4. A processing method performed by a processing apparatus having a processing unit, the processing method comprising: inputting a first process description document; performing a service, by the processing unit, 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; generating, by the processing unit, a second process description document including the first and fourth description parts by deleting, from the first process description document, second and third description parts; and sending the second process description document to the next processing apparatus described in the deleted second description part.
6. The processing method according to claim 4 , wherein the first and second process description documents include a description part describing a conversion from at least one variable in which a result of the service is stored into at least one variable used for the processing apparatus to be called.