 To evaluate a continuous query, one can simply reevaluate the query over newly arrived tuples, and append the new tuples to the existing result set.More formally, let "A(Q, t)" be the answer set of a continuous query "Q" at time t, τ be the current time, and 0 the start time.Then, if Q is monotonic, its result set at time τ is

In contrast, non-montonic queries have the following answer semantics