Relational Database Management Systems are currently suggested to be used as a base for document retrieval systems. This is because commercially available relational DBMSs provide effective tools for managing databases and, especially, the underlying relational model supports ad hoc queries which are characteristic of document retrieval systems. When SQL is directly used for ad hoc queries navigation through the underlying database scheme has to be provided by the enquirer, which could be very difficult. This article presents the achievable simplifications when document retrieval systems will be based on the universal relation model. When the search condition of a query is too fuzzy, the cardinality of the answer set may become very large. Some retrieval systems thus provide the capability of “refining” answer sets; this allows referring to an existing answer set when issuing an additional query to reduce the number of qualifying tuples. There are two different methods to refine a given answer set: one method produces a new query based on the predicates of both queries, the other method creates an intermediate answer set based on the new query and provides the refined answer set via suitable set manipulations. The results are in general different. Focusing on queries on universal relation systems, we describe the above problem in more detail and provide criteria under which the above methods produce the same result.