The present invention provides increased processing efficiency for service of performing predetermined processes on document data through cooperation among the processes over a network. If an error exists during document input in an input plug-in element before a start of rule-based processing, when documents are captured from the input plug-in element, contents of the error are stored in an error history memory, and documents normally inputted are subjected to processing of processing plug-in and output plug-in elements according to the rule. Also when an error occurs during the rule-based processing, the contents of the error are stored in the error history memory, and the rule-based processing is continued for normal documents. Error histories are referred to, and if an error exists, the error contents are reported on the basis of the error histories.