Time period directories: a metadata infrastructure for placing events in temporal and geographic context

Metadata is ordinarily used to describe documents, but it can also constitute a form of infrastructure for access to networked resources and for traversal of those resources. One problematic area for access to digital library resources has been the search for time periods or events. If there is a capability to search for time, it is usually a date search - a standardized and precise form but unfortunately rarely used in common chronological expressions. For example, a user interested in the "Vietnam war", "Clinton Administration" or the "Elizabethan Period" must either know the corresponding dates, or rely on simple keyword matching for those period names. We consider the ability to interpret user statements of periods or eras as ranges of dates and to associate them with particular locations an important feature of an information system. This paper describes the Time Period Directory, a metadata infrastructure for named time periods linking them with their geographic location as well as a canonical time period range.