This book is about how you can use Extensible Markup Language (XML) and relational databases in the real world to solve real problems (as opposed to the sometimes academic world of standards bodies and other groups that promote standards usage). In other words, you can really use XML--it's not just hype. In this book, you will find concrete examples, insight into the application development life cycle as I've known it, and a discussion of the why, the how, and the where of building applications (with a special focus on Web applications) using the tools of XML and relational databases.
This book is not intended to be a comprehensive guide. It's an overview of the field, packed with good ideas and witty commentary, which should get you started in the right direction. The areas I've focused the most attention on are ones in which I have something useful to say. In other areas, I've provided an overview of concepts, and, instead of reinventing the wheel, I've included URLs that point you to useful and informative Web resources.
Who Should Read This Book?
This book is intended primarily for software developers who are managing small- to medium-scale projects. My experience is mostly from working on small development teams, where resource limitations often dictate that the person writing the requirements for a project is also the engineer in charge of design and coding. This book is written from that perspective. If you work in a larger, more structured team or environment, you may find it strange that I'm talking about requirements gathering in one sentence and data modeling in the next, but this book can also be useful to you, if applied correctly. I've organized the chapters into the different stages of application design so that you can read through the entire book or flip to a particular piece of interest. In either case, you'll come away with something useful.
Familiarity with the concepts of databases and markup languages (specifically, knowledge of HyperText Markup Language--HTML) will make this book easier to understand. If you're new to markup languages and SQL, you'll still find this book helpful in explaining how they can be used together to develop applications. In addition, I recommend you read XML: A Manager's Guide by Kevin Dick (1999) for an overview of the XML language and its features. I also recommend SQL Queries for Mere Mortals: A Hands-On Guide to Data Manipulation in SQL by Michael J. Hernandez (2000).
Why Would You Read This Book?
Good question! I started writing this book after I worked on a content management application at TheStreet.com, which is an online financial news service--essentially an electronic newspaper--complete with journalists, editors, reporters, contributors, and columnists. TheStreet.com's publishing model was "multichannel"; they published their articles to their Web site (one "channel" of publication). They also published to other channels, such as syndicating articles to other sites (Microsoft Network, Yahoo!, and so forth) and to devices (PDAs, cell phones, pagers, what-have-you). This book is a result of my experiences in building a content management strategy for TheStreet.com and an application of everything I learned during that time, combined with in-depth material that I've picked up along the way. This book is best read when you're starting work on a project that has a content management component and you're thinking of using XML and a SQL database.
The Structure of This Book
This book is broken into ten chapters, corresponding roughly to the stages of application design and development.
1. Why XML? Notice I'm not asking the more mundane question, "What is XML?" This chapter instead delves into some specific examples of why XML is useful and why you want to start building systems with it.
2. Introducing XML and SQL: A History Lesson of Sorts. Chapter 2 provides a brief description of XML, its history and structure, and what it brings to the table. A similar discussion of SQL and the rise of the relational database follows.
3. Project Definition and Management. This chapter is a primer on getting the requirements for your system down on paper. It's included because I think this step is important, and I've often seen it done badly. Chapter 3 also discusses thinking about requirements from a perspective of building a "data-oriented" application. This chapter introduces two examples: a simple e-mail application and the CyberCinema Web site.
4. Data Modeling. After you have gathered your requirements, you have to start thinking abstractly about your data. It's a tough world out there, and without a bullet-proof data model to protect you, you're going to wake up one day and realize your life has been a dismal failure.
5. XML Design. You know why you should use XML because you read Chapter 1, but do you know where you should use it? What parts of your data make sense for XML, and what parts should remain purely relational? This chapter discusses the design of your XML documents, focusing on the document type definition (DTD) as a vehicle for this discussion.
6. Getting Relational: Database Schema Design. Now that you have your data model and your XML design, how do you best write a data schema to get the job done? This chapter is brimming with helpful examples.
7. Related Standards: XSLT, XML Schema, XML Query, and Other Flora and Fauna. What do you do with all this XML once you have it? This is where the Extensible Stylesheet Language (XSL) comes into play. XSL can be used to translate XML for display or internal purposes. It can also be leveraged to aid in partial decomposition. XML Schema provides an alternative to DTDs in defining XML document structure. Query languages on the near horizon promise to query XML documents and SQL databases.
8. XML and SQL Server 2000. So how do you take all this XML and relational data and turn it into a real, living, breathing application--one that's actually useful and works? Here's one answer: Use the comprehensive XML support found in Microsoft's SQL Server 2000. This chapter presents a discussion of those features and delves into how you might use them to implement some of the strategies previously discussed.
9. Java Programming with XML and SQL. Another implementation strategy for your XML applications is to build them using the J2EE (Java 2 Enterprise Edition) framework. Chapter 9 introduces this framework and discusses some of its XML-specific features.
10. More Examples: Beyond Silly Web Sites. Chapter 10 provides other concrete examples of how to mix XML and SQL harmoniously.
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