Databases Reference
In-Depth Information
Web server software
HTTP request
(request, including any form data)
HTTP response
(content, mostly HTML)
Host running database
and web servers
Web database application
User with web browser
Database server software
Figure 13-1. Running a web script
interactive, it must be fault-tolerant, it's limited by network speed bottlenecks, and it
must work with generic browsers. The relatively recent Ajax technique relies heavily
on client-side programming to deliver a more customized user interface. However, the
basic building blocks remain the same.
The advantage of web software is its flexibility. Any user, anywhere, with almost any
browser on any platform, can use the software. Importantly, no configuration is re-
quired, and training isn't usually needed. Web software is predictable: there are a limi-
ted number of ways you can build an application, and most users have seen the para-
digms before and know where to start. With web software, deployment is as simple as
setting up your web server, installing scripts on it, and publishing the address of your
web application page.
Figure 13-1 shows how web software works. When a user clicks on a link (or submits
a form, or types a URL), a request is sent from her web browser to a web server identified
by the URL. The web server extracts path, resource, and other information from the
URL and uses this to identify what script to run and what parameters to give it. The
script is then executed and its output sent to the browser, along with a status message
that indicates whether the operation was successful. If the request was successful, then
(usually) an HTML resource is displayed, and the request process starts again when
the user makes her next click in their browser.
Consider an example. You've decided to build an online store and have started to write
the scripts that compose the application. Suppose you've authored one script,
shop.php
, which allows a user to add an item to his shopping cart. The script expects
two parameters to capture what the user wants to purchase: a
productID
number that
identifies the product, and a
quantity
value that is the amount of the product. The
script outputs a success message in HTML when everything works, and an error mes-
sage in HTML when it doesn't.
To test your
shop.php
script, you can save it in a directory from which your Apache
web server serves scripts (the document root). If you're using a Linux or Mac OS X
system, you also need to make sure that the file can be read by everyone, since the web
