure), using it to build a work breakdown
structure (WBS) and making a direct estimation of the required effort using
expert opinion (experienced professionals who can make estimations based on previous
experience). Size of the project and required effort can be converted afterwards
in project duration and project cost using empirical formulas. Estimations made for
each phase of the project are summed up generating overall size, effort, schedule and
cost [17]. For better estimations, the results could be weighted by factors (e.g. complexity
of the project, familiarity of the team with the required technology or business
knowledge, risks), generating the final project estimations. In the last 3 decades different
models for software cost estimation have been proposed, ranging from empirical
models [12] to elaborated analytical models [3], [5], [16]. Empirical models use data
from previous software development projects in order to make predictions for similar
projects. The analytical model uses a formal approach, based on global presumptions,
like how well can a team member solve a task and how many issues are possible to
appear. Both approaches lead to the conclusion that accurate cost estimation in a
software development project remains a very difficult task [11].
2. Estimation process for software development
An estimation process follows a number of steps [3]:
(1) Setting cost estimation objectives;
(2) Developing a Project Plan for each request and each resource;
(3) Analyzing the software development requests;
(4) Working out as much detail about the software development project;
(5) Using an alternative cost estimation technique for cross validation;
(6) Comparison between estimations and through repeated iterations;
(7) Permanent controlling of the project during the development phase.
In order to achieve a precise estimation, no matter what cost estimation model
has been chosen, there must be a permanent fine tuning of several parameters during
the whole project development life cycle. The fine tuning can have influence on the
resource allocation strategy for the estimated software development project without
changing the overall cost estimation.
3. Software metrics
The software metrics have a great influence in the estimation of the cost of a
software development project. There are several software metrics used to estimate
the size of a software development project: Lines Of Code (LOC) and Functional
Points (FP) metrics being the most popular.
• Lines of Code metrics (LOC): this software metrics is based on the calculation
of the number of source code instructions, excepting comments. LOC metrics
is unfortunately dependent on the technology and programming language used for