Analysis Patterns: Reusable Object Models

361 Pages·1996·3.148 MB·English

by  Martin Fowler

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Symbols for mappings

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Generalization notation

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Contents

Foreword v
Foreword vii
Preface xv

Chapter 1. Introduction 1
1.1 Conceptual Models 1
1.2 The World of Patterns 4
1.3 The Patterns in this Book 8
1.4 Conceptual Models and Business Process Reengineering 10
1.5 Patterns and Frameworks 11
1.6 Using the Patterns 11
References 14
Part 1. Analysis Patterns 15

Chapter 2. Accountability 17
2.1 Party 18
2.2 Organization Hierarchies 19
2.3 Organization Structure 21
2.4 Accountability 22
2.5 Accountability Knowledge Level 24
2.6 Party Type Generalizations 27
2.7 Hierarchic Accountability 28
2.8 Operating Scopes 30
2.9 Post 32
References 33

Chapter 3. Observations and Measurements 35
3.1 Quantity 36
3.2 Conversion Ratio 38
3.3 Compound Units 39
3.4 Measurement 41
3.5 Observation 42
3.6 Subtyping Observation Concepts 46
3.7 Protocol 46
3.8 Dual Time Record 47
IX

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x Contents
3.9 Rejected Observation 48
3.10 Active Observation, Hypothesis, and Projection 49
3.11 Associated Observation 50
3.12 Process of Observation 51
References 55
Chapter 4. Observations for Corporate Finance 57
4.1 Enterprise Segment 59
4.2 Measurement Protocol 65
4.3 Range 76
4.4 Phenomenon with Range 77
4.5 Using the Resulting Framework 82
References 83
Chapter 5. Referring to Objects 85
5.1 Name 86
5.2 Identification Scheme 88
5.3 Object Merge 90
5.4 Object Equivalence 92
References 93
Chapter 6. Inventory and Accounting 95
6.1 Account 97
6.2 Transactions 98
6.3 Summary Account 101
6.4 Memo Account 103
6.5 Posting Rules 104
6.6 Individual Instance Method 106
6.7 Posting Rule Execution 111
6.8 Posting Rules for Many Accounts 116
6.9 Choosing Entries 118
6.10 Accounting Practice 119
6.11 Sources of an Entry 122
6.12 Balance Sheet and Income Statement 123
6.13 Corresponding Account 124
6.14 Specialized Account Model 125
6.15 Booking Entries to Multiple Accounts 127
Further Reading 132 References 132
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Contents xi

Chapter 7 Using the Accounting

Models 133
7.1
Structural Models 134
7.2
Implementing the Structure 137
7.3
Setting Up New Phone Services 138
7.4
Setting Up Calls 142
7.5
Implementing Account-based Firing 143
7.6
Separating Calls into Day and Evening 143
7.7
Charging for Time 145
7.8
Calculating the Tax 148
7.9
Concluding Thoughts 150
References 155

Chapter 8. Planning 157
8.1 Proposed and Implemented Action 158
8.2 Completed and Abandoned Actions 160
8.3 Suspension 161
8.4 Plan 162
8.5 Protocol 165
8.6 Resource Allocation 168
8.7 Outcome and Start Functions 172
References 174

Chapter 9. Trading 175
9.1 Contract 176
9.2 Portfolio 180
9.3 Quote 185
9.4 Scenario 188
References 196

Chapter 10. Derivative Contracts 197
10.1 Forward Contracts 198
10.2 Options 200
10.3 Product 205
10.4 Subtype State Machines 211
10.5 Parallel Application and Domain Hierarchies 216
References 223
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xii Contents
Chapter 11. Trading Packages 225
11.1 Multiple Access Levels to a Package 226
11.2 Mutual Visibility 230
11.3 Subtyping Packages 233
11.4 Concluding Thoughts 234
References 235
Part 2. Support Patterns 237
Chapter 12. Layered Architecture for Information Systems 239
12.1 Two-Tier Architecture 240
12.2 Three-Tier Architecture 242
12.3 Presentation and Application Logic 245
12.4 Database Interaction 251
12.5 Concluding Thoughts 255
References 256
Chapter 13. Application Facades 257
13.1 A Health Care Example 258
13.2 Contents of a Facade 259
13.3 Common Methods 262
13.4 Operations 264
13.5 Type Conversions 265
13.6 Multiple Facades 267
References 269
Chapter 14. Patterns for Type Model Design
Templates 271
14.1 Implementing Associations 274
14.2 Implementing Generalization 281
14.3 Object Creation 289
14.4 Object Destruction 290
14.5 Entry Point 291
14.6 Implementing Constraints 294
14.7 Design Templates for Other Techniques 295
References 295
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Contents xiii
Chapter 15. Association Patterns 297
15.1 Associative Type 298
15.2 Keyed Mapping 301
15.3 Historic Mapping 303
References 307
Chapter 16. Afterword 309
References 310
Part 3. Appendix 311
Appendix A. Techniques and Notations 313
A.1 Type Diagrams 313
A.2 Interaction Diagrams 325
A.3 Event Diagrams 326
A.4 State Diagrams 327
A.5 Package Diagrams 328
References 330
Appendix B. Table of Patterns 331
Index 343
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Preface Not long ago, no books were available on object-oriented analysis and design. Now
there are so many that it is impossible for any practitioner to keep up with them all.
Most of these books concentrate on teaching a notation, suggesting a simple process
for modeling, and illustrating it with a few simple examples. Analysis Patterns:
Reusable Object Models is a different kind of book. Instead of focusing on the
process—how to do modeling—it concentrates on the result of the process—the
models themselves.
I am a consultant in object modeling for information systems. Clients ask me
to train staff on modeling and to provide mentoring on projects. Much of my skill
comes from a knowledge of modeling techniques and how to use them. More
important, however, is my experience in actually creating many models and
regularly seeing problems repeat themselves. Frequently I find that many aspects
of a project revisit problems I have faced before. That experience allows me to
reuse models I have built before, improve them, and adapt them to new demands.
Over the last few years, more and more people have also become aware of this
phenomenon. We have realized that the typical methodology books, though
valuable, only present the first step in a learning process that must also capture
the actual things that are built. This realization has flowered into the patterns
movement. This is a varied group of people, representing many different interests
and opinions yet sharing the goal of propagating useful patterns of software
systems.
As a result of the diversity of this patterns community, we have had difficulty
in defining the term pattern. We all think we can recognize a pattern when we see
it, we think most of us would agree in most cases, but we cannot come up with a
single definition. Here is my definition: A pattern is an idea that has been useful
in one practical context and will probably be useful in others.
I like to leave the definition quite loose because I wish to stay as close to the
underlying motivation of patterns, without adding too many restrictive
amendments. A pattern can have many forms, and each form adds specializations
that are useful for that kind of pattern. (Section 1.2 discusses the current state of
the patterns world and where this book fits in.)
This book is about patterns in analysis, patterns that reflect conceptual
structures of business processes rather than actual software implementations.
Most of the chapters discuss patterns for various business domains. Such
xv
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xvi Preface
patterns are hard to classify into traditional vertical areas (manufacturing,
finance, health care, and so on) because they are often useful in several areas.
These patterns are important because they help us to understand how people
perceive the world. It is valuable to base a computer system's design on this
perception and, indeed, to change that perception—which is where business
process reengineering (BPR) comes in.
Conceptual patterns cannot exist in isolation, however. Conceptual models
are only useful to software engineers if they can see how to implement them. In
this book I present patterns that can be used to turn conceptual models into
software, and I discuss how that software fits into an architecture for a large
information system. I also discuss specific implementation tips with the patterns.
I wrote this book because this was the book that I wanted to read when I
started out. Modelers will find ideas in this book to help them begin working in a
new domain. The patterns contain useful models, the reasoning behind their
designs, and when they should and should not be applied. With this information
a modeler can adapt the models to fit a specific problem.
The patterns in this book can also be used in reviewing models—to see what
might have been left out and to suggest some alternatives that may lead to
improvement. When I review a project, I usually compare what I see with the
patterns I have learned from previous work. I have found that being aware of
patterns in my work helps me to apply my past experiences more easily. Patterns
like this also uncover modeling issues that go beyond what can be covered in a
simple text book. By discussing why we model things the way we do, we gain a
greater understanding of how to improve our modeling, even if we don't use the
patterns directly.
Structure of this Book
This book is divided into two sections. The first section covers analysis patterns,
which are patterns from conceptual business models. They provide key
abstractions from domains such as trading, measurement, accounting, and
organizational relationships. The patterns are conceptual because they represent
the way people think about the business, rather than the way a computer system is
designed. The chapters in this section stress alternative patterns that can be used,
and the strengths and weaknesses of those alternatives. Although each pattern will
clearly be useful to those working in the same domain, the basic pattern is often
useful in other domains.
The second section focuses on support patterns, which help you use analysis
patterns. Support patterns show how analysis patterns fit into an information
systems architecture, how the constructs of conceptual models
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