Mining dates from historical documents

The essential quality of information in a digital library is accessibility. Full text search is not enough for some collections, more can be done. Historical collections, for example, contain dates and it would be useful to historians to be able to search by them. However, these dates may occur anywhere within the text of historical documents, and to be searchd they must be extracted from the documents and integrated into the collection index. Doing this manually is very expensive, and described here is a system to do it automatically. This system was implemented within the Greenstone framework used by the New Zealand Digital Library, and involved the use of some carefully designed heuristics.