The goal of most hypermedia systems is to open up complex information spaces through the use of associative networks of nodes containing texts. images. and acoustic signals. The power of such information systems can be considerably enhanced by the integration of knowledge representation. We illustrate this claim with an example hypermedia information system about the oldest existing globe of the earth whose creation was initiated by Martin Behaim in 1492. Displaying the pre-columbian image of the earth, the Behaim globe is a cartographical masterpiece of German humanism in the Renaissance age; nowadays the globe is exhibited in the Germanisches Nationalmuseum in Nuremberg.From the user viewpoint, our hypermedia information system offers two paths for information access, one through a graphical visualization component which can produce images of the globe from any desired viewpoint, and a graphical query interface to a hypermedia network which provides structured information units consisting of texts and images. These units contain descriptions of the different globe regions and their map image, various readings of its numerous inscriptions, comments on the texts and miniatures on the globe, images of contemporary globes and maps, a comprehensive record - in part on-line accessible - of important scientific publications on the globe, and cultural and historical background information. Particular attentention is paid to the broad variety of relations between images and texts.
For the information system. a new distributed software architecture based on WWW technology has been specified and implemented. The server component consists of the system kernel and several server components, to which the kernel dispatches upon request. Among the components are an object-oriented database system with a specific query component (via CLOS, the Common LISP Object System and Allegro/Object Store), an image database and preprocessing component, and a component for generating hypertext (HTML) pages from database contents. The object-oriented database system holds all data objects describing the globe, its parts, and background information. as well as descriptors for all kinds of media data. Immutable image data and text files (scanned documents) are kept separately, but are accessible only through these descriptors.
The query interface as well as local image processing operations are implemented as Java applets running locally with a WWW-Browser. To display birdeye views on the globe from the image database, which contains wavelet encoded high resolution images, a new visualization component based on OpenGL has been implemented. With sufficient hardware support, real time animation is possible. The structure of the information space is described in an object-centered representation which is -due to the use of CLOS - identical with the database schema. In modelling we followed the goal to define an open terminological hierarchy of sufficient generality for historical cartography in general. In particular, we are currently working on a spatial reasoning component operating on representations of topographical objects and some general reasoning operations - like consistency, classification, etc. -through an interface to a description logic system.