1. A method for managing a data stream, comprising: receiving a continuous query; generating an iterator-model plan based on the continuous query; adding the continuous query to a shared continuous-query plan by: analyzing the iterator-model plan and generating a plurality of iterator-model subplans by walking the iterator-model plan bottom-up to generate transforms, plan items and qual items based on the iterator-model plan; and for at least one particular iterator-model subplan of the plurality of iterator-model subplans: assigning a continuous-query operator to the particular iterator-model subplan; and adding an adapter as a new leaf node to the particular iterator-model subplan, wherein the adapter is an iterator-model operator configured to fetch one or more processed continuous-query tuples from the continuous-query operator and provide the one or more fetched continuous-query tuples to the particular iterator-model subplan of the adapter; applying the transforms to convert local range variables of the continuous query to global range variables; and based on the plan items and the qual items, modifying the shared continuous-query plan, wherein the plan items refer to one or more new or existing continuous-query operator of the shared continuous-query plan, and wherein the qual items comprise information specific to at least one of qualifiers and predicates; wherein the method is performed by one or more computing devices.