Supporting Software Architecture Evolution Supporting Software Architecture Evolution

289 Pages·2003·2.51 MB·English

S Blekinge Institute of Technology
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Doctoral Dissertation Series No. 2003:03
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t Supporting Software Architecture Evolution
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n Architecture Selection and Variability
Mikael Svahnberg
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Department of Software Engineering and Computer Science
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ISBN 91-7295-025-0 rg Blekinge Institute of Technology
Blekinge Institute of Technology
Doctoral Dissertation Series No 2003:03
ISSN 1650-2159
ISBN 91-7295-025-0
Supporting Software Architecture Evolution
Architecture Selection and Variability
Mikael Svahnberg
Department of Software Engineering and Computer Science
Blekinge Institute of Technology
Sweden
Blekinge Institute of Technology
Doctoral Dissertation Series No. 2003:03
ISSN 1650-2159
ISBN 91-7295-025-0
Published by Blekinge Institute of Technology
© 2003 Mikael Svahnberg
Cover photography, “Heliga Kors Kyrka”
© 2003 Mikael Svahnberg
Printed in Sweden
Kaserntryckeriet, Karlskrona 2003

This thesis is submitted to the Faculty of Technology at Blekinge Institute of Technology,
in partial fulfillment of the requirements for the degree of Doctor of Philosophy in Software
Engineering
Contact Information
Mikael Svahnberg
Department of Software Engineering and Computer Science
Blekinge Institute of Technology
PO Box 520
SE-372 25 Ronneby
SWEDEN
E-mail: [e-mail]
Abstract
Today it is more a rule than an exception that software systems have a
lifecycle of more than several years. Hence, software evolution is inevita-
ble. During the life span of a software system the domain in which the
system is working evolves and changes. This causes changes to the soft-
ware system, and the software system may also be evolved to satisfy new
markets. The ability to evolve gracefully, and thus the long-term success
of a software system, is to a large extent governed by its software archi-
tecture and the ability of the software architecture to fulfil requirements
on quality attributes and to adapt to evolving requirements.
In this thesis we study evolution of software architectures and what can
be done to support this evolution. We focus on three particular aspects of
evolution support: how to ensure that the correct blend of quality
attributes is met (architecture selection), the technical means available for
supporting changes in the software system (variability), and what types of
changes that are likely to occur during evolution (categories of evolution).
We introduce a method for architecture evaluation and selection that
focus on ensuring that the selected software architecture is the architec-
ture candidate with the most potential for fulfilling a particular blend of
quality attributes. The method is based on quantification of expert opin-
ions and focused discussions where these expert opinions differ. The
architecture evaluation and selection method is studied in both an aca-
demic and in an industry setting.
We also introduce a taxonomy of techniques for realising variability in a
software system and study how the techniques in this taxonomy are
applied in different evolution situations. The taxonomy is based on sev-
eral industry case studies. Two industry cases are studied in further detail
and the evolution of these systems are followed over a number of releases
and generations. During this evolution it is shown how variability mecha-
nisms are used to also support evolution, and that there are typical cases
of evolution that a software system can be prepared to cope with.
The contribution of this thesis is that it increases the understanding of
how evolution occurs in a software system, how to create software that is
flexible enough to support evolution and how to evaluate and select a
software architecture that meets a particular blend of quality attributes.
Together this ensures that a software system is based on a software archi-
tecture that fits the current quality requirements and that is flexible in the
right places so that it is able to evolve gracefully.
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Acknowledgements
First, I would like to express my gratitude to my advisor Prof. Claes Wohlin,
who is always an invaluable source of ideas, criticism and cheerful prod-
ding. Thanks to Prof. Jan Bosch, my advisor during my first two years, for
offering me this chance and for helping me through the early phases.
Thanks to Dr. Michael Mattsson for always having plenty of inspiring ideas.
For fruitful cooperation I also thank Prof. Lars Lundberg and Dr. Jilles van
Gurp. I would also like to thank my colleagues (including but not limited
to the SERL research group) that have contributed with ideas and input,
as well as participation in different investigations.
I would like to thank the companies I have had the pleasure of working
together with during different phases of my Ph.D. studies: Axis Communi-
cations, Ericsson, UIQ Technology and Danaher Motion Särö.
As always, I am grateful to my parents, Alison and Kenneth, for their inces-
sant support and for helping me achieve all this. My brother Charlie has
also been a valuable source of inspiration.
Finally I thank all my friends, without whom life would be quite dreary.
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Contents
CHAPTER 1 Introduction..................................................................1
Outline of Thesis...........................................................................4
Research Approach........................................................................4
Concepts and Related Work..........................................................16
Part I Software Architecture Evaluation and Selection
CHAPTER 2 A Software Architecture Vision .....................................43
Contribution of Part I....................................................................44
Outline of Part I...........................................................................45
Architecture Evaluation and Selection.............................................46
CHAPTER 3 Architecture Evaluation and Selection ...........................49
Scope and Goal of Chapter............................................................50
Context of Method........................................................................50
Architecture Evaluation and Selection.............................................52
A Case Study Using the Method.....................................................61
Discussion....................................................................................66
Summary and Conclusions............................................................66
CHAPTER 4 Consensus Discussion and Analysis...............................69
Scope and Goal of Chapter............................................................70
Create Individual Frameworks.......................................................72
Discuss Individual Frameworks......................................................73
Create a Unified Framework..........................................................75
Evaluation of Unified Framework...................................................76
Analysis of Framework..................................................................78
Summary and Conclusions............................................................81
CHAPTER 5 Study 1: Academic Evaluation......................................83
Scope and Goal of Chapter............................................................83
Study Design................................................................................85
Operation....................................................................................90
Analysis and Interpretation...........................................................91
Summary and Conclusions............................................................97
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CHAPTER 6 Evaluation using Multiple Sources...............................101
Scope and Goal of Chapter..........................................................102
Comparing Two Views................................................................103
Analysis and Interpretation.........................................................108
Summary and Conclusions..........................................................109
CHAPTER 7 Study 2: Industrial Application....................................111
Scope and Goal of Chapter..........................................................111
Planning....................................................................................113
Operation..................................................................................119
Analysis and Interpretation.........................................................123
Summary and Conclusions..........................................................128
CHAPTER 8 Composing the Evaluation Team ................................131
Scope and Goal of Chapter..........................................................131
Research Method........................................................................132
Data Sets...................................................................................136
Analysis.....................................................................................136
Discussion..................................................................................142
Summary and Conclusions..........................................................143
CHAPTER 9 Summary and Conclusions.........................................145
Summary and Conclusions for Part I............................................145
Future Work...............................................................................147
Part II Evolution and Variability
CHAPTER 10 Evolution and Variability ............................................151
Contribution of Part II.................................................................152
Outline of Part II........................................................................153
Features, Evolution and Variability...............................................153
CHAPTER 11 Criteria and a Taxonomy for Variability .......................157
Scope and Goal of Chapter..........................................................157
Introducing Variability in Software Products..................................158
Variability Realisation Techniques................................................169
Case Studies..............................................................................189
Conclusions................................................................................195
CHAPTER 12 Evolution Using Variability..........................................197
Scope and Goal of Chapter..........................................................197
Case 1: StorageServer................................................................199
Case 2: Billing Gateway System...................................................210
Summary...................................................................................217
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CHAPTER 13 Evolution Patterns.....................................................219
Scope and Goal of Chapter..........................................................219
Evolution of the Two Cases.........................................................220
Summary...................................................................................224
CHAPTER 14 Summary and Conclusions.........................................225
Summary and Conclusions for Part II...........................................225
Future Work...............................................................................226
References ...............................................................229
APPENDIX I Data from Academic Study.........................................237
Individual Data...........................................................................237
Unified Frameworks....................................................................248
APPENDIX II Data from Industry Study ..........................................251
Individual Data...........................................................................251
Unified Frameworks....................................................................261
APPENDIX III Correlations in Industry Study....................................263
Framework for Architecture Structures.........................................263
Framework for Quality Attributes.................................................266
Prioritized Quality Attributes........................................................271
Graphs......................................................................................272
Frequency of Correlations...........................................................277
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