Patterns of Enterprise Application Architecture

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Overview

The practice of enterprise application development has benefited from the emergence of many new enabling technologies. Multi-tiered object-oriented platforms, such as Java and .NET, have become commonplace. These new tools and technologies are capable of building powerful applications, but they are not easily implemented. Common failures in enterprise applications often occur because their developers do not understand the architectural lessons that experienced object developers have learned.

Patterns of Enterprise Application Architecture is written in direct response to the stiff challenges that face enterprise application developers. The author, noted object-oriented designer Martin Fowler, noticed that despite changes in technology--from Smalltalk to CORBA to Java to .NET--the same basic design ideas can be adapted and applied to solve common problems. With the help of an expert group of contributors, Martin distills over forty recurring solutions into patterns. The result is an indispensable handbook of solutions that are applicable to any enterprise application platform.

This book is actually two books in one. The first section is a short tutorial on developing enterprise applications, which you can read from start to finish to understand the scope of the book's lessons. The next section, the bulk of the book, is a detailed reference to the patterns themselves. Each pattern provides usage and implementation information, as well as detailed code examples in Java or C#. The entire book is also richly illustrated with UML diagrams to further explain the concepts.

Armed with this book, you will have the knowledge necessary to make important architectural decisions about building an enterprise application and the proven patterns for use when building them.

The topics covered include

· Dividing an enterprise application into layers

· The major approaches to organizing business logic

· An in-depth treatment of mapping between objects and relational databases

· Using Model-View-Controller to organize a Web presentation

· Handling concurrency for data that spans multiple transactions

· Designing distributed object interfaces

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Editorial Reviews

From Barnes & Noble
The Barnes & Noble Review
Enterprise software projects can be mind-numbingly complex. First, you need to create a system of objects that can handle all the unique situations and minuscule variations businesses must create in order to win and keep customers. Then you have to map to databases, connect user interfaces, and provide interfaces to remote and external applications. And you have to do it all on time, on budget, with technologies so new nobody fully understands them.

Fortunately, Martin Fowler’s on your side. In his new book, the legendary Fowler (known for Refactoring, among other classics) identifies 40 recurring patterns for enterprise development: design ideas that make sense whether you’re working with J2EE, .NET, or even Smalltalk.

Fowler’s solutions run the gamut, from defining your application’s layers and organizing its business logic to organizing web presentations (tip: If you’re already using the MVC pattern, you just might be getting it wrong). Fowler covers concurrency, session state, distribution strategies, architecture, object-relational behavior and structure, metadata, and a whole lot more. Along the way, he offers plenty of Java code, some C# code, and loads of UML diagrams. If your software projects require you to master complexity, this book will be indispensable. Bill Camarda

Bill Camarda is a consultant, writer, and web/multimedia content developer. His 15 books include Special Edition Using Word 2000 and Upgrading & Fixing Networks For Dummies®, Second Edition.

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Product Details

  • ISBN-13: 9780321127426
  • Publisher: Addison-Wesley
  • Publication date: 11/28/2002
  • Series: Addison-Wesley Signature Series
  • Edition description: New Edition
  • Pages: 533
  • Sales rank: 333,961
  • Product dimensions: 7.60 (w) x 9.60 (h) x 1.30 (d)

Meet the Author

Martin Fowler is an independent consultant who has applied objects to pressing business problems for more than a decade. He has consulted on systems in fields such as health care, financial trading, and corporate finance. His clients include Chrysler, Citibank, UK National Health Service, Andersen Consulting, and Netscape Communications. In addition, Fowler is a regular speaker on objects, the Unified Modeling Language, and patterns.

0321127420AB07242003

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Read an Excerpt

In the spring of 1999 I flew to Chicago to consult on a project being done by ThoughtWorks, a small but rapidly growing application development company. The project was one of those ambitious enterprise application projects: a back-end leasing system. Essentially it deals with everything that happens to a lease after you've signed on the dotted line: sending out bills, handling someone upgrading one of the assets on the lease, chasing people who don't pay their bills on time, and figuring out what happens when someone returns the assets early. That doesn't sound too bad until you realize that leasing agreements are infinitely varied and horrendously complicated. The business "logic" rarely fits any logical pattern, because, after all, it's written by business people to capture business, where odd small variations can make all the difference in winning a deal. Each of those little victories adds yet more complexity to the system.

That's the kind of thing that gets me excited: how to take all that complexity and come up with a system of objects that can make the problem more tractable. Indeed, I believe that the primary benefit of objects is in making complex logic tractable. Developing a good Domain Model (116) for a complex business problem is difficult but wonderfully satisfying.

Yet that's not the end of the problem. Our domain model had to be persisted to a database, and, like many projects, we were using a relational database. We also had to connect this model to a user interface, provide support to allow remote applications to use our software, and integrate our software with third-party packages. All of this on a new technology called J2EE, which nobody in the world had any real experience in using.

Even though this technology was new, we did have the benefit of experience. I'd been doing this kind of thing for ages with C++, Smalltalk, and CORBA. Many of the ThoughtWorkers had a lot of experience with Forte. We already had the key architectural ideas in our heads, and we just had to figure out how to apply them to J2EE. Looking back on it three years later, the design is not perfect but it has stood the test of time pretty damn well.

That's the kind of situation this book was written for. Over the years I've seen many enterprise application projects. These projects often contain similar design ideas that have proven effective in dealing with the inevitable complexity that enterprise applications possess. This book is a starting point to capture these design ideas as patterns.

The book is organized in two parts, with the first part a set of narrative chapters on a number of important topics in the design of enterprise applications. These chapters introduce various problems in the architecture of enterprise applications and their solutions. However, they don't go into much detail on these solutions. The details of the solutions are in the second part, organized as patterns. These patterns are a reference, and I don't expect you to read them cover to cover. My intention is that you read the narrative chapters in Part 1 from start to finish to get a broad picture of what the book covers; then you dip into the patterns chapters of Part 2 as your interest and needs drive you. Thus, the book is a short narrative book and a longer reference book combined into one.

This is a book on enterprise application design. Enterprise applications are about the display, manipulation, and storage of large amounts of often complex data and the support or automation of business processes with that data. Examples include reservation systems, financial systems, supply chain systems, and many others that run modern business. Enterprise applications have their own particular challenges and solutions, and they are different from embedded systems, control systems, telecoms, or desktop productivity software. Thus, if you work in these other fields, there's nothing really in this book for you (unless you want to get a feel for what enterprise applications are like.)

There are many architectural issues in building enterprise applications. I'm afraid this book can't be a comprehensive guide to them. In building software I'm a great believer in iterative development. At the heart of iterative development is the notion that you should deliver software as soon as you have something useful to the user, even if it's not complete. Although there are many differences between writing a book and writing software, this notion is one that I think the two share. That said, this book is an incomplete but (I trust) useful compendium of advice on enterprise application architecture. The primary topics I talk about are

  • Layering of enterprise applications
  • Structuring domain (business) logic
  • Structuring a Web user interface
  • Linking in-memory modules (particularly objects) to a relational database
  • Handling session state in stateless environments
  • Principles of distribution

The list of things I don't talk about is rather longer. I really fancied writing about organizing validation, incorporating messaging and asynchronous communication, security, error handling, clustering, application integration, architectural refactoring, structuring rich-client user interfaces, among other topics. However, because of space and time constraints and lack of cogitation, you won't find them in this book. I can only hope to see some patterns for this work in the near future. Perhaps I'll do a second volume someday and get into these topics, or maybe someone else will fill these and other gaps.

Of these, message-based communication is a particularly big issue. People who are integrating multiple applications are increasingly making use of asynchronous message-based communication approaches. There's much to be said for using them within an application as well. This book is not intended to be specific for any particular software platform. I first came across these patterns while working with Smalltalk, C++, and CORBA in the late '80s and early '90s. In the late '90s I started to do extensive work in Java and found that these patterns applied well to both early Java/CORBA systems and later J2EE-based work. More recently I've been doing some initial work with Microsoft's .NET platform and find the patterns apply again. My ThoughtWorks colleagues have also introduced their experiences, particularly with Forte. I can't claim generality across all platforms that have ever been or will be used for enterprise applications, but so far these patterns have shown enough recurrence to be useful.

I have provided code examples for most of the patterns. My choice of language for them is based on what I think most readers are likely to be able to read and understand. Java is a good choice here. Anyone who can read C or C++ can read Java, yet Java is much less complex than C++. Essentially most C++ programmers can read Java but not vice versa. I'm an object bigot, so I inevitably lean to an OO language. As a result, most of the code examples are in Java. As I was working on the book, Microsoft started stabilizing its .NET environment, and its C# language has most of the same properties as Java for an author. So I did some of the code examples in C# as well, although that introduced some risk since developers don't have much experience with .NET and so the idioms for using it well are less mature. Both are C-based languages, so if you can read one you should be able to read both, even if you aren't deeply into that language or platform. My aim was to use a language that the largest amount of software developers can read, even if it's not their primary or preferred language. (My apologies to those who like Smalltalk, Delphi, Visual Basic, Perl, Python, Ruby, COBOL, or any other language. I know you think you know a better language than Java or C#. All I can say is I do, too!)

The examples are there for inspiration and explanation of the ideas in the patterns. They aren't canned solutions; in all cases you'll need to do a fair bit of work to fit them into your application. Patterns are useful starting points, but they are not destinations.

Who This Book Is For

I've written this book for programmers, designers, and architects who are building enterprise applications and who want to improve either their understanding of architectural issues or their communication about them.

I'm assuming that most of my readers will fall into two groups: those with modest needs who are looking to build their own software and readers with more demanding needs who will be using a tool. For those of modest needs, my intention is that these patterns should get you started. In many areas you'll need more than the patterns will give you, but I'll provide you more of a headstart in this field than I got. For tool users I hope this book will give you some idea of what's happening under the hood and also help you choose which of the tool-supported patterns to use. Using, say, an object-relational mapping tool still means that you have to make decisions about how to map certain situations. Reading the patterns should give you some guidance in making the choices.

There is a third category; those with demanding needs who want to build their own software. The first thing I'd say here is to look carefully at using tools. I've seen more than one project get sucked into a long exercise at building frameworks, which wasn't what the project was really about. If you're still convinced, go ahead. Remember in this case that many of the code examples in this book are deliberately simplified to help understanding, and you'll find you'll need to do a lot tweaking to handle the greater demands you face.

Since patterns are common solutions to recurring problems, there's a good chance that you have already come across some of them. If you've been working in enterprise applications for a while, you may well know most of them. I'm not claiming to present anything new in this book. Indeed, I claim the opposite—this is a book of (for our industry) old ideas. If you're new to this field, I hope the book will help you learn about these techniques. If you're familiar with the techniques, I hope the book will help you communicate and teach them to others. An important part of patterns is trying to build a common vocabulary, so you can say that this class is a Remote Facade (388) and other designers will know what you mean.

Martin Fowler, Melrose, Massachusetts, August 2002

0321127420P10162002

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Table of Contents

Preface.

Who This Book Is For.

Acknowledgements.

Colophon.

Introduction.

Architecture.

Enterprise Applications.

Kinds of Enterprise Application.

Thinking About Performance.

Patterns.

The Structure of the Patterns.

Limitations of These Patterns.

I. THE NARRATIVES.

1. Layering.

The Evolution of Layers in Enterprise Applications.

The Three Principal Layers.

Choosing Where to Run Your Layers.

2. Organizing Domain Logic.

Making a Choice.

Service Layer.

3. Mapping to Relational Databases.

Architectural Patterns.

The Behavioral Problem.

Reading in Data

Structural Mapping Patterns.

Mapping Relationships.

Inheritance.

Building the Mapping.

Double Mapping.

Using Metadata.

Database Connections.

Some Miscellaneous Points.

Further Reading.

4. Web Presentation.

View Patterns.

Input Controller Patterns.

Further Reading.

5. Concurrency (by Martin Fowler and David Rice).

Concurrency Problems.

Execution Contexts.

Isolation and Immutability.

Optimistic and Pessimistic Concurrency Control.

Preventing Inconsistent Reads.

Deadlocks.

Transactions.

ACID.

Transactional Resources.

Reducing Transaction Isolation for Liveness.

Business and System Transactions.

Patterns for Offline Concurrency Control.

Application Server Concurrency.

Further Reading.

6. Session State.

The Value of Statelessness.

Session State.

Ways to Store Session State.

7. Distribution Strategies.

The Allure of Distributed Objects.

Remote and Local Interfaces.

Where You Have to Distribute.

Working with the Distribution Boundary.

Interfaces for Distribution.

8. Putting it all Together.

Starting With the Domain Layer.

Down to the Data Source.

Data Source for Transaction Script.

Data Source Table Module (125).

Data Source for Domain Model (116).

The Presentation Layer.

Some Technology-Specific Advice.

Java and J2EE.

.NET.

Stored Procedures.

Web Services.

Other Layering Schemes.

II. THE PATTERNS.

9. Domain Logic Patterns.

Transaction Script.

How It Works.

When to Use It.

The Revenue Recognition Problem.

Example: Revenue Recognition (Java).

Domain Model.

How It Works.

When to Use It.

Further Reading.

Example: Revenue Recognition (Java).

Table Module.

How It Works.

When to Use It.

Example: Revenue Recognition with a Table Module (C#).

Service Layer(by Randy Stafford).

How It Works.

When to Use It.

Further Reading.

Example: Revenue Recognition (Java).

10. Data Source Architectural Patterns.

Table Data Gateway.

How It Works.

When to Use It.

Further Reading.

Example: Person Gateway (C#).

Example: Using ADO.NET Data Sets (C#).

Row Data Gateway.

How It Works.

When to Use It.

Example: A Person Record (Java).

Example: A Data Holder for a Domain Object (Java).

Active Record.

How It Works.

When to Use It.

Example: A Simple Person (Java).

Data Mapper.

How It Works.

When to Use It.

Example: A Simple Database Mapper (Java).

Example: Separating the Finders (Java).

Example: Creating an Empty Object (Java).

11. Object-Relational Behavioral Patterns.

Unit of Work.

How It Works.

When to Use It.

Example: Unit of Work with Object Registration (Java) (by David Rice).

Identity Map.

How It Works.

When to Use It.

Example: Methods for an Identity Map (Java).

Lazy Load.

How It Works.

When to Use It.

Example: Lazy Initialization (Java).

Example: Virtual Proxy (Java).

Example: Using a Value Holder (Java).

Example: Using Ghosts (C#).

12. Object-Relational Structural Patterns.

Identity Field.

How It Works.

When to Use It.

Further Reading.

Example: Integral Key (C#).

Example: Using a Key Table (Java).

Example: Using a Compound Key (Java).

Foreign Key Mapping.

How It Works.

When to Use It.

Example: Single-Valued Reference (Java).

Example: Multitable Find (Java).

Example: Collection of References (C#).

Association Table Mapping.

How It Works.

When to Use It.

Example: Employees and Skills (C#).

Example: Using Direct SQL (Java).

Example: Using a Single Query for Multiple Employees (Java) (by Matt Foemmel and Martin Fowler).

Dependent Mapping.

How It Works.

When to Use It.

Example: Albums and Tracks (Java).

Embedded Value.

How It Works.

When to Use It.

Further Reading.

Example: Simple Value Object (Java).

Serialized LOB.

How It Works.

When to Use It.

Example: Serializing a Department Hierarchy in XML (Java).

Single Table Inheritance.

How It Works.

When to Use It.

Example: A Single Table for Players (C#).

Loading an Object from the Database.

Class Table Inheritance.

How It Works.

When to Use It.

Further Reading.

Example: Players and Their Kin (C#).

Concrete Table Inheritance.

How It Works.

When to Use It.

Example: Concrete Players (C#).

Inheritance Mappers.

How It Works.

When to Use It.

13. Object-Relational Metadata Mapping Patterns.

Metadata Mapping.

How It Works.

When to Use It.

Example: Using Metadata and Reflection (Java).

Query Object.

How It Works.

When to Use It.

Further Reading.

Example: A Simple Query Object (Java).

Repository (by Edward Hieatt and Rob Mee).

How It Works.

When to Use It.

Further Reading.

Example: Finding a Person's Dependents (Java).

Example: Swapping Repository Strategies (Java).

14. Web Presentation Patterns.

Model View Controller.

How It Works.

When to Use It.

Page Controller.

How It Works.

When to Use It.

Example: Simple Display with a Servlet Controller and a JSP View (Java).

Example: Using a JSP as a Handler (Java).

Example: Page Handler with a Code Behind (C#).

Front Controller.

How It Works.

When to Use It.

Further Reading.

Example: Simple Display (Java).

Template View.

How It Works.

When to Use It.

Example: Using a JSP as a View with a Separate Controller (Java).

Example: ASP.NET Server Page (C#).

Transform View.

How It Works.

When to Use It.

Example: Simple Transform (Java).

Two Step View.

How It Works.

When to Use It.

Example: Two Stage XSLT (XSLT).

Example: JSP and Custom Tags (Java).

Application Controller.

How It Works.

When to Use It.

Further Reading.

Example: State Model Application Controller (Java).

15. Distribution Patterns.

Remote Facade.

How It Works.

When to Use It.

Example: Using a Java Session Bean as a Remote Facade (Java).

Example: Web Service (C#).

Data Transfer Object.

How It Works.

When to Use It.

Further Reading.

Example: Transferring Information about Albums (Java).

Example: Serializing Using XML (Java).

16. Offline Concurrency Patterns.

Optimistic Offline Lock (by David Rice).

How It Works.

When to Use It.

Example: Domain Layer with Data Mappers (165) (Java).

Pessimistic Offline Lock (by David Rice).

How It Works.

When to Use It.

Example: Simple Lock Manager (Java).

Coarse-Grained Lock (by David Rice and Matt Foemmel).

How It Works.

When to Use It.

Example: Shared Optimistic Offline Lock (416) (Java).

Example: Shared Pessimistic Offline Lock (426) (Java).

Example: Root Optimistic Offline Lock (416) (Java).

Implicit Lock (by David Rice).

How It Works.

When to Use It.

Example: Implicit Pessimistic Offline Lock (426) (Java).

17. Session State Patterns.

Client Session State.

How It Works.

When to Use It.

Server Session State.

How It Works.

When to Use It.

Database Session State.

How It Works.

When to Use It.

18. Base Patterns.

Gateway.

How It Works.

When to Use It.

Example: A Gateway to a Proprietary Messaging Service (Java).

Mapper.

How It Works.

When to Use It.

Layer Supertype.

How It Works.

When to Use It.

Example: Domain Object (Java).

Separated Interface.

How It Works.

When to Use It.

Registry.

How It Works.

When to Use It.

Example: A Singleton Registry (Java).

Example: Thread-Safe Registry (Java) (by Matt Foemmel and Martin Fowler).

Value Object.

How It Works.

When to Use It.

Money.

How It Works.

When to Use It.

Example: A Money Class (Java) (by Matt Foemmel and Martin Fowler).

Special Case.

How It Works.

When to Use It.

Further Reading.

Example: A Simple Null Object (C#).

Plugin (by David Rice and Matt Foemmel).

How It Works.

When to Use It.

Example: An Id Generator (Java).

Service Stub (by David Rice).

How It Works.

When to Use It.

Example: Sales Tax Service (Java).

Record Set.

How It Works.

When to Use It.

References

Index. 0321127420T10162002

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Preface

In the spring of 1999 I flew to Chicago to consult on a project being done by ThoughtWorks, a small but rapidly growing application development company. The project was one of those ambitious enterprise application projects: a back-end leasing system. Essentially it deals with everything that happens to a lease after you've signed on the dotted line: sending out bills, handling someone upgrading one of the assets on the lease, chasing people who don't pay their bills on time, and figuring out what happens when someone returns the assets early. That doesn't sound too bad until you realize that leasing agreements are infinitely varied and horrendously complicated. The business "logic" rarely fits any logical pattern, because, after all, it's written by business people to capture business, where odd small variations can make all the difference in winning a deal. Each of those little victories adds yet more complexity to the system.

That's the kind of thing that gets me excited: how to take all that complexity and come up with a system of objects that can make the problem more tractable. Indeed, I believe that the primary benefit of objects is in making complex logic tractable. Developing a good Domain Model (116) for a complex business problem is difficult but wonderfully satisfying.

Yet that's not the end of the problem. Our domain model had to be persisted to a database, and, like many projects, we were using a relational database. We also had to connect this model to a user interface, provide support to allow remote applications to use our software, and integrate our software with third-party packages. All of this on a new technology called J2EE, which nobody in the world had any real experience in using.

Even though this technology was new, we did have the benefit of experience. I'd been doing this kind of thing for ages with C++, Smalltalk, and CORBA. Many of the ThoughtWorkers had a lot of experience with Forte. We already had the key architectural ideas in our heads, and we just had to figure out how to apply them to J2EE. Looking back on it three years later, the design is not perfect but it has stood the test of time pretty damn well.

That's the kind of situation this book was written for. Over the years I've seen many enterprise application projects. These projects often contain similar design ideas that have proven effective in dealing with the inevitable complexity that enterprise applications possess. This book is a starting point to capture these design ideas as patterns.

The book is organized in two parts, with the first part a set of narrative chapters on a number of important topics in the design of enterprise applications. These chapters introduce various problems in the architecture of enterprise applications and their solutions. However, they don't go into much detail on these solutions. The details of the solutions are in the second part, organized as patterns. These patterns are a reference, and I don't expect you to read them cover to cover. My intention is that you read the narrative chapters in Part 1 from start to finish to get a broad picture of what the book covers; then you dip into the patterns chapters of Part 2 as your interest and needs drive you. Thus, the book is a short narrative book and a longer reference book combined into one.

This is a book on enterprise application design. Enterprise applications are about the display, manipulation, and storage of large amounts of often complex data and the support or automation of business processes with that data. Examples include reservation systems, financial systems, supply chain systems, and many others that run modern business. Enterprise applications have their own particular challenges and solutions, and they are different from embedded systems, control systems, telecoms, or desktop productivity software. Thus, if you work in these other fields, there's nothing really in this book for you (unless you want to get a feel for what enterprise applications are like.)

There are many architectural issues in building enterprise applications. I'm afraid this book can't be a comprehensive guide to them. In building software I'm a great believer in iterative development. At the heart of iterative development is the notion that you should deliver software as soon as you have something useful to the user, even if it's not complete. Although there are many differences between writing a book and writing software, this notion is one that I think the two share. That said, this book is an incomplete but (I trust) useful compendium of advice on enterprise application architecture. The primary topics I talk about are

  • Layering of enterprise applications
  • Structuring domain (business) logic
  • Structuring a Web user interface
  • Linking in-memory modules (particularly objects) to a relational database
  • Handling session state in stateless environments
  • Principles of distribution

The list of things I don't talk about is rather longer. I really fancied writing about organizing validation, incorporating messaging and asynchronous communication, security, error handling, clustering, application integration, architectural refactoring, structuring rich-client user interfaces, among other topics. However, because of space and time constraints and lack of cogitation, you won't find them in this book. I can only hope to see some patterns for this work in the near future. Perhaps I'll do a second volume someday and get into these topics, or maybe someone else will fill these and other gaps.

Of these, message-based communication is a particularly big issue. People who are integrating multiple applications are increasingly making use of asynchronous message-based communication approaches. There's much to be said for using them within an application as well. This book is not intended to be specific for any particular software platform. I first came across these patterns while working with Smalltalk, C++, and CORBA in the late '80s and early '90s. In the late '90s I started to do extensive work in Java and found that these patterns applied well to both early Java/CORBA systems and later J2EE-based work. More recently I've been doing some initial work with Microsoft's .NET platform and find the patterns apply again. My ThoughtWorks colleagues have also introduced their experiences, particularly with Forte. I can't claim generality across all platforms that have ever been or will be used for enterprise applications, but so far these patterns have shown enough recurrence to be useful.

I have provided code examples for most of the patterns. My choice of language for them is based on what I think most readers are likely to be able to read and understand. Java is a good choice here. Anyone who can read C or C++ can read Java, yet Java is much less complex than C++. Essentially most C++ programmers can read Java but not vice versa. I'm an object bigot, so I inevitably lean to an OO language. As a result, most of the code examples are in Java. As I was working on the book, Microsoft started stabilizing its .NET environment, and its C# language has most of the same properties as Java for an author. So I did some of the code examples in C# as well, although that introduced some risk since developers don't have much experience with .NET and so the idioms for using it well are less mature. Both are C-based languages, so if you can read one you should be able to read both, even if you aren't deeply into that language or platform. My aim was to use a language that the largest amount of software developers can read, even if it's not their primary or preferred language. (My apologies to those who like Smalltalk, Delphi, Visual Basic, Perl, Python, Ruby, COBOL, or any other language. I know you think you know a better language than Java or C#. All I can say is I do, too!)

The examples are there for inspiration and explanation of the ideas in the patterns. They aren't canned solutions; in all cases you'll need to do a fair bit of work to fit them into your application. Patterns are useful starting points, but they are not destinations.

Who This Book Is For

I've written this book for programmers, designers, and architects who are building enterprise applications and who want to improve either their understanding of architectural issues or their communication about them.

I'm assuming that most of my readers will fall into two groups: those with modest needs who are looking to build their own software and readers with more demanding needs who will be using a tool. For those of modest needs, my intention is that these patterns should get you started. In many areas you'll need more than the patterns will give you, but I'll provide you more of a headstart in this field than I got. For tool users I hope this book will give you some idea of what's happening under the hood and also help you choose which of the tool-supported patterns to use. Using, say, an object-relational mapping tool still means that you have to make decisions about how to map certain situations. Reading the patterns should give you some guidance in making the choices.

There is a third category; those with demanding needs who want to build their own software. The first thing I'd say here is to look carefully at using tools. I've seen more than one project get sucked into a long exercise at building frameworks, which wasn't what the project was really about. If you're still convinced, go ahead. Remember in this case that many of the code examples in this book are deliberately simplified to help understanding, and you'll find you'll need to do a lot tweaking to handle the greater demands you face.

Since patterns are common solutions to recurring problems, there's a good chance that you have already come across some of them. If you've been working in enterprise applications for a while, you may well know most of them. I'm not claiming to present anything new in this book. Indeed, I claim the opposite--this is a book of (for our industry) old ideas. If you're new to this field, I hope the book will help you learn about these techniques. If you're familiar with the techniques, I hope the book will help you communicate and teach them to others. An important part of patterns is trying to build a common vocabulary, so you can say that this class is a Remote Facade (388) and other designers will know what you mean.

Martin Fowler, Melrose, Massachusetts, August 2002

0321127420P10162002

Read More Show Less

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Sort by: Showing all of 7 Customer Reviews
  • Anonymous

    Posted December 2, 2003

    Great Book!

    This is excellent book for anyone who develops enterprise architecture. Book offers many insightfull examples of the specific patterns and it provides highly useful information. Patterns of Enterprise Architecture is a must for all systems developers.

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  • Anonymous

    Posted November 24, 2002

    If you write enterprise applications, you need this book.

    This book sets forth essentially everything I've learned over the past twelve years or so about how to write enterprise applications (and many things I hadn't learned -- and now won't have to learn the hard way) in clear and easy-to-understand language. All of Mr. Fowler's books are worth reading. This one, along with Refactoring (ISBN 0201485672), are on the closest shelf to my computer and (I expect) will remain there for years to come.

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  • Anonymous

    Posted October 31, 2008

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    Posted October 2, 2009

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    Posted November 16, 2008

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    Posted May 25, 2010

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    Posted April 26, 2010

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