  An operationalistic scheme, called Melucci metaphor, is suggested
representing Information Retrieval as physical measurements with beam of
particles playing the role of the flow of retrieved documents. The
possibilities of query expansion by extra term are studied from this
perspective, when the particles-`docuscles' are assumed to be of classical or
quantum nature. It is shown that in both cases the choice of an extra term
based on Bayesian belief revision is still valid on the qualitative level for
boosting the relevance of the retrieved documents.
