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No matter how big the HT corpus is, or how powerful the existing algorithms are, if the existing (corpus + algorithms) do not meet the needs of the specific problem that the user is trying to solve, then the user will not use the resources. Often, people come to librarians with their own texts (such as EEBO, ECHO, the Old Bailey text corpus, etc., and describe the problem and request an algorithm to be written to do the analysis that they are trying to do. Nowadays, even undergraduates come with quite complex tasks that they are trying to do.
Sometimes, the text data set that the user is interested in using, are government documents that get set out periodically — all the articles put out within a certain time period.