27.5 FreeEnergy

I used the technique of including modules on several Web applications, and it led me to consider all the discrete elements of a Web page. Headers and footers are obvious, and so are other repeating navigational elements. Sometimes you can divide pages up into the content unique to the page, the stuff that comes before it, and the stuff that comes after it. This could be hard to maintain, however. Some of the HTML is in one file, some in another. If nothing else, you'll need to flip between two editor windows.

Consider for a moment a Web page as an object—that is, in an object-oriented way. On the surface, a Web page is a pair of html tags containing head tags and body tags. Regardless of the design or content of the page, these tags must exist, and inside them will be placed further tags. Inside the body tags a table can be placed for controlling the layout of the page. Inside the cells of the table are either links to other pages on the site or some content unique to the page.

FreeEnergy is a system that attempts to encapsulate major pieces of each page into files to be included on demand. Before I proceed, I want to state my motivations clearly. My first concern when developing a Web site is that it be correct and of the highest quality. Second is that it may be developed and maintained in minimal time. After these needs are addressed, I consider performance. Performance is considered last because of the relatively cheap cost of faster hardware. Moore's law suggests that eighteen months from now, CPU speed and memory capacity will have doubled for the same price. This doubling costs nothing but time. Also, experience has shown that a small minority of code contributes to a majority of the time spent processing. These small sections can be optimized later, leaving the rest of the code to be written as clearly as possible.

The FreeEnergy system uses more calls to include than you would find if you simply make a few includes at the top of your pages. Hits to the file system do take longer than function calls, of course. You could place everything you might need in one large file and include it on every page, but you will face digging through that large file when you need to change anything. A trade has been made between the performance of the application and the time it takes to develop and maintain it.

I called this system FreeEnergy because it seems to draw power from the environment that PHP provides. The include function in PHP is quite unique and central to FreeEnergy, especially the allowance for naming a script with a variable. The content unique to a page is called a screen. The screen name is passed to a single PHP script, which references the screen name in a large array that matches the screen to corresponding layout and navigation modules.

The FreeEnergy system breaks Web pages into five modules: action, layout, navigation, screen, and utility. Action modules perform some sort of write function to a database, a file, or possibly to the network. Only one action module executes during a request, and it is executed before the screen module. An action module may override the screen module named in the request. This is helpful in cases where an action module is attempting to process a form and the submitted data are incomplete or otherwise unsatisfactory. Action modules never send data directly to the screen. Instead, they add messages to a stack to be popped later by the layout module. It is possible that an action module will send header information, so it's important that no output be produced.

Layout modules contain just enough code to arrange the output of screen and navigation modules. They typically contain table tags for controlling the layout of a Web page. Inside the table cells, calls to include are placed. They may be invoking navigation modules or screen modules.

Navigation modules contain links and repeating elements. In the vernacular used by engineers I work with, these are "top nav," "bottom nav," and "side nav." Consider the popular site, Yahoo!. Its pages generally consist of the same navigation across the top and some at the bottom. Its top nav includes the logo and links to important areas of the site. If the Yahoo! site were coded in FreeEnergy, there would probably be a dynamic navigation module for generating breadcrumbs for the current section, such as Home > Computers and Internet > Software > Internet > World Wide Web > Servers > Server Side Scripting > PHP.

Screen modules contain the content unique to the particular page being displayed. They may be plain HTML, or they may be primarily PHP code, depending on context. A press release is static. Someone unfamiliar with PHP can prepare it. He needs only know that the screen module is an HTML fragment.

Any module may rely on a utility module in much the same way utility files are used in other contexts. Some utility modules are called with each page load. Others are collections of functions or objects related to a particular database table.

All modules are collected in a modules directory that further contains a subdirectory for each module type. To enhance security, it is placed outside of the Web server's document root. Within the document root is a single PHP script index.php. This script begins the process of calling successive modules and structuring their output with the standard HTML tags.