Databases Reference
In-Depth Information
Software Works” briefly explains how web software works and shows you the steps
that occur when a user clicks on a link in his web browser. In “Three-Tier Architec-
tures,” we discuss web database applications more formally, describing the three-tier
architecture model and how MySQL, PHP, and Apache fit that model.
We'll assume in this and the next two chapters that you're familiar with basic pro-
gramming concepts, including loops, conditionals, and expressions. We'll also assume
you're familiar with the Web and, in particular, that you understand the basic principles
of HTML markup. It doesn't matter if you don't know the details of the HTML stand-
ard, but we expect you'll understand HTML when it's shown to you. If you've never
programmed or don't know HTML, then we advise you to use one of the resources
listed in “Resources” at the end of this chapter before reading this and the next two
chapters.
How Web Software Works
Web software is very different from a conventional application. To understand, con-
sider the word processing software on your computer, an example of a traditional,
conventional tool. You start the program, then interact with it: you move between
typing, clicking on menus and widgets, and between open windows. When you're
finished, you save your files and close the application. The software is an integrated,
interactive package: you work with your documents, surrounded by the application's
tools and windows. The software developer has customized the environment to support
only word processing, and the tool is tailored carefully to that need; it has special-
purpose tools—such as floating toolbars—that are designed to help you when you're
editing a document. Also, usually, you're the only person using your word processor
on your computer.
The interface to most web software isn't specialized in the same way as a word pro-
cessor. Instead, you use a conventional web browser—probably Mozilla Firefox, In-
ternet Explorer, or Safari—that sends requests and receive responses from standar-
dized, distributed web servers. The web servers process your requests, run scripts, and
return the output to your browser; they serve the many users that are authorized to use
the software. The interface environment is constrained: you usually move back and
forward through HTML documents—much like using a setup wizard—entering data
into HTML forms or clicking on HTML widgets. The tools you use are general-purpose
browser tools—such as the Back, Forward, Refresh, and Home buttons, and the Book-
marks or Favorites menu—that don't vary with the application.
Web software itself is also different. It's distributed: a small part of it—the simple web
browser interface with its limited capabilities—resides on the user's computer, while
the majority of the application logic is captured in scripts that are on a remote web
server. The scripts aren't an integrated, large package: they are simple parts—each
performs a specific function—that together provide the application functionality when
the user follows a series of steps. Because of this, web software is limited. It isn't very
