File format conversion method and file system, information processing system, electronic commerce system using the method

The correspondence between originating file (130), conversion program (103) and destination file (131), is determined. One of the files is designated based on the issue of file input/output application program interface (API) entered by user. The format of originating file is converted into format of destination file, by executing the corresponded conversion program using as a trigger the file operation designated by the user. Independent claims are also included for the following: (1) personal computer; (2) server computer; (3) retrieval server computer; and (4) electronic commerce transaction system. In order to perform format conversion between the formats of a plurality of files without any work by a user, a file system (100) stores a relation between a conversion originating file (130) and a conversion destination file (131), and synchronously with an issue of a file operation API, the format conversion processes are executed. A user performs only the tasks essential for an application, without taking into consideration various necessary format conversions (either one-step or multi-step). During the user task, it is not necessary to designate a conversion originating file and a timing of format conversion. A user can use always a latest conversion destination file.