In this paper we give an overview of the UDK project, an international software engineering effort to facilitate access to environmental data. The UDK (Environmental Data Catalogue) is a metainformation system and navigation tool that documents collections of environmental data from the government and other sources. Potential users of the system include government agencies, industry, as well as the general public. Technically, the UDK is based on a three-way object model that distinguishes between environmental objects, environmental data objects, and UDK (meta) objects. Each (real-world) environmental object is described by a collection of environmental data objects. Each environmental data object is in turn associated with exactly one UDK object that specifies its format and contents. UDK objects are classified in accordance with an object-oriented inheritance hierarchy. They may be connected in a hypertext fashion to represent semantic associations, such as maintenance responsibilities and aggregation relationships. In January 1995, a first version of the UDK was made available in Austria; most German states will follow shortly. We also expect a prototypical version of the UDK to be available on the Worl
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