1. Library Literature (New York: H.W. Wilson) See the 1993 volume at page 954 and the 1994 volume at page 785.
2. ESRI White Paper series;Environmental Systems Research Institute, Inc.,1994
3. The Alexandria Project: Towards a Distributed Digital Library with Comprehensive Services for Images and Spatially-Referenced Information,1994
4. International GIS Sourcebook,1991