A data processing apparatus that requests an external apparatus to execute apart of sequential processing, receives a control request from the external apparatus, and executes the sequential processing in response to the control request that reflects an execution result of the part of the sequential processing performed by the external apparatus, includes a generation unit configured to generate identification information that can be used to determine whether a processing execution request sent to the external apparatus is output via an operation unit of the data processing apparatus, a storage unit configured to store the identification information generated by the generation unit in a storage medium, a transmission unit configured to transmit the identification information generated by the generation unit to the external apparatus, a reception unit configured to receive the control request from the external apparatus.