A large number of studies have investigated the query logs of Web search engines, but there is a lack of analogous studies for multimedia database management systems (MDBMSs) used by professional searchers. In this paper we perform an extensive analysis of the query logs of the RAI multimedia catalogue, both at the query level and at the session level. Based on the observation that a large proportion of the queries returned zero or, conversely, too many hits, we identified three query reformulation strategies to reduce or enlarge the set of results. Our study indicates that the desire of controlling the amount of output may have a relatively limited (moderate-to-little) impact on the user's behavior, while at the same time some counter-intuitive findings suggest a suboptimal utilization of the system. The findings are useful for MDBMS developers and for trainers of professional searchers to improve the performance of interactive searches, and for researchers to conduct further work.