Hypothetical Answers to Continuous Queries Over Data Streams

Answers to continuous queries over data streams are often delayed until some relevant input arrives through the data stream. These delays may turn answers when they arrive, obsolete to users who sometimes have to make decisions with no help whatsoever. Therefore, it can be useful to provide hypothetical answers—“given the current information, it is possible that X will become true at time t”—instead of no information at all. In this work, we present a semantics for queries and corresponding answers that cover such hypothetical answers, together with an incremental online algorithm for updating the set of facts that are consistent with the currently available information. Our framework also works in a language supporting negation.