1. A computer-implemented method of processing a plurality of input streams of data using a plurality of continuous queries, the method comprising: processing the plurality of input streams in a computer, by executing thereon the plurality of continuous queries based on a global plan; during said processing, receiving a new continuous query to be executed; during said processing, preparing an additional plan for execution of the new continuous query independent of the global plan; during said processing, traversing the additional plan in a bottom up manner, to select therefrom a current node; during said processing, checking if an operator at the current node is equivalent to any operator in a plurality of operators in the global plan; wherein two operators that perform identical functions with identical inputs are determined by said checking to be equivalent; if said checking finds no equivalent, modifying the global plan by adding thereto said operator at the current node to obtain a modified plan during said processing; if said checking finds equivalence, and if said operator at the current node outputs a relation, propagating from said operator a current state of said relation to a new operator in said new continuous query prior to execution of the new continuous query; returning to said traversing with the modified plan as the global plan, unless the current node is a root of the additional plan; altering said processing, to cause execution of the new continuous query in addition to said plurality of continuous queries, based on the modified plan; and outputting from said computer, a stream generated based at least partially on processing of said data by executing the new continuous query.