Abstract: A method for searching a collection of documents, comprising: providing a document; providing a keyword associated with that document; certifying the relevance of the keyword to that document; and making the certified keyword available to a search engine. A database system comprising: a plurality of documents; at least one keyword associated with each of the plurality of documents, wherein the keyword has been certified for relevance to its associated document; and a search engine for searching the certified keywords. A database system comprising: a plurality of documents; a set of keyword tags, each of which is associated with an indication of either the content of a document, or its relevance to certain search engine queries, or both; keyword tags associated with each of the plurality of documents, wherein the tag has been associated with the document according to the preference of a user; and making the tags available to a search engine.