13. A computer-readable storage medium retrievably storing a computer-executable program for causing a computer to process a flow processing document, the computer program comprising steps of: extracting, from a first flow description document, a first description which specifies services to be invoked by the first flow description document, and extracting, from a second flow description document, a second description which specifies services to be invoked by the second flow description document; detecting a common part between the first description of the first flow description document and the second description of the second flow description document, wherein services specified by the first description extracted from the first flow description document include one or more services among services specified by the second description extracted from the second flow description document; and rewriting the common part in the second flow description document into a reference to the common part in the first flow description document, wherein the reference includes identification information of the first flow description document, and information which specifies a start tag and end tag of the common part.
13. A computer-readable storage medium retrievably storing a computer-executable program for causing a computer to process a flow processing document, the computer program comprising steps of: extracting, from a first flow description document, a first description which specifies services to be invoked by the first flow description document, and extracting, from a second flow description document, a second description which specifies services to be invoked by the second flow description document; detecting a common part between the first description of the first flow description document and the second description of the second flow description document, wherein services specified by the first description extracted from the first flow description document include one or more services among services specified by the second description extracted from the second flow description document; and rewriting the common part in the second flow description document into a reference to the common part in the first flow description document, wherein the reference includes identification information of the first flow description document, and information which specifies a start tag and end tag of the common part. 16. The medium according to claim 13 , wherein in the rewriting step, execution of the common part in the first flow description document is designated based on the reference when executing the second flow description document.