How To Create A Reliable RSS Feed

By: Ted Peterson  

You probably already know what RSS is - it is a file format for syndicating news and the content of sites, in a very flexible manner. What you probably don't know is that creating a correct RSS feed is in many cases a very difficult task for webmasters. I am not talking about sites that supply just a few news a day, I am talking about sites that supply tens of news a day.

Let's take for example a shareware site. For the site to become popular, it has to be always up to date and to contain all the latest releases. So, the webmasters have to search for the new titles and add them to their databases. Many of them offer their visitors the possibility to stay informed about the latest releases using RSS feeds, which contain their names, links and short descriptions of the new releases. Visitors interested in this kind of information subscribe to the RSS feeds, using web-based or desktop aggregators, like Bloglines or SharpReader. All the aggregators query the RSS feeds every couple of hours, which is sufficient for many of the feeds, but not for all of them. It is a common practice that the feeds supply only the last 20 items, but what if, between two queries from the aggregators, appear, let's say, 43 items? Then, 23 of them wouldn't appear to the subscribers. Probably you've never thought about this, but I can assure you this situation really occurs, and you have to solve it, for you and your visitors' interest.

I will now show you a solution to this problem, implemented in PHP, one of the most used scripting languages on websites that are led by large databases. The main idea is that we will compare the date of the first and the 20th item, and if they are equal, we will run an extra query, to also add the other items that appeared in the database in the same day.

Lets suppose that the table from which we want to take the last items is named "products" and has 4 fields: "p_name" (product name), "p_added" (date when the product was added), "p_link" (product link) and "p_description" (product description). We have 2 functions, one that adds an item to the feed, and one that adds the standard elements of a RSS file, and then queries the database for the items added to the table on the current day.

function additem($t, $l, $d)
	{
	$r= "\n";
	$r.="$t\n";
	$r.="$d\n";
	$r.="$l\n";
	$r.="\n";

	return $r;
	}
function create_rss()
	{
	$r ="\n";
	$r.="\n";
	$r.=" \n";
	$r.=" Core Download - Latest 20 releases\n";
	$r.=" http://www.coredownload.com/\n";
	$r.=" The essential shareware and freeware downloads!\n";
	$r.=" en-us\n";

	$q1="SELECT * FROM `products` WHERE 1 ORDER by p_added DESC LIMIT 0,20";
	$result1 = mysql_query($q1);
	$i=0;
	while ($row = mysql_fetch_array($result1))
	      {
	      $i++;
	      if ($i==1) { $data1=$row[p_added]; }
	      $r .=additem($row[p_name], $row[p_link], $row[p_description]);
	      $data2=$row[p_added];
	      }
	if ($data1==$data2)
		{
		$q1="SELECT * FROM `products` WHERE `p_added`='$data2' LIMIT 20,1000";
		$result1 = mysql_query($q1);
		while ($row = mysql_fetch_array($result1))
		      {
		      $r .=additem($row[p_name], $row[p_link], $row[p_description]);
		      }
		}
	$r.=" \n";
	$r.=" \n";
	echo $r;
}

This article was posted on November 02, 2005  

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