Semantic Web Calendaring: RDF Calendar, hCalendar, and GRDDL

The Web not only provides a neutral answer questions about word processor formats, operating systems, and networking technologies, but it integrates individual documents into a whole, so that if information is already in the Web somewhere, you can just link to it. HTML is feature-poor when compared to other document formats, but the integration benefits of linking outweigh the costs.

This works pretty well for documents. If you're asked to provide a document to people that use different kinds of computers, you can just put it on the Web in HTML and they can all read it. But the integration problem is still there for data. When a soccer coach distributes a schedule for the season, each of the players has to re-key the information for their calendar system if they want their computer to help them manage conflicts. When an airline sends itineraries, each passenger manually processes them.

The problem is addressed at least in part by an Internet standard for calendar data, iCalendar[RFC2554]. But it's not clear that iCalendar provides sufficient integration benefits to outweigh the cost of migrating to open systems from more mature closed calendaring systems.

The RDF Calendar vocabulary is the result of a test-driven Semantic Web vocabulary development effort. hCalendar is an emerging microformat standard. GRDDL lets you store RDF data in XHTML documents, such as hCalendar documents. This RDF data cam be mixed with social networking data (FOAF), syndicated content (RSS), multimedia metadata (dublin core, musicbrainz) and more, and promises the sort of linking and integration benefit that made HTML the leading choice among document formats.