After the workout I gave you last time, you're probably either chomping at the bit to build another PHP application or you've decided to give up PHP programming and try growing cucumbers instead. If it's the latter, you should stop reading right now, because I can guarantee you that this concluding installment of PHP 101 has absolutely nothing to teach you about vegetable farming.
If it's the former, however, then you're going to enjoy what's coming up. Over the next few pages, I'm going to be building a simple RSS news aggregator using PHP, SQLite and SimpleXML. With this news aggregator, you can plug into RSS news feeds from all over the web, creating a newscast that reflects your needs and interests for your website. The best part: it updates itself automatically with the latest stories every time you view it!
Come on in, and let's get this show on the road!
Alphabet Soup
I'll start with the basics. What the heck is RSS anyhow?
RSS (the acronym stands for RDF Site Summary) is a format originally devised by Netscape to distribute information about the content on its My.Netscape.Com portal. The format has gone through many iterations since its introduction in early 1997 (take a look at http://backend.userland.com/stories/rss091 for information on RSS's long and complicated history) but most feeds use RSS 1.0 or RSS 0.91, both of which are lightweight yet full-featured.
RSS makes it possible for webmasters to publish and distribute information about what's new and interesting on a particular site at a particular time. This information, which could range from a list of news articles to stock market data or weather forecasts, is published as a well-formed XML document, and can therefore be parsed, processed and rendered by any XML parser - including the SimpleXML parser that is part of PHP 5.
Quite a few popular web sites make an RSS or RDF news feed available to the public at large. Freshmeat and Slashdot both have one, and so do many others, including the PEAR, PECL and Zend sites. A quick Google search for public RSS feeds will get you more links than you can shake a stick at.
An RSS document typically contains a list of resources (URLs), marked up with descriptive metadata. Here's an example:
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://purl.org/rss/1.0/">
<channel rdf:about="http://www.melonfire.com/">
<title>Trog</title>
<description>Well-written technical articles and tutorials on web technologies</description>
<link>http://www.melonfire.com/community/columns/trog/</link>
<items>
<rdf:Seq>
<li rdf:resource="http://www.melonfire.com/community/columns/trog/article.php?id=100" />
<li rdf:resource="http://www.melonfire.com/community/columns/trog/article.php?id=71" />
<li rdf:resource="http://www.melonfire.com/community/columns/trog/article.php?id=62" />
</rdf:Seq>
</items>
</channel>
<item rdf:about="http://www.melonfire.com/community/columns/trog/article.php?id=100">
<title>Building A PHP-Based Mail Client (part 1)</title>
<link>http://www.melonfire.com/community/columns/trog/article.php?id=100</link>
<description>Ever wondered how web-based mail clients work? Find out here.</description>
</item>
<item rdf:about="http://www.melonfire.com/community/columns/trog/article.php?id=71">
<title>Using PHP With XML (part 1)</title>
<link>http://www.melonfire.com/community/columns/trog/article.php?id=71</link>
<description>Use PHP's SAX parser to parse XML data and generate HTML pages.</description>
</item>
<item rdf:about="http://www.melonfire.com/community/columns/trog/article.php?id=62">
<title>Access Granted</title>
<link>http://www.melonfire.com/community/columns/trog/article.php?id=62</link>
<description>Precisely control access to information with the SQLite grant tables.</description>
</item>
</rdf:RDF>
As you can see, an RDF file is split up into clearly demarcated sections. First comes the document prolog, namespace declarations, and root element. This is followed by a <channel> block, which contains general information on the channel that is described by this RDF file. In the example above, the channel is Melonfire's Trog column, which gets updated every week with new technical articles and tutorials.
The <channel> block contains an <items> block, which contains a sequential list of all the resources described within the RDF document. Every resource in this block corresponds to a resource described in greater detail in a subsequent <item> block. Every <item> block describes a single resource in greater detail, providing a title, an URL and a description of that resource. It's this information that our application will use to generate a personalized news feed.
Laying the Foundation
Now that you know what RSS and RDF are all about, it's time to start work. I'll begin by sitting down at a table near the window and doodling aimlessly on a sheet of paper until I figure out exactly what my application is supposed to do, piece by piece (actually, in this case, the requirements are actually pretty basic):
The application must support one or more RSS-compliant news feeds. On start-up, the application should retrieve the latest versions of these feeds, parse them and display their contents in an easy-to-read manner. A SQLite database is a good choice to store this list of feeds.
The user should be able to control the number of stories s/he picks up from each feed. For example, a user might want to display more science and health news than business news.
The application should offer the user a web-based interface to add or delete news feeds. This interface will use PHP's SQLite API to run appropriate SQL queries on the SQLite database file and alter the information stored in the database.
Keeping these requirements in mind, it's possible to design a simple database table to hold the (user-configurable) list of RSS news feeds. Here's what it might look like:
CREATE TABLE rss (
id INTEGER NOT NULL PRIMARY KEY,
title varchar(255) NOT NULL,
url varchar(255) NOT NULL,
count INTEGER NOT NULL
);
From the table above, it's clear that every news feed will have three attributes: a descriptive title, the URL to the feed itself, and a value indicating how many of the stories in the feed you would like to see displayed in your own custom news page.
Let's add some data to get things started:
INSERT INTO rss VALUES(1, 'Slashdot', 'http://slashdot.org/slashdot.rdf', 5);
INSERT INTO rss
source:http://devzone.zend.com/node/view/id/665
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