@evan A prospective search compares each member of a sequence of one or more documents to a previously indexed set of one or more queries. In such a system a query asks: "Tell me whenever!" Because each query looks to the future, the queries are "prospective." Many notification systems rely on prospective search. Similarly, much of the internal operation of SocialWeb systems can be modeled as prospective searches. (i.e. copy post to my feed "whenever" I am mentioned in it.)
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