RSS stands for Really Simple Syndication, or Rich Site Summary, depending on who you listen to. Either way RSS has become the poster child for the Publish-Subscribe protocol. RSS allows weblog and website owners to syndicate their content to anyone who wishes to subscribe to it. Usually people subscribe to "RSS feeds" via an aggregator. Some weblog authoring tools also support RSS subscriptions - for example Radio Userland.

The weblog community has embraced RSS. Most bloggers have RSS feeds now - even design guru Jeffrey Zeldman has signed up (and immediately defended himself against accusations that he had "sold out"!). With RSS there is less control over design - it is enough work designing for different browsers, without having to cater to multiple aggregators too! Text is primary with RSS, which I believe brings ideas to the fore.

RSS currently is used to syndicate personal content or news items. But there is another value in RSS, which is beginning to be explored more - using RSS as a means to subscribe to content by topic. RSS topic subscriptions bring us closer to the Semantic Web - defined by Tim Berners-Lee as "an extension of the current Web in which information is given well-defined meaning". Subscribing to an RSS topic feed lets a web user accurately and automatically gather information that has specific meaning to them.

Most RSS feeds currently are personal weblog and news items - which means the publisher controls the content. RSS feeds that are based on topics on the other hand, give power back to the subscriber. As an example, recently I subscribed to the BBC top stories RSS feed. But there are only a few topics I'm interested in from BCC - news on the Iraq war, British football, any technology stories that come up. I found though that a lot of the content was local British news, which I have little use for since I come from New Zealand. Eventually I unsubscribed from the BBC news feed, because there was too much content that was irrelevant to me. But wouldn't it be great if I could subscribe to only the news items from the BBC that matched the topics I specified? I could enter "Premier league football" as a topic, or I could even narrow it down to my favourite team "Manchester United".

I would like to be able to subscribe to information that currently interests me. For example I am interested in the "two-way web". I can subscribe to personal weblogs that I know will discuss that topic from time to time. But how much more efficient to simply enter the phrase "two-way web" into my RSS aggregator and have it scour the Web, finding and delivering articles about the two-way web. It would be like entering a search into Google - but because this is RSS it is an ongoing, automated delivery of information to me.

There is also an increased chance that I will find more gold nugget articles, by writers I've never heard of. RSS topic feeds may go some way to addressing the A-List blogger problem, whereby a small percentage of bloggers get a disproportionately large amount of hits. This is due to what's called a power law in network theory - a few hubs in a network are immensely more popular than the majority of hubs. Power laws in fact define many things such as the movie industry and the music scene. The World Wide Web itself is a prime example of a power law in motion. A tiny number of "hubs" like Google and Yahoo get a vast number of visits every day. But the Web is made up of millions of pages, most of which are hardly ever visited. (ps check out this Google search query for an ironic example of power laws on the Web - webloggers are the top 3 search results!).

RSS topic feeds will still more likely pick up items from popular bloggers, but at least there is a chance the rest of us will have an article or two "subscribed" to via a topic request.

I want to finish by mentioning a couple of interesting projects that are moving us closer towards a topic subscription model for RSS.

One such project is ENT - which stands for "Easy News Topics". ENT is a module of RSS2.0 and the goal is to "enable a new generation of aggregator applications to be written. These aggregators will allow people to filter items they do not wish to see, prioritize those about things they are interested in and recombine items into new feeds." ENT relies on RSS publishers entering new tag data, in particular the tags 'cloud' (a URI source which describes the topics) and 'topic' (a "metadata item"). There are issues with this "self-categorization" - reliability of data, differences in how people interpret words and phrases, etc. However one of the ENT authors Matt Mowers responded by saying that "ENT could just as easily be used by a categorizer bot that sucked in feeds and annotated them (using heuristics) with topics from it's own cloud." This is an intriguing idea - an automated Yahoo of the RSS world?

Another new RSS app that gathers information by topic instead of author, is Gnews2RSS at VoidStar.com. This application creates RSS feeds on-the-fly for Google news items. You simply enter a topic into a search box, then click the "Create RSS" button. An instant RSS feed is displayed, allowing you to subscribe to it on an ongoing basis using your favourite RSS aggregator.

RSS subscriptions by topics is a step towards the Semantic Web. It gives more customization control to web users and allows all writers to reach a wider audience.