Foreword

This is a collection of patterns that will help you use Microsoft .NET, which contains many objects that follow patterns we’ve found useful. These objects are brought to life by the common language runtime which makes for strongly-patterned objects. An easy way to think about this is that the runtime takes care of so many aspects of an object that just the pattern parts are left. Patterns were important before the common language runtime, but now they are even more important.

You will find here a collection of patterns that you will see in most every transaction-processing Web application. These sorts of applications are really important to enterprise developers who are important to this book’s authors. This is an important focus in the here and now. Of all the pattern books that could have been written about .NET, this is the most likely to be important to you today. Thank you, authors.

I could go on about Web applications but I wanted to point out an even more interesting thing about this collection. Whenever we pull patterns together our choices say something important about how we work. Our philosophy of work runs through our selections. For example, in the Design Patterns book, [Gamma, et. al, Addison-Wesley], the philosophy was to make programs flexible. This is important, of course, and some of those patterns are included here. But there are two other philosophies present in this volume worth mentioning.

One philosophy is that in a continuously evolving environment like the enterprise, every complexity has a cost. You’ll find a variety of patterns here that at first seem contradictory. That’s because the authors know that successful enterprise applications start simple and grow over time. Something simple works for a while then it needs to be replaced. You’ll find patterns here for both the simple and its replacement. This isn’t the same as doing it wrong and then making it right. Both patterns are right, just not at the same time on a given project.

Another philosophy that runs through these patterns is that different people in the enterprise use different patterns for different purposes. Some patterns are more about the user experience than anything else. We can say that these patterns, and the people that apply them, are working in service of the user. The more these folks understand their users, the better they will be able to apply these patterns and the better their programs will be for their effort. Contrast this to classic concerns of the enterprise: efficiency, security, reliability, and so on. This collection includes patterns about these problems, too. When you apply them you will be working in service of the enterprise. It is also likely that you personally won’t apply all the patterns in this book. That doesn’t mean that you can’t read them and understand more about how at least some of your colleagues think.

Many of the patterns are backed up by specific objects already available in .NET. For these, you will find implementations that tell you how to use these objects rather than telling you how to make these objects from scratch. Traditionally, implementation examples have been included as just one section of a pattern. These are just examples meant to be understood and emulated. The implementation “patterns” included in this volume are much more. They describe the practical experience the authors have had with using specific capabilities of .NET and, as such, amount to their best advice on how to proceed.

When you find a pattern that you need and follow it to the implementation in .NET, you are using this volume as an index into the .NET libraries. The authors have organized all the patterns on a grid that categorizes the patterns according to levels of abstraction and viewpoints. Use this grid to find patterns that should be familiar. From there, you can find .NET capabilities that apply to the work you already do. You can also look around at patterns in neighboring parts of the grid. If these are familiar, move a little further. Soon you’ll find the unfamiliar and can start benefiting from the experience of others. This works even if you know more about .NET than you do about patterns. Find the patterns that talk about sections of .NET that you use, find them on the grid, and then look around.

This work is very much about helping you use the technology built into .NET. There is a temptation to enumerate the features of .NET in a work like this. The authors have worked hard to avoid this. When they did slip into a little bit of proud boasting, the reviewers, myself included, insisted that the patterns be rewritten to be the simplest advice you can use.

I’ll close by mentioning two more ways this work is important. The pattern community has invested a decade finding, writing, and reviewing patterns in what would have to be called an academic tradition of impartiality. This work is different. It is clearly in the sponsor’s interest to have .NET well understood and this volume has that goal. However, that the sponsor would invest effort writing patterns is their acknowledgment that the decade of work has merit. The pattern community should be proud and should respond by reading, reviewing, debating, and enlarging this work.

Finally, enterprise developers and administrators should study these and other patterns not just because they offer advice that can be applied immediately, but because they provide a vocabulary to talk about intellectual property independent of that property. Consider this work a first step in a new conversation with a company that wants to succeed by serving you. Your participation in a public dialog represents a sweet-spot for interacting with a vendor that lies somewhere between focus groups and the traditional code release cycle. It is a new way for a big corporation to listen.

Ward Cunningham of Cunningham & Cunningham, Inc.
January, 2003