Method and system for expanding document retrieval information

In a computer system for retrieving a document containing a search character string specified by an operator in a search through text documents that are produced by performing character recognition processing on image documents, a search character string expanding method comprising:

• a search character string dividing step of dividing the entered search character string into partial character strings each consisting of a predetermined number n of characters (n≧2);
• a similarity table referencing step of checking the n-character partial character strings (n≧2) against an n-character-based similarity table, the n-character-based similarity table being generated in advance by storing character strings of similar character shapes that are highly likely to be erroneously recognized, each consisting of a plurality of characters and arranged in an order of magnitude of emergence probabilities in each group;
• and
• a search character string expanding step of extracting groups of similar character strings by checking the partial character strings making up the search character string against the n-character-based similarity table and combining the extracted similar character strings to generate expanded words, each having a product of the emergence probabilities of the similar partial character strings.

A program read into and running on a computer to expand a character string, wherein the character string is entered to search image information of documents, the program comprising:

• a character string dividing step of dividing the entered character string into a plurality of partial character strings each having a plurality of characters;
• a similarity table previously storing groups of similar partial character strings each consisting of a plurality of characters and arranged in an order of magnitude of emergence probabilities in each group, each of the groups of the similar partial character strings being derived from each of the plurality of partial character strings obtained from the character string dividing device by changing at least one of the characters of each partial character string to a different character which is similar in shape;
• a referencing step of referencing the similarity table previously storing groups of similar partial character strings, each consisting of a plurality of characters and arranged in an order of magnitude of emergence probabilities in each group, each of the groups of the similar partial character strings being derived from each of the plurality of partial character strings obtained from the character string dividing step by changing at least one of the characters of each partial character string to a different character which is similar in shape;
• and
• an expansion step of combining the plurality of similar partial character strings given by the referencing step into expanded words, each having a product of the emergence probabilities of the similar partial character strings, and store them in an expanded word table.