1. An event-categorizing subsystem within an event-collection-and-event-processing system that includes one or more computer systems, each of the one or more computers having one or more processors, one or more memories, and one or more mass-storage devices, the event-categorizing subsystem executing operations to: receive a stream of events, each event comprising a set of key/value pairs, the stream of events stored in one or more memories and/or mass-storage devices; apply a seeded global/local-topic Latent Dirichlet Allocation analysis to a subset of events of the stream of events in order to assign each event of the subset of events to one of K different topics, where K is an integer value greater than 1; generate K topic signatures, each topic signature of the K topic signatures corresponding to a topic of the K different topics and being generated using the subset of events assigned to the topic; and for each subsequently received event, computing a set of scores for the received event, each score in the set of scores being generated using a topic signature of the K topic signatures, assigning the received event to a topic based on the computed set of scores, storing, in one of the one or more memories, an indication of the topic to which the event is assigned, and forwarding the event, including the indication of the topic to which the event is assigned, to an event-processing subsystem.