1. A data display system including a client computer and a server connected through a network, comprising: a first memory storing a plurality of data definition files of a first type defining contents of data to be displayed on said client computer; a second memory storing a data definition file defining, as data, file names of said data definition files of the first type; a third memory storing a style definition file, defining a style for displaying said data definition file, and switching a file to be displayed among said plurality of data definition files of the first type by using said data definition file of the second type; and a display displaying data on the client computer using the files stored in said first, second and third memories.