The delivery ratio of r (which is a fraction between 0 and 1) partitions a stream of documents into a section of top scoring r-fraction of documents and the remainder. This way a set of successively bigger delivery ratios, r.sub.1, r.sub.2, r.sub.3, . . . sections the stream into tiers. Any given document is assigned to a tier according to how many delivery ratio thresholds it matched or surpassed and how many it failed to reach. This creates a scoring structure which reflects the specificity of the document with respect to a profile in terms of density of relevant documents in the stream. In other words, a document in the k.sup.th tier is such that it failed to be classified in the top r.sub.k ratio of the stream (thus r.sub.k fraction of the stream is more relevant to the given profile than the document under consideration). At the same time this document was classified as being in the top r.sub.k-1 part of the stream. Thus this mechanism defines a score (let's call it .sigma.) for a document depending on how it compares to other documents in the stream when scored against a given profile.