1. A method for providing an output data stream in a network system, the method comprising: receiving a request for a desired output data stream; identifying at least one input data stream on the basis of the desired output data stream; identifying at least one relationship between the at least one identified input data stream and the desired output data stream; determining at least one operator on a basis of the at least one identified relationship; creating a query for generating an output data stream corresponding to the desired output data stream by applying the at least one operator to the at least one identified input data stream; the at least one input data stream being identified by referring to a stored mapping between a data information included in the received request and at least one type of data included in a stored data schema, the data schema associating each type of data with at least one input data stream; and the at least one relationship being identified by referring to the stored mapping.