Next: Comparison of Two ``Document Similarity Search Engines'' . ... A drawback of the current document representation scheme in the ADS abstract service is its heterogeneous subject indexing. ... Using lexical similarity alone, one out of six ADS descriptors can be automatically mapped to some other descriptor. ... Researchers at the University of Illinois were invited to investigate methods of merging the indexing languages in use in ADS, and any other methods of dealing with the heterogeneity. ...