XML on it's own doesn't rewrite the internet and put your website on top. The whole internet has gone xml mad, in some cases placing the importance of XML over human-friendly html!

In addition to our favourite topic, RSS, which is used to share data with other websites, blogs and users (yes, real people), XML is a standard for sharing structured data. It can be likened to a comma separated variable (CSV) file or an Excel (or other) spreadsheet. Like these formats, an XML file could contain data - analagous to the number entered in a cell - which could be contained within a hierachy of tags - comparable to rows, columns, worksheets.

Just as you can't import one company's custom accounting sheet into another's at the click of a button, you cannot import one xml file into another without using a common format. As such, sub-standards such as RSS 2.0, RSS 0.91 used for content syndication and ROR used to catalogue websites for search engines, are required.

One advantage of XML is that the structure and labels of the data are described within the data itself. This means that even if the data is not instantly understood, it may be simpler to work out how to map XML data into your program than a "bare bones" data file.

Also, unike a CSV file, XML is not read blindly, but parsed by element. In English, this means that if certain fields are not included in the XML file they can be safely ignored and the data that is present is read. This again links back to the fact that each element is labelled.

It makes great sense for RSS feeds to be added to news search engines and blog directories so that individual articles or blogs are indexed within the search. Another reason why RSS works so well is that it contains a data about when the content is published, thereby keeping websites current.

Google have recently started (yet) another new service called Google Base, that allows webmasters to submit pretty much any structured data. Is this too open ended and mindblowing? Well, it isn't too dissimilar to what the ROR movement are doing - and the format that they put the data into at Google isn't too much different either - see official ROR blog

More about XML and Search engines using XML soon.