What is a feed?

A feed is the most convenient way to be notified when a site changes. Instead of checking RecentChanges? every day to find out what's new, the site will send you an alert when it changes, which you can read in your news aggregator. (To receive alerts via email, you want MailPosts.) If you want to find feeds on other websites, look for terms or icons like "XML", "RSS", "Atom", "Subscribe", "Syndicate", "Bloglines", "Updates", or "News". Feeds are still fairly new, so the terms aren't standardized yet.

Feeds in PmWiki build on the WikiTrails idea. The page that is browsed with ?action=rss is treated as a WikiTrail. In the RSS feed produced, the trail page is the channel, and each item on the trail is a news item. So, you can use any RecentChanges? page, or Site.AllRecentChanges as source WikiTrail for each group and the whole site. And so long as they can edit pages, visitors can have custom feeds without asking the administrator for help. All they have to do is create a page with a wiki trail of the pages that they want update notices for.

More technically, a feed is a document written in the XML language, and following a syndication format like RSS or Atom. It will list the last N changes (N being whatever number the feed's maker decided it should be), and will give headlines. If the feed's maker decided to, there might also be summaries of the new content, or even the full text of the changed page.

How to read feeds

1. You'll need a news aggregator, which is a piece of software designed to read news feeds. Many different news aggregators are available. Some run on your own computer, either on their own or as plugins for email clients, web browsers, or newsreaders. Others are web applications that you can use from any internet-connected computer. Some are in between (technically web applications, but ones designed to run on your computer, not some remote server). Get one that you like.
2. Subscribe to the Wiki Trail you desire. Your aggregator will need the feed's address. Tack ?action=rss onto the end of the URL you want to subscribe to. So, if you wanted to subscribe to pmwiki.org's AllRecentChanges, you'd take its address http://pmwiki.org/wiki/Site/AllRecentChanges, and add ?action=rss to that. The result, http://pmwiki.org/wiki/Site/AllRecentChanges?action=rss, is the feed address for your news aggregator.

Set up feeds on your PmWiki site

Note: In addition to the support bundled with PmWiki, there is a Cookbook:RssImproved recipe in the cookbook, which supports RSS 2.0, enclosures/podcasting and improved customizability. - XES

PmWiki has the ability to output RSS v1 or RSS v2 documents by adding the line

somewhere in your local/config.php and supplying ?action=rss in the URL to a RSS aggregator (?action=rdf will output RSS v1).

What's the difference between RSS v1 and RSS v2?

Glad you asked! Back when the whole idea of RSS was invented it stood for RDF Site Summary where RDF stands for Resource Description Framework. Basically RDF was a way to describe meta-information about content using XML. The only problem with RSS back then was that it had very little to do with RDF (RDF headers were output, but the rest of the document was different XML than what RDF defined). So, anyway, this idea of RSS evolved for a time and gave birth to RSS v1.

Sometime later Dave Winer decided to redo the RSS spec and gave the acronym a new meaning -- Really Simple Syndication. Thus was born RSS v2 which was quite different from RSS v1 but still trying to accomplish the same goals.

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