The original VT100 interface to Okapi uses a character-based display --- users press cursor or character keys to navigate, and information is presented a screenful at a time. The system attempts to provide the benefits of query expansion without exposing the complexity of the term extraction process. Once users have selected some relevant documents, they are offered automatic query expansion with the message:
Type M to see more documents like the ones you have chosen.
At this point, terms from relevant documents are extracted to produce a completely new query, and a new search is undertaken leading to the presentation of a new hit-list.
Within the limits of a character-based interface, the VT100 system proved very successful [4]. First time users experienced no difficulties in carrying out searches and were just as likely to use the query expansion facility as regular users. However, there were some problems. Although expanded searching identified more relevant items in 50% of the occasions when it occurred, only a third of the users chose to do it. Interviews with users indicated that some had not taken up the option because they did not wish to undertake exhaustive searches, or to find more items if the initial result was satisfactory. But there were also users who did not know what to expect when they chose the ``More'' option, and a few who simply did not notice the message at the bottom of the screen.
Obviously not all users do need to search the database exhaustively, but it was considered necessary to address some of the other points raised. It was suggested that users could be given more control over query re-formulation via interactive query expansion and that a graphical user interface, exploiting multiple windows, colours and fonts, might be a way to make the ``More'' option and other system facilities visible for those users who could benefit from them. This was the focus of the project described in the next section.