Large scale information retrieval systems need to refine the flow of documents which will receive further fine-grain analysis to those documents with a high potential for relevance to their respective users. This paper reports on research we have conducted into the usefulness of semantic codes from a machine readable dictionary for filtering large sets of incoming documents for their broad subject appropriateness to a topic of interest. The Subject Field Coder produces a summary-level semantic

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... epresentation of a text's contents by tagging each word in the document with the appropriate, disambiguated Subject Field Code (SFC). The within-document SFCs are normalized to produce a vector of the SFCs representing that document's contents. Queries are likewise represented as SFC vectors and then compared to SFC vectors of incoming documents, which are then ranked according to similarity to the query SFC vector. Only those documents whose SFC vectors exhibit a predetermined degree of similarity to the query SFC vector are passed to later system components for more refined representation and matching. The assignment of SFCs is fully automatic, efficient and has been empirically tested as s reasonable approach for ranking documents from a very large incoming flow of documents. We report details of the implementation, as well as results of an empirical testing of the Subject Field Coder on fifty queries.