RSS

Introduction

Really Simple Syndication, Rich Site Summary or RDF Site Summary (depends who you ask)

An XML-based format for quickly communicating frequently-updated information across the web

You can subscribe to an RSS feed of frequently updated information

First widespread with news sites

You can subscribe to an RSS feed provided by a news site (e.g. the BBC) to get headlines, without having to actually visit the site
If the headline interests you, you can then follow the link to find out more

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RSS history

One of the main issues with RSS is that there are several versions
The currently-used versions include 0.91, 1.0 and 2.0, and an RSS derivative known as Atom

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RSS evolution

Initial version was 0.90, developed by Netscape and based on the RDF format; here, RSS stood for RDF Site Summary
0.90 evolved into 0.91, a simpler format (Rich Site Summary) which was not based on RDF
A separate group of people evolved 0.90 into 1.0, which continued to be based on RDF
0.91 then evolved into 2.0 (1.0 could not be used as it had already been used for the RDF branch
Currently, 0.91, 1.0 and 2.0 are all widely used
This makes it hard if you want to write RSS reader software, as you have to support all three versions
However, if you provide an RSS feed, you need only choose one
We will be looking at 2.0 as it has the easiest-to-understand format

RSS history

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References on RSS specifications and background

Wikipedia article
Syndicated content: it's more than just some file formats (in-depth, academic article)
RSS History
RSS 1.0 Specification
RSS 2.0 Specification

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An example of RSS


<?xml version='1.0'?>
<rss version='2.0'>

<channel>
    <title>The New Forest Guardian</title>
    <link>http://aquarius.solent.ac.uk/students/whiteleg/webapps/rss/nfg/
    </link>
    <description>The New Forest Guardian - Your top local source of
    info for the New Forest area </description>

    <item>
        <title>Open Mapping comes to the New Forest</title>
        <link>http://aquarius.solent.ac.uk/students/whiteleg/webapps/
        rss/nfg/nfgstory.php?id=2 </link>
        <description>This weekend several volunteers from all over the
        world descend on the New Forest to create a new, copyright-free
        digital map.</description>
        <pubDate>Fri, 22 Sep 2006 12:00:00 GMT</pubDate>
    </item>
    <item>
        <title>Killer Pig on the Loose !!!!!;/title>
        <link>http://aquarius.solent.ac.uk/students/whiteleg/webapps/
        rss/nfg/nfgstory.php?id=1 </link>
        <description>Man-eating pig attacks New Forest villagers
        </description> 
        <pubDate>Fri, 22 Sep 2006 12:30:00 GMT</pubDate>
    </item>
</channel>
</rss>

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Explanation of example

A channel is an RSS feed relating to one particular topic, in this case, news items in the New Forest provided by the New Forest Guardian website
The channel has three important tags describing it:
- title - the title of the feed
- link - the address of the feed
- description - a description of the feed
The channel then has a number of individual items (e.g. stories)
Each item has a:
- title - e.g. a headline
- link - URL where you can find out more
- description - a short description of the item
- pubDate - the date of publication, you can use this to select the latest items

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How is an RSS feed generated?

Imagine you wanted to create an RSS feed of updates to your website... how would you do this?
On a very basic level, you create the RSS XML file on your server and publish its URL
People can then subscribe to the feed by entering the URL into news-reading software (see below)
However this has one obvious disadvantage.. the XML would have to be manually updated each time you wanted to send out a new item!

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Auto-generation of RSS feeds

Another possibility is to generate RSS feeds dynamically using server-side scripting, e.g. PHP
For example, if you were running a news site, you could generate the feed by querying the database for the latest stories

Code example:

<?php

$conn=mysql_connect("localhost","username","password");
mysql_select_db("database");

$result=mysql_query("SELECT * FROM stories ORDER BY ID");

echo "<rss version='2.0'>";
echo "<channel>";
echo "<title>New Forest Guardian</title>";
echo "<link>http://newforestguardian.org.uk/rss.php</link>";
echo "<description>Latest stories from the NFG</description>";

while($row=mysql_fetch_array($result))
{
	echo "<item>";
	echo "<title>$row[title]</title>";
	echo "<link>fullstory.php?id=$row[ID]</link>";
	echo "<description>$row[description]</description>";
	echo "<pubDate>$row[pubDate]</pubDate>";
	echo "</item>";
}

echo "</channel>";
echo "</rss>";
mysql_close($conn);
?>

Note how the contents of each RSS tag are based on the database
Also note how the link tag contains a link to the full story; we do this by linking to another script, fullstory.php, and passing it the ID of the story as a query string

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RSS and Blogs

The newest use of RSS is in association with blogs
Blogs (weblogs) are basically online "diaries", frequently updated by their author, and used to publish all manner of things from progress on a project to random thoughts, ideas and opinions - to which readers can respond
To do your own blog, you install blogging software such as Wordpress on your web server
Blogging software automatically creates RSS feeds of each blog entry
Thus people can subscribe to your blog - and be informed of the latest entries - by subscribing to its RSS feed

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Subscribing to an RSS feed

There are a number of ways to subscribe to an RSS feed:

Newsreader software
Websites such as Bloglines
Directly through your browser: Firefox has integrated RSS support

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Newsreader software

Specialised, standalone software for reading RSS feeds
Typically contacts the RSS feed URL at regular intervals (e.g. every hour) to get the latest items

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RSS-reading websites

Websites which allow you to subscribe to an RSS feed
You specify which feed(s) you want to subscribe to
High level of control e.g. only show items less than a week old
Examples: Bloglines

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Direct browser support

Firefox has built in feed-reading support
If you visit a website with an associated RSS feed, the orange RSS icon will appear in the address bar
You can then click on the feed and it will add it to your "Live Bookmarks"
To view a given RSS feed at any time you can then:
- Go to Bookmarks-Bookmarks Toolbar Folder
- Select the feed you're interested in
- The titles of the latest items in the feed will then appear

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Publicising your feeds

Feeds often have fairly obscure URLs, e.g.

http://www.fredbloggs.com/TheBloggsBlog/myinterestingfeed.rss

To indicate that a site has an appropriate RSS feed, include a link to the feed on the main page(s)

This line of code, added to the HTML pages of the site, will also help newsreaders pick up the feed:

<link rel='alternate' type='application/rss+xml'
title='freemap rss feed' href='/webapps/rss1.rss' />

If you then enter a website address (e.g. www.free-map.org.uk) in a newsreader, it will find the RSS feed automatically

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Integrating RSS feeds into other websites

With a bit of scripting, it is possible to integrate a RSS feed made by someone else into your own website
e.g. on free-map.org.uk I might want to include the blog entries at www.opengeodata.org
There are libraries available for reading RSS, e.g. for PHP: MagpieRSS
This would work by:
- PHP script on your website requests RSS feed from another site
- RSS sent back to your site
- PHP reads the RSS and displays links to (and perhaps descriptions of) the articles