12. A method of providing related words for a query using a search system for providing related words composed of a client and a server connected to the client through a network, the method comprising: searching for a co-occurrence frequency by words from source data, wherein the co-occurrence frequency indicates how many times at least one second word occurs in relation to at least one first word; storing the result of the search in a database; receiving an input of a query from the client; searching for third words co-occurring by at least one of the second words; determining that the at least one of the second words is related to at least one of the first words if the third words include the at least one of the first words; and extracting related words related to the input query from the database, wherein the extracting the related words reads the co-occurrence words by specified words from the relational database, extracts N upper co-occurrence words by the specified words in the order of the co-occurrence frequency, extracts second co-occurrence words with respect to the N co-occurrence words when the co-occurrence words occur, and judges the co-occurrence words for the specified word as being related words if the specified word among the second co-occurrence words is within the order predetermined by the co-occurrence frequency order.
12. A method of providing related words for a query using a search system for providing related words composed of a client and a server connected to the client through a network, the method comprising: searching for a co-occurrence frequency by words from source data, wherein the co-occurrence frequency indicates how many times at least one second word occurs in relation to at least one first word; storing the result of the search in a database; receiving an input of a query from the client; searching for third words co-occurring by at least one of the second words; determining that the at least one of the second words is related to at least one of the first words if the third words include the at least one of the first words; and extracting related words related to the input query from the database, wherein the extracting the related words reads the co-occurrence words by specified words from the relational database, extracts N upper co-occurrence words by the specified words in the order of the co-occurrence frequency, extracts second co-occurrence words with respect to the N co-occurrence words when the co-occurrence words occur, and judges the co-occurrence words for the specified word as being related words if the specified word among the second co-occurrence words is within the order predetermined by the co-occurrence frequency order. 17. The method as claimed in claim 12 , wherein the searching for the co-occurrence frequency is executed for a predetermined period.