Some embodiments provide a novel method for collecting and reporting attributes of data flows associated with machines executing on a plurality of host computers to an analysis appliance. Some embodiments collect, each time a request for a new data message flow is initiated, a set of contextual attributes (i.e., context data) associated with the requested new data message flow. The method, in some embodiments, generates a correlation data set and provides the correlation data set to be included in flow data regarding the requested data message flow to be used by the analysis appliance to correlate context data and flow data received as separate data sets from multiple host computers.