The protocol should also be able to asynchronously provide the browser-based client with data. Occasionally, the layout of a Web site changes, too, and sometimes even the schema of the database from which the Web sites obtains its data may change. Presentation of live data is a potentially difficult task. By live data we mean data that may change while the user is viewing a set of query results. Examples of live data include news, stock quotes, airline fares and seat availability.
Live data are frequently numerical or computable.
The user should be able to interact with this data. If a user's preferences are known, then the schema may be further customized based on the user's previous explorations and on the explorations of other users with similar profiles. An anonymous user is one whose demographic profile is not known to the query engine. One approach to tailor query results to anonymous individuals is to have them specify a set of preferences each time they submit a query. The preferences may be used to relax and refine the query as well as to prune and rank results.