Continuous queries over data streams may suffer from blocking operations and/or unbound wait, which may delay answers 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 paper we present a semantics for queries and corresponding answers that covers such hypothetical answers, together with an online algorithm for updating the set of facts that are consistent with the currently available information.

翻译：数据流上的连续查询可能遭受阻塞操作和/或无限等待的影响，这可能导致答案延迟直到某些相关输入通过数据流到达。这些延迟可能使得答案在到达时对用户而言已经过时，而用户有时必须在没有任何帮助的情况下做出决策。因此，提供假设性答案——“根据当前信息，X可能在时间t变为真”——而非完全不提供信息可能是有用的。本文提出了一种涵盖此类假设性答案的查询及相应答案的语义，同时给出了一种在线算法，用于更新与当前可用信息一致的事实集合。