1. An image processing apparatus for outputting a document including a data group containing a plurality of data items, comprising: a storing part configured to store document definition data in which a plurality of document kind data indicating contents of output documents are defined in correspondence with output pattern data, the output pattern data including output method data and output condition data; a structured data fabricating part configured to fabricate structured data including the data group according to the document kind data, the structured data being independent from an output method and an output condition of the document, the structured data fabricating part including a plurality of logical document fabricating modules corresponding to the plurality of document kind data; an image data fabricating part configured to fabricate image data of the document according to the structured data; an identifying part configured to identify target document definition data among the document definition data that correspond to designated document kind data; an outputting part configured to output the image data according to the output pattern data corresponding to the document kind data defined in the target document definition data; and a document function providing module configured to be installed in and uninstalled from the image processing apparatus, the document function providing module configured to register additional document definition data, in which additional document kind data are defined, and an additional logical document fabricating module that corresponds to the additional document kind data.