Representing document lengths with identifiers

The length of each indexed document is needed by most common text retrieval scoring functions to rank it with respect to the current query. For efficiency purposes information retrieval systems maintain this information in the main memory. This paper proposes a novel strategy to encode the length of each document directly in the document identifier, thus reducing main memory demand. The technique is based on a simple document identifier assignment method and a function allowing the emph{approximate} length of each indexed document to be computed analytically. The paper discusses the implication of the adoption of the proposed technique, and the encouraging results of the experiments conducted with the 2009 TREC Web Track dataset.