Browsing is an interactive and exploratory process for finding information in a digital library that has advantages over search term queries in many situations. Some browsers display a concept space as a node-link graph diagram, but this can look chaotic for a graph of moderate complexity. The approach taken in this paper is to suppress some of the interrelationships (links) and order the concept space as a tree by some `natural' hierarchy. The user can then explore hidden interrelationships by dynamically interacting with the system. We demonstrate the usefulness of browsing a hierarchy via this method in a prototype called MeSH-BROWSE, a system for browsing terms from the NLM Medical Subject Headings tree. It displays a node-link tree diagram of the con-cept space and reveals hidden interrelationships when a node is clicked on by triggering related nodes scattered about the tree to become highlighted. In this paper we describe MeSHBROWSE, discuss semantic and algorithmic issues involved with it, and discuss its implications for further research.
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