Inheritance Relationships for Disciplined Software Construction

210 Pages·2002·6.81 MB·English

by  Tracy A. Gardner PhD (auth.)

Distinguished Dissertations
Springer-V erlag London Ltd.
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Tracy A. Gardner
Inheritance
Relationships for
Disciplined Software
Construction
i
Springer
Tracy A. Gardner, PhD
UniversityofBath, Bath, BA2 7AY, UK
Series Editor
Professor C.T. van Rijsbergen
Department of Computing Science, University of Glasgow, G12 8RZ, UK
British Library Cataloguing in Publication Data
Gardner, Tracy A.
Inheritance re1ationships for disciplined software
construction. -(Distinguished dissertations)
1. Computer software -Development 2. Object-oriented methods
(Computer science)
1. Tide
005.1
ISBN 978-1-4471-1092-7
Library of Congress Cataloging-in-Publication Data
Gardner, Tracy A., 1972-
Inheritance relationships for disciplined software construction I Tracy A. Gardner.
p. cm. - (Distinguished dissertations)
Includes bibliographical references and index.
ISBN 978-1-4471-1092-7 ISBN 978-1-4471-0121-5 (eBook)
DOI 10.1007/978-1-4471-0121-5
1. Object-oriented methods (Computer science) 2. Software engineering. 1. Tide. II.
Distinguished dissertations (Springer-Verlag)
QA76.9.035 G368 2001
005.1'17-dc21
2001020905
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permitted under the Copyright, Designs and Patents Act 1988, this publication may only be
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Distinguished Dissertations ISSN 1439-9768
ISBN 978-1-4471-1092-7
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Origina11y published by Springer-Verlag London Limited in 2002
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Preface
Object-oriented inheritance has been in widespread use for a decade; it is
now realised that although inheritance is a powerful modelling tool with
many associated advantages, its benefits are not automatically conferred
on systems that simply use it. In order to lead to readily understandable,
easily maintainable systems with high levels of reuse, inheritance must be
used well. This situation is further complicated by having multiple appli
cationsofinheritance that are considered to be valid modelling techniques.
Although there are many guidelines pertaining to the use of inheritance,
advice that is suitable for one form of inheritance may not be applicable
to another. Inheritance, as currently available, is a difficult technique to
master.
In this book, we develop a model of inheritance based around five fun
damental inheritance relationships. Each relationship has a clear concep
tual basis, representing a fundamental, specialised use of inheritance, the
relationships - specialisation, variant, view, construction and evolution
can be used individually, or combined to achieve complex inheritance rela
tionships.These fiverelationships are referred to as structured inheritance
relationships (SIRs) since they introduce understandable and maintainable
abstraction hierarchies rather than the 'spaghetti' inheritance hierarchies
that result from using the same overloaded notion of inheritance to repre
sent a number of underlying conceptual relationships.
The fiveSIRs are based on current uses ofinheritance that have a sound
conceptual basis, the underlying conceptual relationships are considered
outside the restrictive context of current programming-language inheri
tance mechanisms and a detailed semantics is developed for each of the
v
VI
SIRs by considering the natural extension of these conceptual relation
ships. The resulting SIR model of inheritance replaces a confused notion
of inheritance with fivedistinct conceptual relationships, supporting more
precise modelling ofsystems and capturingthe semantic intent ofeach use
ofinheritance within a system.
Acknowledgements
Without my valuable placement year (1993-1994) spent at Intera Infor
mation Technologies Ltd (now Enviros) it is unlikely that I would have
embarked upon a PhD at all; it was during that year that I was first intro
duced to the object-oriented paradigm in depth. My colleagues there, in
particular Dr Peter Robinson, Dr MikeWilliams and Dr John Woods, pro
vided a stimulatingworking environment in which tqe current wayofdoing
things was never accepted by default and challenges to existing thinking
were encouraged.
I would also like to acknowledge numerous fellow conference attendees
at ECOOP '97 (especially the members ofthe PhDOOS workshop); OOP
SLA '97 (especially the members the Doctoral Symposium); and Object
Technology '97 and '98. The chance to discuss ideas with both researchers
and practitioners at these events contributed markedly to the maturity of
my research.
I would like to thank my supervisor Dr Claire Willis for her encour
agement and motivation throughout my PhD. She kept me on track and
provided detailed comments on successive versions of this work.
I am greatly indebted to Dr Kevin Rutherford who has offered detailed
criticism of my work, from both a theoretical and a practical perspective,
on numerous occasions. Kevin has also provided much-appreciated con
structive advice and encouragement regarding the process of completing a
PhD.
Thanks to Dr Nic Doye for casting his mathematical eye over my work
and providing valuable observations and suggestions. Over the years, Nic
viii
has always willingly answered my questions (some of them repeatedly, I'm
sure). Cheers Nic.
A general thankyou goes out to my family, friends and colleagues who
have always had confidence that I would get to the end of this, even when
I wasn't so sure.
I'd also like to thank the developers of Linux, Jt.1EX, emacs and all of
the other free software that has made working on my PhD a much more
pleasurable experience that it might otherwise have been.
Thanks to Lucinda Williams and Jimmy Dale Gilmore for keeping me
company and getting me through the final stages of writing up - even if
you didn't know you were doing it.
Finally, I would liketo thank my partner Beanz.! He has provided prac
tical help, emotional support, and when all else failed, chocolate, and has
helped me to keep things in perspective. Thanks Beanz, you are appreci
ated.
1Don't ask!
Contents
1 Introduction 1
1.1 Objectives and limitations 2
1.2 Approach . . 3
1.3 Conventions . 3
1.4 Outline . . . 5
2 Current understanding ofinheritance 9
2.1 The origin of inheritance. 9
2.2 What is inheritance? ... 13
2.3 Advantages of inheritance 16
2.4 Problems with inheritance 19
2.5 Understanding inheritance . 25
2.6 Conclusion . 34
3 Structured inheritance relationships (SIRs) 37
3.1 Context and scope . 38
3.2 Variant . 40
3.2.1 Using variant as a modelling tool 42
3.2.2 Variant subrelationships . . . . 43
3.3 View . 44
3.3.1 Using viewas a modelling tool 45
3.3.2 Viewsubrelationships . . . . . 46
3.4 Evolution . . . . .. ...... ... . . 47
3.4.1 Using evolution as a modelling tool 49
ix
x Contents
3.4.2 Evolutionsubrelationships . . . . . . . 49
3.5 Construction ..... ... . . . .. . . . . . . 51
3.5.1 Using construction as a modelling tool 52
3.5.2 Construction subrelationships . . . . . 53
3.6 Specialisation . 54
3.6.1 Using specialisation as a modelling tool. 55
3.6.2 Specialisation subrelationships . 56
3.7 Conclusion . 57
4 A new model ofinheritance 59
4.1 Underlying model . . . . . . . . . . . . . . . 59
4.1.1 The SIR notion of types and classes 59
4.1.2 Methods in the SIR model . 61
4.2 Presentation of the SIR model 64
4.2.1 Types and classes . . . . . . . . . . . 64
4.2.2 Representing the SIRs in the UML meta-model 65
4.2.3 Notation . . . . .. . . .. .. .... 66
4.3 SIR 66
4.3.1 Semantics of the SIR model element 66
4.4 SIR Specialisation . . . . . . . . . . . . 68
4.4.1 Semantics of SIR specialisation 72
4.5 SIR Variant . . . . . . . . . . . 73
4.5.1 Semantics of SIR variant. . . 76
4.6 SIR Construction . . . . . . . . . . . 77
4.6.1 Semantics of SIR construction 82
4.7 SIR View 83
4.7.1 Semantics of SIR view . . . 88
4.8 SIR Evolution . . . . . . . . . . . . 90
4.8.1 Semantics of SIR evolution . 93
4.9 Multiple inheritance in the SIR model 94
4.9.1 Homogeneous multiple inheritance 95
4.9.2 Heterogeneous multiple inheritance . 98
4.10 Relationship with other work 101
4.11 Conclusions . . . . . . . . . . . . . . . . . . 105
5 Techniques for structured use ofinheritance 107
5.1 Required architectural qualities . . . . . . . . 107
5.2 Planning techniques . . . . . . . . . . . . . . 110
5.2.1 Selecting features for a new abstraction 110
5.2.2 Reusability ofclients . . . . . . . . . . . 112
5.2.3 Separation ofreusable implementation from variants 113
5.3 Variability techniques 115
5.3.1 Construction-time variant selection . 115
5.3.2 State-based abstractions . . . 116
5.3.3 Dynamic realization variation . . . . 118