Architecting Microsoft® .NET Solutions for the Enterprise

Introduction Good judgment comes from experience, and experience comes from bad judgment. —Fred Brooks Every time we are engaged on a software project, we create a solution. We call the process architecting, and the resulting concrete artifact is the architecture. Architecture can be implicit or explicit. An implicit architecture is the design of the solution we create mentally and persist on a bunch of Microsoft Office Word documents, when not on handwritten notes. An implicit architecture is the fruit of hands-on experience, the reuse of tricks learned while working on similar projects, and an inherent ability to form abstract concepts and factor them into the project at hand. If you're an expert artisan, you don't need complex drawings and measurements to build a fence or a bed for your dog; you can implicitly architect it in a few moments. You just proceed and easily make the correct decision at each crossroad. When you come to an end, it's fine. All's well that ends well. An explicit architecture is necessary when the stakeholder concerns are too complex and sophisticated to be handled based only on experience and mental processes. In this case, you need vision, you need guidance, and you need to apply patterns and practices that, by design, take you where you need to be. What Is Architecture? The word architecture has widespread use in a variety of contexts. You can get a definition for it from the Oxford English Dictionary or, as far as software is concerned, from the American National Standards Institute/Institute of Electrical and Electronics Engineers (ANSI/IEEE) library of standards. In both cases, the definition of architecture revolves around planning, designing, and constructing something—be it a building or a software program. Software architecture is the concrete artifact that solves specific stakeholder concerns—read, specific user requirements. An architecture doesn't exist outside of a context. To design a software system, you need to understand how the final system relates to, and is embedded into, the hosting environment. As a software architect, you can't ignore technologies and development techniques for the environment of choice—for this book, the .NET platform. Again, what is architecture? We like to summarize it as the art of making hard-to-change decisions correctly. The architecture is the skeleton of a system, the set of pillars that sustain the whole construction. The architect is responsible for the architecture. The architect's job is multifaceted. She has to acknowledge requirements, design the system, ensure the implementation matches the expectation, and overall ensure that users get what they really need—which is not necessarily what they initially accept and pay for. Software architecture has some preconditions—that is, design principles—and one post condition—an implemented system that produces expected results. Subsequently, this book is divided into two parts: principles and the design of the system. The first part focuses on the role of the architect: what he does, who he interacts with and who he reports to. The architect is primarily responsible for acknowledging the requirements, designing the system, and communicating that design to the development team. The communication often is based on Unified Modeling Language (UML) sketches; less often, it's based on UML blueprints. The architect applies general software engineering principles first, and object-oriented design principles later, to break down the system into smaller and smaller pieces in an attempt to separate what is architecture (points that are hard to change) and what is not. One of the purposes of object-oriented design is to make your code easy to maintain and evolve—and easy to read and understand. The architect knows that maintainability, security, and testability need to be built into the system right from the beginning, and so he does that. The second part of the book focuses on the layers that form a typical enterprise system—the presentation layer, business layer, and data access layer. The book discusses design patterns for the various layers—including Domain Model, Model-View-Presenter, and Service Layer—and arguments about the evolution of technologies and summaries of the new wave of tools that have become a common presence in software projects—O/R mappers and dependency injection containers. So, in the end, what's this book about? It's about the things you need to do and know to serve your customers in the best possible way as far as the .NET platform is concerned. Patterns, principles, and techniques described in the book are valid in general and are not specific to particularly complex line-of-business applications. A good software architecture helps in controlling the complexity of the project. And controlling the complexity and favoring maintainability are the sharpest tools we have to fight the canonical Murphy's Law of technology: "Nothing ever gets built on schedule or within budget." The expert is the one who knows how to handle complexity, not the one who simply predicts the job will take the longest and cost the most—just to paraphrase yet another popular Murphy's Law. Who This Book Is For In the previous section, we repeatedly mentioned architects. So are software architects the ideal target audience for this book? Architects and lead developers in particular are the target audience, but any developers of any type of .NET applications likely will find this book beneficial. Everyone who wants to be an architect may find this book helpful and worth the cost. What about prerequisites? Strong object-oriented programming skills are a requirement, as well as having a good foundation of knowledge of the .NET platform and data access techniques. We point out a lot of design patterns, but we explain all of them in detail in nonacademic language with no weird formalisms. Finally, we put in a lot of effort into making this book read well. It's not a book about abstract design concepts; it is not a classic architecture book either, full of cross-references and fancy strings in square brackets that hyperlink to some old paper listed in the bibliography available at the end of the book. This is (hopefully) a book you'll want to read from cover to cover, and maybe more than once—not a book to keep stored on a shelf for future reference. We don't expect readers to pick up this book at crunch time to find out how to use a given pattern. Instead, our ultimate goal is transferring some valuable knowledge that enables you to know what to do at any point. In a certain way, we would happy if, thanks to this book, you could do more implicit architecture design on your own. Companion Content In the book, we present several code snippets and discuss sample applications, but with the primary purpose of illustrating principles and techniques for readers to apply in their own projects. In a certain way, we tried to teach fishing, but we don't provide some sample fish to take home. However, there's a CodePlex project that we want to point out to you. You find it at http://www.codeplex.com/nsk. This book also features a companion Web site where you can also find the CodePlex project. You can download it from the companion site at this address: http://www.microsoft.com/mspress/companion/9780735626096. The Northwind Starter Kit (NSK) is a set of Microsoft Visual Studio 2008 projects that form a multitier .NET-based system. Produced by Managed Design (http://www.manageddesign.it), NSK is a reference application that illustrates most of the principles and patterns we discuss in the book. Many of the code snippets in the book come directly from some of the projects in the NSK solution. If you're engaged in the design and implementation of a .NET layered application, NSK can serve as a sort of blueprint for the architecture. Refer to the Managed Design Web site for the latest builds and full source code. For an overview of the reference application, have a look at the Appendix, "The Northwind Starter Kit," in this book. Hardware and Software Requirements You'll need the following hardware and software to work with the companion content included with this book: Microsoft Windows Vista Home Premium Edition, Windows Vista Business Edition, or Windows Vista Ultimate Edition Microsoft Visual Studio 2008 Standard Edition, Visual Studio 2008 Enterprise Edition, or Microsoft Visual C# 2008 Express Edition and Microsoft Visual Web Developer 2008 Express Edition Microsoft SQL Server 2005 Express Edition, Service Pack 2 The Northwind database of Microsoft SQL Server 2000 is used by the Northwind Starter Kit to demonstrate data-access techniques. You can obtain the Northwind database from the Microsoft Download Center (http://www.microsoft.com/downloads/details.aspx?FamilyID=06616212-0356-46A0-8DA2-EEBC53A68034&displaylang=en). 1.6 GHz Pentium III+ processor, or faster 1 GB of available, physical RAM. Video (800 by 600 or higher resolution) monitor with at least 256 colors. CD-ROM or DVD-ROM drive. Microsoft mouse or compatible pointing device Find Additional Content Online As new or updated material becomes available that complements this book, it will be posted online on the Microsoft Press Online Developer Tools Web site. The type of material you might find includes updates to book content, articles, links to companion content, errata, sample chapters, and more. This Web site is available at www.microsoft.com/learning/books/online/developer and is updated periodically. Support for This Book Every effort has been made to ensure the accuracy of this book and the contents of the companion CD. As corrections or changes are collected, they will be added to a Microsoft Knowledge Base article. Microsoft Press provides support for books and companion CDs at the following Web site: http://www.microsoft.com/learning/support/books Questions and Comments If you have comments, questions, or ideas regarding the book or the companion content, or questions that are not answered by visiting the sites above, please send them to Microsoft Press via e-mail to mspinput@microsoft.com Or via postal mail to Microsoft Press Attn: Microsoft .NET: Architecting Applications for the Enterprise Editor One Microsoft Way Redmond, WA 98052-6399 Please note that Microsoft software product support is not offered through the above addresses.