Estimating object-oriented software projects with use cases

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University of Oslo
Department of Informatics

Estimating
Object-Oriented
Software Projects
with Use Cases

Kirsten Ribu

Master of Science
Thesis

7th November 2001

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Abstract
In object-oriented analysis, use case models describe the functional requirements of a future software system. Sizing the system can be done
by measuring the size or complexity of the use cases inthe use case model.
The size can then serve as input to a cost estimation method or model, in
order to compute an early estimate of cost and effort.
Estimating software with use cases is still in the early stages. This thesis
describes a software sizing and cost estimation method based on use cases,
called the ’Use Case Points Method’. The method was created several years
ago, but is not wellknown. One of the reasons may be that the method
is best used with well-written use cases at a suitable level of functional
detail. Unfortunately, use case writing is not standardized, so there are
many different writing styles. This thesis describes how it is possible to
apply the use case points method for estimating object-oriented software,
even if the use cases are not written out in full.The work also shows how
use cases can be sized in alternative ways, and how to best write use cases
for estimation purposes. An extension of the method providing simpler
counting rules is proposed.
Two case studies have been conducted in a major software company,
and several student’s projects have been studied in order to investigate
the general usefulness of the method and its extension.The results have
been compared to results obtained earlier using the method in a different
company. The investigations show that the use case points method works
well for different types of software.
Data from the various projects have also been used as input to two
commercial cost estimation tools that attempt to estimate object-oriented
projects with use cases. The goal was to select a costestimation method
or tool for a specific software company. The findings indicate that there is
no obvious gain in investing in expensive commercial tools for estimating
object-oriented software.

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Acknowledgements
This thesis was written for my Master of Science Degree at the Department
of Informatics, the University of Oslo.
I would like to thank my advisors Bente Anda and DagSjøberg for their
support and co-operation, with special thanks to Bente who let me use her
research work for some of the investigations. I would also like to thank
everybody who contributed to this work by sharing their experience and
ideas with me: the participants on the various projects, fellow student
Kristin Skoglund for practical help, and Johan Skutle for his interest andco-operation.
I want to thank my children Teresa, Erika and Patrick for their patience
and good-will during the last hectic weeks, and my special friend Yngve
Lindsjørn for his support all the way.

Oslo November 2001
Kirsten Ribu

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Contents
1 Introduction
1.1 The Problem of Object-Oriented Software Estimation
1.2 Problem Specification and Delimitation . . . . . . . . .
1.3Contribution . . . . . . . . . . . . . . . . . . . . . . . . .
1.4 Thesis Structure . . . . . . . . . . . . . . . . . . . . . . .

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2 Cost Estimation of Software Projects
2.1 Software Size and Cost Estimation . . . . . .
2.1.1 Bottom-up and Top-down Estimation
2.1.2 Expert Opinion . . . . . . . . . . .. . .
2.1.3 Analogy . . . . . . . . . . . . . . . . . .
2.1.4 Cost Models . . . . . . . . . . . . . . . .
2.2 Function Point Methods . . . . . . . . . . . .
2.2.1 Traditional Function Point Analysis .
2.2.2 MKII Function Point Analysis . . . . .
2.3 The Cost Estimation Tools . . . . . . . . . . .
2.3.1 Optimize . . . . . . . . . . . . . . . . .
2.3.2 Enterprise Architect . . . . . . . ....
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