1. A document processing system comprising: a storage unit constructed to store plural items of document data, plural items of metadata pertaining to a content of each item of document data, and relation information representing relations between the plural items of document data; an input unit constructed to input image data; a specifying unit constructed to specify document data related to the image data input by the input unit among the plural items of document data stored in the storage unit; and a control unit constructed to control the storage unit to store relation information representing a relation between the image data input by the input unit and the related document data specified by the specifying unit, and to store metadata of the related document data specified by the specifying unit as metadata of the image data input by the input unit, wherein the storage unit is controlled to store the metadata of the related document data if a similarity of the image data input by the input unit and the related document data specified by the specifying unit is equal to or higher than a predetermined threshold, wherein the metadata of the related document data specified by the specifying unit is stored with a certainty factor based on the similarity, and wherein the certainty factor is calculated according to a predetermined algorithm based on a relation type and type-specific degree of relation.
1. A document processing system comprising: a storage unit constructed to store plural items of document data, plural items of metadata pertaining to a content of each item of document data, and relation information representing relations between the plural items of document data; an input unit constructed to input image data; a specifying unit constructed to specify document data related to the image data input by the input unit among the plural items of document data stored in the storage unit; and a control unit constructed to control the storage unit to store relation information representing a relation between the image data input by the input unit and the related document data specified by the specifying unit, and to store metadata of the related document data specified by the specifying unit as metadata of the image data input by the input unit, wherein the storage unit is controlled to store the metadata of the related document data if a similarity of the image data input by the input unit and the related document data specified by the specifying unit is equal to or higher than a predetermined threshold, wherein the metadata of the related document data specified by the specifying unit is stored with a certainty factor based on the similarity, and wherein the certainty factor is calculated according to a predetermined algorithm based on a relation type and type-specific degree of relation. 5. The system according to claim 1 , further comprising a decision unit constructed to determine document ranks of the plural items of document data stored in the storage unit, based on the relation information.