1. A method of operating an apparatus, including instructions, the method comprising: (a) receiving a document which includes: (i) an internal structure including: (A) a first element having a first active value; and (B) a second element having a second active value; and (ii) first characteristic information; (b) causing a processor to execute the instructions to diffuse the first active value and the second active value; (c) causing the processor to execute the instructions to, using the diffused first active value and the diffused second active value, extract the first characteristic information having post-diffusion active values larger than pre-set threshold values; (d) causing the processor to execute the instructions to operate with an input device to enable a user to form a plurality of classification items which have second characteristic information; (e) causing the processor to execute the instructions to, using the formed plurality of classification items, prepare a classification model; (f) causing the processor to execute the instructions to determine a degree of interrelation between the extracted first characteristic information and the second characteristic information; (g) causing the processor to execute the instructions to determine whether the determined degree exceeds a threshold value; (h) in response to the determined degree exceeding the threshold value, causing the processor to execute the instructions to, using the prepared classification model, automatically classify the document into one of the formed plurality of classification items; (i) in response to the document being automatically classified, causing the processor to execute the instructions to update the classification model based on the classification of the document, wherein a weight is imparted to each element based on the internal structure of said document; and (j) causing the processor to execute the instructions to extract an element having the weight larger than a pre-set value.