18. A computer program product having a non-transitory computer-readable medium including programmed instructions for processing text information, wherein the instructions, in response to execution, cause a computing system to perform operations, including: extracting text document data from first document data of a first file; identifying a modification relation between a first character string and a second character string included in the text document data; embedding an attribute in the text document data, the attribute representing the modification relation; identifying the second character string as a document-specifying character string that specifies second document data of a second file differing from the first file; embedding a document tag in the text document data, the document tag identifying the document-specifying character string; receiving an input character string; determining that the input character string matches the first character string in the text document; in response to the determining, identifying the document-specifying character string having the modification relation with the first character string based on the attribute and the document tag embedded in the text document data; and in response to the identifying the document-specifying character string, identifying the second document data represented by the document-specifying character string.
18. A computer program product having a non-transitory computer-readable medium including programmed instructions for processing text information, wherein the instructions, in response to execution, cause a computing system to perform operations, including: extracting text document data from first document data of a first file; identifying a modification relation between a first character string and a second character string included in the text document data; embedding an attribute in the text document data, the attribute representing the modification relation; identifying the second character string as a document-specifying character string that specifies second document data of a second file differing from the first file; embedding a document tag in the text document data, the document tag identifying the document-specifying character string; receiving an input character string; determining that the input character string matches the first character string in the text document; in response to the determining, identifying the document-specifying character string having the modification relation with the first character string based on the attribute and the document tag embedded in the text document data; and in response to the identifying the document-specifying character string, identifying the second document data represented by the document-specifying character string. 19. The computer program product according to claim 18 , the operations further including obtaining the second document data in response to the identifying the second document data.