terms (e.g. trade nomenclatures), so they had to be presented to the user for easy selection. Each time-series is described by three terms, one for each of the categories topic (e.g. building permits), product (e.g. residential buildings) and region (e.g. Germany). A valid query consists of at least one term from each category per database. Terms within a category are combined by the Boolean' OR operator, the categories are combined with AND (figure 1). This restricted Boolean' search logic had to be hidden from the user by the user interface.
Task analysis with market researchers showed that they have different knowledge of the trade nomenclatures which were used to index the data. It was not generally clear which one to use for searching in a specific database. So the interface had to make explicit, which terms to use in a certain context. The typical information needs here cover multiple databases at the same time (e.g. to produce some graphics or to calculate trends).
A hierarchical approach - with the selection of one database in the first step and the presentation of the relevant lists of terms in a second step - was not applicable because the users didn't like to split their information needs into a sequence of queries. A single screen, containing all available lists all of the time, was rejected because of information overload when retrieving data from just one database and missing hints which terms to combine in a query.
The proposed solution is based on dynamic spatial layout of window elements along with the propagation of information between them. The first is used to dynamically adapt information density within context and to enforce semantically correct queries. The second makes user input and status information available at different locations, to allow for corrections without going back to where the input was made. A related approach to dynamic spatial layout can be found in Kandogan/ Shneiderman ( 1996).
Figure 2 displays the ELVIRA query interface to time-series data. The lower part of the window contains the lists of search terms with the categories topic, product and region arranged in three columns. The category region his hidden by default to provide additional space for the list of products and because specifying a region is often the last step in completing the query. The top of the