14. The computer-readable medium of claim 12 wherein said instructions further comprise instructions for executing the step of determining, on the basis of said absolute-relevance score of said newly-received document and said first collective absolute relevance, whether to replace said first set of training data by a second set of training data formed by adding said newly-received document to said first set of training data.
14. The computer-readable medium of claim 12 wherein said instructions further comprise instructions for executing the step of determining, on the basis of said absolute-relevance score of said newly-received document and said first collective absolute relevance, whether to replace said first set of training data by a second set of training data formed by adding said newly-received document to said first set of training data. 16. The computer-readable medium of claim 14 wherein said instructions for executing said step of determining whether to replace said first set of training data further comprise instructions for executing the steps of: evaluating an absolute relevance for said newly-received document; selecting, on the basis of said relative relevance threshold, a first training document to be a least-relevant document; determining whether said newly-received document has a higher absolute relevance score than said least-relevant document; if said newly-received document has a higher absolute relevance score than said least-relevant document, replacing said first set of training data with a second set of training data formed by incorporating said newly-received document into said plurality of training documents; and selecting, on the basis of said relative-relevance threshold, a second training document from said second set of training data to be said least-relevant document, said second training document having a higher absolute relevance score than said first training document; whereby successive newly-received documents require progressively higher absolute relevance scores to surpass said relative relevance threshold.