Abstract

For frequently updated content available on the Web, the concept of content syndication has become popular. It refers to the publication of periodically updated information in a special format, RSS is currently the most popular format for this. Syndication is interesting for the reuse of information in various contexts (such as a news ticker always displaying the latest headlines), or for personal information aggregation (compiling a personalized list of news from various sources).

Updated Content

• Early Web content was static or updated very infrequently
  • there was not yet the requirement to reuse content in different contexts
• Frequently updated Web content quickly became a very common scenario
  • as commercial interests took over the Web, users should have a reason to re-visit a site
  • presenting a steady stream of new content creates the image of a live Web site
• There are two major use cases where HTML is not sufficient
  1. users want an efficient way to get the updated content from a site
  2. sites want to aggregate updated content from other sites and re-publish it
• Syndication formats are designed to support these two use cases
  • container formats for updated items
  • a small amount of metadata about these items for automated processing

End-User Aggregation

• Users often have a small number of preferred Web sites
  • news can be tracked by subscribing to their feeds
  • this requires an RSS-aware client (Firefox is not a good RSS reader)
• AJAX-based RSS could be implemented as a client-side application
  • retrieve the feed, transform it to HTML, and render the result
  • but the security restriction of XMLHttpRequest gets into the way
  • there is a way around this as used in the Ajax RSS reader
• How can users find a feed?
  • feeds have URIs (they are Web resources) and may be referenced from within HTML

<link rel="alternate" type="application/rdf+xml" title="…" href="…" />
<link rel="alternate" type="application/rss+xml" title="…" href="…" />

<link rel="alternate" type="application/atom+xml" title="…" href="…" />

Aggregation Intermediaries

• RSS is a frequently used format between content providers
  • news agencies want to distribute news items as easy as possible
  • by using a single format, producers and consumers can more easily interoperate
• The problems with RSS Versions caused publishers to look for something better
  • RSS had a head start and still is widely used
  • Atom is a much better format and will eventually replace RSS
• User-configured portals are the merger between both scenarios
  1. users select a number of feeds as their preferred information sources
  2. the feeds are presented on a single personalized Web page
  3. by sharing and re-publishing items, users are becoming aggregation intermediaries

RSS History

• The Myth of RSS Compatibility provides a good overview
• RSS is a schoolbook example for why standards are a good thing
  • RSS 0.9 was created for the My Netscape portal in March 1999
  • RSS 0.91 (a simplification) was introduced in July 1999 (as an interim solution)
  • the AOL/Netscape merger removed the format from the company's portal
  • RSS was without an owner, and different parties claimed/denied ownership
  • RSS 1.0 was created by an informal developer group
  • RSS 0.92 (and 0.93 and 0.94) were published without acknowledging RSS 1.0
  • finally, RSS 2.0 was released as a follow-up to the RSS 0.9x versions
• Using RSS has become an exercise in managing a menagerie of versions

RSS 0.9

• RSS means RDF Site Summary (or Rich Site Summary?)
  • based on an RDF draft and not compatible with the final RDF specification
  • RDF was considered too cumbersome and unstable
  • 0.90 (proto-RDF) was quickly replaced by the non-RDF 0.91 version
• RSS 0.92+ versions were developed as unilateral specifications
  • starting with RSS 0.91, RSS means Rich Site Summary
  • it is no longer built on RDF, instead it simply uses XML
  • the 0.9x branch eventually was renamed to RSS 2.0

RSS 0.91 Example

<rss version="0.91">
 <channel>
  <title>XML.com</title>
  <link>http://www.xml.com/</link>
  <description>XML.com features a rich mix of information and services for the XML community.</description>
  <language>en-us</language>
  <item>
   <title>Normalizing XML, Part 2</title>
   <link>http://www.xml.com/pub/a/2002/12/04/normalizing.html</link>
   <description>In this second and final look at applying relational normalization techniques to W3C XML Schema data modeling, Will Provost discusses when not to normalize, the scope of uniqueness and the fourth and fifth normal forms.</description>
  </item>

RSS 1.0

• RSS means RDF Site Summary (this time for real)
  • based on the final RDF specification and thus incompatible with any RSS 0.9
  • developed when the Semantic Web and RDF were first heavily marketed (1999)
  • RDF was expected to become the format for metadata on the Web
• RSS 1.0 makes heavy use of XML Namespaces
• RSS 1.0 introduces features which were not present in 0.91
  • date information for published items (very relevant for news feeds)
  • individual authors for various items in a feed
• RSS is the latest version of RDF-based RSS
  • the Semantic Web wave is not over yet, but RDF has lost its novelty appeal
  • for a more XML-oriented encoding, RSS 0.9 provides a better foundation

RSS 1.0 Example

<rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" xmlns="http://purl.org/rss/1.0/" xmlns:dc="http://purl.org/dc/elements/1.1/">
 <channel rdf:about="http://www.xml.com/cs/xml/query/q/19">
  <title>XML.com</title>
  <link>http://www.xml.com/</link>
  <description>XML.com features a rich mix of information and services for the XML community.</description>
  <language>en-us</language>
  <items>
   <rdf:Seq>
    <rdf:li rdf:resource="http://www.xml.com/pub/a/2002/12/04/normalizing.html"/>
    <rdf:li rdf:resource="http://www.xml.com/pub/a/2002/12/04/som.html"/>
    <rdf:li rdf:resource="http://www.xml.com/pub/a/2002/12/04/svg.html"/>
   </rdf:Seq>
  </items>
 </channel>
 <item rdf:about="http://www.xml.com/pub/a/2002/12/04/normalizing.html">
  <title>Normalizing XML, Part 2</title>
  <link>http://www.xml.com/pub/a/2002/12/04/normalizing.html</link>
  <description>In this second and final look at applying relational normalization techniques to W3C XML Schema data modeling, Will Provost discusses when not to normalize, the scope of uniqueness and the fourth and fifth normal forms.</description>
  <dc:creator>Will Provost</dc:creator>
  <dc:date>2002-12-04</dc:date>
 </item>

RSS 2.0

• RSS now means Really Simple Syndication
  • RSS 2.0 is the continuation of the 0.91 branch (which dropped RDF)
  • together with RSS 1.0 it is the most popular version of RSS
  • migration from 0.91 to 2.0 is easily possible
• RSS 2.0 tries to avoid the use of XML Namespaces
• RSS 2.0 is increasingly used with extensions for vendor-specific information
  • the RSS core is minimal, so many applications need extensions
  • many extensions have overlapping functionality
  • most extensions have unclear semantics and unclear versioning policies

RSS 2.0 Example

<rss version="2.0" xmlns:dc="http://purl.org/dc/elements/1.1/">
 <channel>
  <title>XML.com</title>
  <link>http://www.xml.com/</link>
  <description>XML.com features a rich mix of information and services for the XML community.</description>
  <language>en-us</language>
  <item>
   <title>Normalizing XML, Part 2</title>
   <link>http://www.xml.com/pub/a/2002/12/04/normalizing.html</link>
   <description>In this second and final look at applying relational normalization techniques to W3C XML Schema data modeling, Will Provost discusses when not to normalize, the scope of uniqueness and the fourth and fifth normal forms.</description>
   <dc:creator>Will Provost</dc:creator>
   <dc:date>2002-12-04</dc:date>
  </item>

The Case for Content Management

• RSS is very rarely produced by hand
  • by definition, RSS contains redundant information for a specific purpose
• If a Content Management System (CMS) is used, RSS can be generated
  • basic metadata can be generated by the CMS (title, author, date)
  • better tagging of content results in better tagging of feeds
  • well-tagged feeds are better foundations for large-scale reuse of feed items
• Blogging is simply a specialized case of a CMS
  • Web-based interface for controlling everything
  • strictly time-ordered sequenced of published items
  • navigation features primarily based on the time-specific facets of the blog (maybe tags)
  • all blogging tools include feed support

Consuming RSS

• RSS feeds often have quality problems
  • surprisingly often feeds do not even deliver well-formed XML
  • the use of embedded markup in RSS is not well-defined
• Writing an RSS reader from scratch is not a good idea
• There are three major tasks which RSS readers must do
  1. accept non-XML RSS feeds and fix them to be XML
  2. look at the feed contents and bring them into a unified form
  3. produce a unified view of feeds regardless of the RSS version

Not So Simple Syndication

• Syndication is a powerful concept that will remain popular
• RSS versions make the RSS life harder than necessary
• Current RSS versions are stable, but many extensions exist
• RSS will eventually be replaced by Atom