Via Ed Tech Dev, HEML, the Historical Event Event Markup and Linking project, looks like a really interesting concept. It defines an XML format for marking up historical events, along with tools based on Java and XSLT that can convert Heml data in to SVG timelines and other useful representations.
Consider, for instance, twelve diaries or memoirs, each a different view of the Siege of Sarajevo in 1994 and published on the web. They would include entries about events such as the stationing of troops or the evacuation of a certain region on such-and-such a day. If a standard form of mark-up were used to tag the text that recorded these events and their date and location, a computer could collect this information and associate it with the document. It would then be possible to search for descriptions of events on a certain day, or in a certain region or both, and retrieve references to the proper section of the pertinent memoir or memoirs.