Incremental query expansion based on relevance feedback is a unique feature introduced in the ENQUIRE project. This innovation was a result of the evaluation of other approaches to query expansion functionality and presentation implemented in different interface environments for two previous projects (discussed in the introductory chapter to this report).
The Okapi at City project was concerned with evaluating automatic query expansion in a character-based interface [15,16]. The results demonstrated the basic usefulness of the facility but there was some indication that it would be beneficial if users were allowed to select candidate terms. Although the interface based on a natural language dialogue style was deemed to be intuitive, i.e. easy to use and self explanatory, the system's full functionality was not visible to the user and the selection of terms for query expansion was primarily system-controlled.
The first Okapi GUI project made the query expansion process more interactive by displaying candidate lists of terms for selection by the user [17]. However, operational testing showed that searchers did not fully understand the task in hand. They found it difficult to assess the appropriateness of additional terms, and consequently tended to be highly selective, often choosing only those terms which had been in the original query. The increased cognitive load on the user not only led to a lower up-take of the query expansion facility, but also tended to make it less effective when it was used. The net effect of giving the user more control of the process was to work against the system's capabilities.
The ENQUIRE project addressed the need to consider more carefully the relationship between the underlying term extraction functionality and its presentation at the interface. This led to changes in both. In the first GUI, query construction was presented as a secondary task in the retrieval process which could assist in extending a current search. The extracted terms were shown to the searcher only if he chose the ``extend search'' option. Having chosen the option, users found it difficult to relate the extracted terms to the current pool of relevant items, and even more problematic to anticipate what combination of terms would lead to a desired or improved result.
By contrast the ENQUIRE interface focused on the query from the outset. Once an initial result was produced the searcher's attention was directed at viewing the results, but the working query always remained visible. The system provided immediate feedback whenever relevance judgements had any effect on the working query, by displaying new terms and / or re-ordering existing ones by their adjusted weight. (The colour coding of terms from different sources was also intended to make the composition of the working query apparent.)
The system's dynamic response would not necessarily be noticed every time a change occurred, particularly if the retrieved items were still being viewed and were of interest. But once the results were no longer fruitful, the searcher's attention was more likely to have been drawn back to the query. Moreover the small incremental changes should have made it easier to associate extracted terms with specific documents, motivating searchers to make more subtle modifications of their own. At any one time the user had to deal with a more manageable number of new terms than in the previous GUI. Thus the presentation of the functionality at the interface was more likely to encourage co-operation between the system and the user in query construction.