& Prümper 1998). The current paradigm for user interfaces is that of direct manipulation ( Shneiderman 1997). Visual tools developed according to this paradigm, e.g. FilmFinder ( Ahlberg & Shneiderman 1994), a user interface for a movie database, support the memory recognition technique very well, but offer no support for the recall technique. Beside this, only a flat hierarchy is supported.
The example knowledge domain is that of all reports in the Business Information Warehouse of the SAP AG, Walldorf. Accumulated information e.g. revenue information by customer is normally shown in reports. The set of these reports can be structurised into three layers: a layer of report attributes (e.g. fields), one of the report hierarchy based on business terms (reporting tree) and another layer that assigns one report to a so-called info-cube which contains a set of related fields.
Based on the theoretical arguments and a survey among more than 40 SAP R/3 report users, requirements for a search tool were set up. These include the support of searching and browsing, an incremental search approach, the abilities to show different levels of detail and to change the hierarchy level, full text search capabilties, the ability also to enrich the query and to have a preview of the selected object before selection. The task-knowledge-structure model (TKS) was used to identify the tasks for finding reports and to structure and split the functions between humans and the computer ( Johnson & Johnson 1998). The human tasks were transformed into a psychological act diagram that led finally to the dialogue model of the search system. The model is described in figure 1, using generalised transition networks (GTN) ( Mittermayer & Haubner 1987).
The dynamic dialogue model consists of the following steps: full text search, searching and browsing hierarchies and fields, searching and browsing report details including a preview and starting the resulting report. In the beginning, the user has to narrow the query by entering keywords. In the next steps, browsing is also possible by adding displayed objects to the query. Different hierarchy structures are differently visualised to reduce complexity. Additionally, the attributes of a report selected with the mouse are displayed, and could optionally be added to the query. If the number of retrieved reports is low, all details including a preview are shown, assuming that the user is very near to his desired report and needs every information item to choose among possibly similar reports. Every step's output is the input for the next step and on every step both narrowing and broadening the query is possible.