The invention notably relates to a computer-implemented method, performed by a server storing an index of a search engine, for sending, to a client, the URLs of pages of a Web corpus that relates to a theme. The method comprises receiving, from the client, a structured query that corresponds to the theme, the structured query consisting of a disjunction of at least one keyword; determining in the index the group that consists of the URLs of all pages that match the query; and sending to the client the URLs of the group as a stream.Such a method improves the building of a thematic Web corpus.