The Domesday Book, the oldest and most famous public record, was based on the 1086 great survey of England.

There would be nothing like it in England again until the censuses of the 19th century.

But for nearly 1000 years it has been inaccessible to most people and difficult to understand. There are costly CD-Rom translations, and the UK's National Archives provides online searches, but Palmer has coded and tagged terms so they can be automatically retrieved and analysed.

His software makes it possible to isolate certain variables and conduct several searches at once. The results can be displayed as a map, table or translated text, or as a combination of formats.

The three-year project was funded by a £250,000 ($617, 000) grant from the Arts and Humanities Research Council.

Palmer, who worked on the project with his son, Matt, said: "My interest in Domesday began in about 1980 as a teaching project ... It developed into a research interest for the 900th anniversary in 1986, but computers weren't powerful enough then."

Written in Latin, the Domesday Book lists places, landowners and tenants, tax assessments, cultivated land, numbers of oxen and plough teams, property values, legal claims, illegal activity and social classes such as freemen, villeins, smallholders, cottagers, slaves, priests and burgesses.

Palmer said: "No English medieval historian can ignore the book because it's such an important source for social and economic medieval history."