Interfacing Relational Databases to the Web

This document explains how to build a database-backed web site using Apache, the PHP3 module and the PostgreSQL relational database.

Why would one want to link a database to the web? A better question might be, “Why wouldn't one want to link a database to the web?” Static HTML pages are good for many things: documentation, hypertext books, personal pages and other unchanging information. However, static pages present a few problems:

  • Static pages can be a hassle to maintain. If one is managing a large site with thousands of pages, changing just the “look and feel” of the site will involve either an inordinate amount of work or a long evening with CGI and Perl. This gets even nastier when the content of the site changes.

  • Static pages don't allow for user input, feedback or collaboration. Suppose you want to add a message board to your static web site. You can set up a form that mails user comments to the webmaster, who manually puts them on a page—you can even set up a script to do this. However, this presents a few problems, as we shall discuss later.

  • Static pages don't allow you to operate a web service. One can operate a web site with static HTML, but some of the most useful web sites today, such as Slashdot (http://slashdot.org/), CNN (http://www.cnn.com/) and Amazon.com (http://www.amazon.com/), are services offering dynamic database-backed content.

A database management system provides uniform access to structured data, much like an object-oriented programming language provides a uniform way to store data and define methods to act on that data. If you're writing a program in C++ and you need to deal with strings, would you rather wrap all associated routines in a class or deal with the fact that your string is really a char * each time you operate on it? With a database, one is offered a layer of abstraction between how the data is actually stored and how one uses it, which is quite useful for several reasons. You could achieve the same results with C or Perl scripts, but it wouldn't be as pretty and could get downright ugly.

I hope this quick rundown is enough to convince you that you really want to use a database for your dynamic web site. In this article, I will present instructions for installing PHP3 (http://www.php.net/) and PostgreSQL (http://www.postgresql.org/), a little bit of theory, some instructions for using SQL and PHP3, and an example application.

Installing the Tools

This description assumes you are running Red Hat, but most of these instructions will be applicable to other distributions; these tools are fairly painless to install from source, anyway.

Here's a list of what you'll need to run the example application and develop your own applications:

  • Apache 1.3 or greater. You will need at least version 1.3, because 1.2 does not support modules, and PHP is faster and more secure as a module. On a Red Hat system, you'll need both the apache and apache-devel packages. (Make sure you have the file apxs installed, because we're going to recompile the PHP3 Apache module.)

  • The source RPM for PHP3, version 3.0 or greater.

  • PostgreSQL 6.4 or greater; the example code will not run on version 6.3 without a little editing, because 6.4 has an SQL parser.

To rebuild PHP3 for PostgreSQL support, take the following steps:

  1. Use su to become root.

  2. Install the source RPM for PHP3 (rpm -ihv mod_php3-3.0.5-2.src.rpm on Red Hat 6.0). This will place a “spec file” in the directory /usr/src/redhat/SPECS and a tar file of the source in /usr/src/redhat/SOURCES. Since the PHP module that comes with Red Hat doesn't have database support enabled by default, we'll have to recompile it. RPM makes this fairly painless.

  3. Because the PHP3 installation process assumes a default PostgreSQL installation, not the Red Hat one, we'll need to make some symlinks. Create a directory /usr/local/pgsql and make symbolic links from /usr/include/pgsql to /usr/local/pgsql/include and from /usr/lib/ to /usr/local/pgsql/lib.

  4. Invoke your favorite editor on the spec file (mod_php3.spec) and search for ./configure; then add the configure option --with-pgsql.

  5. Now build a binary package with rpm: /rpm -bb mod_php3.spec/

  6. If all goes well, you'll have a binary package in /usr/src/redhat/RPMS/arch, where /arch is your architecture. Install it, and you're ready to move on.

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