A computer-implemented system for providing a topic-directed search, comprising: a plurality of evergreen indexes for topically-limited subject areas, each evergreen index being an index that remains current with a corpus, each of the subject areas comprising articles of digital information and for each of the evergreen indexes, comprising: a hierarchy of topics; and a fine-grained topic model paired to each of the topics in the topic hierarchy, each of the fine-grained topic models comprising a pattern evaluable against the articles, wherein the pattern identifies such articles matching the fine-grained topic model's topic, that are both electronically-stored in persistent storage; a computer comprising a processor and memory within which code for execution by the processor is stored, comprising: a topic builder that, for each topic in each of the evergreen indexes, maintains a coarse-grained topic model comprising: a characteristic word extractor that extracts characteristic words from the articles identified by the fine-grained topic models of each topic; and a characteristic word scorer that assigns scores to the characteristic words; and a search engine that specifies a topic search comprising search terms, and that evaluates the coarse-grained topic model of each of the topics in the evergreen indexes by matching the search terms and accumulating their scores; and a user interface that visually presents the evergreen indexes comprised of the topics that comprise the coarse-grained topic models having the best scores. a plurality of evergreen indexes for topically-limited subject areas, each evergreen index being an index that remains current with a corpus, each of the subject areas comprising articles of digital information and for each of the evergreen indexes, comprising: a hierarchy of topics; and a fine-grained topic model paired to each of the topics in the topic hierarchy, each of the fine-grained topic models comprising a pattern evaluable against the articles, wherein the pattern identifies such articles matching the fine-grained topic model's topic, that are both electronically-stored in persistent storage; a hierarchy of topics; and a fine-grained topic model paired to each of the topics in the topic hierarchy, each of the fine-grained topic models comprising a pattern evaluable against the articles, wherein the pattern identifies such articles matching the fine-grained topic model's topic, that are both electronically-stored in persistent storage; a computer comprising a processor and memory within which code for execution by the processor is stored, comprising: a topic builder that, for each topic in each of the evergreen indexes, maintains a coarse-grained topic model comprising: a characteristic word extractor that extracts characteristic words from the articles identified by the fine-grained topic models of each topic; and a characteristic word scorer that assigns scores to the characteristic words; and a search engine that specifies a topic search comprising search terms, and that evaluates the coarse-grained topic model of each of the topics in the evergreen indexes by matching the search terms and accumulating their scores; and a topic builder that, for each topic in each of the evergreen indexes, maintains a coarse-grained topic model comprising: a characteristic word extractor that extracts characteristic words from the articles identified by the fine-grained topic models of each topic; and a characteristic word scorer that assigns scores to the characteristic words; and a characteristic word extractor that extracts characteristic words from the articles identified by the fine-grained topic models of each topic; and a characteristic word scorer that assigns scores to the characteristic words; and a search engine that specifies a topic search comprising search terms, and that evaluates the coarse-grained topic model of each of the topics in the evergreen indexes by matching the search terms and accumulating their scores; and a user interface that visually presents the evergreen indexes comprised of the topics that comprise the coarse-grained topic models having the best scores.