Follow-up work at Stanford by F. Corella et al. showed that cooperative responses are useful in a setting that uses formal language rather than natural language for man-machine interaction, such as a bibliographic database. A cooperative response to a formal-language query that does not produce results may suggest as follow-up queries minimal generalizations of the query that do produce results, and may also point out maximal generalizations of the query that do not produce results as explanations of the failure of the original query.
Since then, further academic work has shown how cooperative responses can be provided in a variety of other formal settings. Outside of academia, implementors of database systems have also adapted or independently discovered the concept. In particular, the database at ClinicalTrials.gov lists miminal generalizations of queries that produce results in response to certain queries that produce zero results.
A Web search almost always has results. This is because there is much "garbage" on the Web, including many pages with huge collections of unrelated words. However, zero-results can be encountered when searches are restricted to a particular Web site, and cooperative responses are then very useful. We believe that Noflail Search is the first Web search engine to provide cooperative responses.
When cooperative responses are available, users may modify their search strategy to take advantage of them by issuing queries that produce zero results on purpose.