In a networked information system, there are three major obstacles facing users in a querying process: slow network performance, large data volume and data complexity. In order to overcome these obstacles, we propose a two-phase approach to query form ulation: Query Preview and Query Refinement. In the Query Preview phase, users formulate an initial query by selecting desired attribute values. The volume of matching data sets is shown graphically on preview bars which aid users to rapidly eliminate undesired data sets, and focus on a manageable number of relevant data sets. Query previews also prevent wasted steps by eliminating zero-hit queries. When the estimated number of data sets is low enough, users submit the initial query to the network, which returns the metadata of the data sets for the Query Refinement phase. Using this approach, we developed dynamic query user interfaces allowing users to formulate their queries using direct manipulation in an exploratory manner across a networked environment. (Also cross-referenced as CAR-TR-788 (Also cross-referenced as ISR-TR-95-90