1. A processing apparatus comprising: a computer readable memory; an input unit configured to input a first process description document; and a processing unit configured to store a program in the computer readable memory and execute the program, wherein the processing unit is configured to perform a service in accordance with a procedure written in the first process description document including first, second, third and fourth description parts, the first description part describing a receiving processing for receiving data from a client via a network and a service processing for performing the service, the second description part describing a call processing for calling a second processing apparatus which is connected to the network and provides a second web service, the third description part describing a conversion from a variable used by the second processing apparatus to a variable used by a third processing apparatus, and the fourth description part describing a call processing for calling the third processing apparatus which is connected to the network and provides a third web service, to generate a second process description document including the first and fourth description parts by deleting, from the first process description document, the second and third description parts, and to send the second process description document and result of the service to the second processing apparatus described in the deleted second description part.