5. The non-transitory computer-readable recording medium according to claim 1 , wherein, the character string associated with each of the logical elements in the logical structure model includes a designation of the logical element and an actual expression of the logical element, and a limit condition for an attribute of the character string is established to the actual expression.
5. The non-transitory computer-readable recording medium according to claim 1 , wherein, the character string associated with each of the logical elements in the logical structure model includes a designation of the logical element and an actual expression of the logical element, and a limit condition for an attribute of the character string is established to the actual expression. 7. The non-transitory computer-readable recording medium according to claim 5 , wherein, the estimating determines, for the several selected logical elements according to the priority, the degree of similarity between the designation of the logical element and/or the actual expression of the logical element associated respectively with a logical element at an upper level, a logical element at a lower level or a logical element at the same level in the hierarchical structure of the reference logical element and the extracted character strings, and estimates, based on the result of the determination, the degree of similarity between the logical structure stored in the logical structure model, and the logical structure among the extracted character strings in the input image.