A system and method for dynamically building applications for stream processing includes providing processing elements with a flow specification describing each input and a stream description describing each output such that the flow specification indicates a stream or streams which are to be received based on processing information and the stream descriptions indicate the processing information. Processing elements that can be reused are identified by determining equivalence between the processing elements. Processing elements that are new and are not reusable are instantiated in a flow graph. An application is dynamically composed, using the instantiated processing elements by routing available streams to the instantiated processing elements in accordance with the flow specifications.