Newsletter Discussion

Abstract

RSS (RDF Site Summary) is a method of describing news or other Web content that is available for "feeding" (distribution and syndication) from an online publisher to Web users. A News Aggregator is software that periodically reads a set of news sources in one of several XML-based formats, finds the new bits, and displays them in reverse-chronological order on a single page.

RSS News Feeds

RSS (RDF Site Summary) is a method of describing news or other Web content that is available for "feeding" (distribution or syndication) from an online publisher to Web users. RSS is an application of the Extensible Markup Language (XML) that adheres to the World Wide Web Consortium's Resource Description Framework (RDF). Originally developed by Netscape for its browser's Netcenter channels, the RSS specification is now available for everyone to use.

The RDF Site Summary is actually an extension to the RDF language. Quoting the official RSS 1.0 specification: "RDF Site Summary (RSS) is a lightweight multipurpose extensible metadata description and syndication format. RSS is an XML application, conforms to the W3C's RDF Specification and is extensible via XML namespace and/or RDF based modularization".

Atom feed is another flavor of the news feeds concept based on XML. RSS v1.0 which is RDF based is more verbose than XML based atom feed.

A News Aggregator is a software that periodically reads a set of news sources in one of several XML-based formats, finds the new bits, and displays them in reverse-chronological order on a single page. Every hour the aggregator reads the "feeds" you're subscribed to. "The purpose of an RSS aggregator is that one does not have to open the freaking web browser to 100 different pages. By having the content right there in the aggregator, one can skim an entire article in the time it takes to open up a new web browser.

Autodiscovery:

Autodiscovery allows the client and / or software agent (aggregator) to locate the location of the RSS news feeds when he knows the base URL of the site. For example, say an end user wishes to subscribe to the RSS feed of a site. Their RSS feed-aware aggregator client could prompt them to enter the home page of the site. The client could retrieve the HTML source of the home page, find the RSS autodiscovery element, and then retrieve the RSS feed or cache the URI of the RSS feed for later retrieval. An autodiscovery in HTML looks like

<link rel="alternate" type="application/rdf+xml" title="RSS" href="http://www.example.org/rss.rdf" />

Mozilla Firefox and Feed Autodiscovery:

Among the new features in Firefox 1.0 Preview Release is Live Bookmarks, which lets users view an RSS or Atom feed as a bookmark folder. Firefox takes advantage of RSS Autodiscovery to determine the availability of a feed for your page. For an RSS feed:

<link rel="alternate" type="application/rdf+xml" title="RSS" href="http://www.example.com/yourrssfilename.rdf">

And for an Atom feed:

<link rel="alternate" type="application/atom+xml" title="Atom" href="http://www.example.com/youratomfilename.xml">

Band width Usage:

Bandwidth usage grows faster than the ability to keep up with when number of clients subscribed the RSS news feed. Terabytes of bandwidth are being used up by RSS. The content in the RSS feeds sometimes becoming lighter to avoid the bandwidth usage problem. This cannot be a proper solution and in fact it tampers the main purpose of the RSS news feeds. "HTTP delta encoding" proposes a solution to many bandwidth usage problems not only due to HTTP but also due to RSS feeds (RFC3229).

Delta encoding in HTTP:

HTTP requests cause many times the retrieval of slightly modified instances of resources for which the client already has a cache entry. Modifications are minor in many cases. In such cases, HTTP would make more efficient use of network bandwidth if it could transfer only a minimal description of the changes. The difference or the changes is called as delta encoding.

References:

• RSS 1.0 specification
• www-rdf-interest@w3.org mail archive
• RFC3229
• http://jclark.org/weblog/WebDev/Blogging/autodiscovery.html
• Atom Feed Autodiscovery