1. Field of the Invention
The present invention relates to a database search method, and more particularly to a database search method capable of hiding search objects from anyone except for a client who issues a query.
2. Related Art
Recently, much genetic information such as DNA, has been figured out and its results are stored in a variety of databases such as a motif database. Consequently, as for the analysis results of DNA, one can search related information using these databases.
For example, a motif database is the one that collects various patterns relating to functions of DNA and protein, etc. This database stores patterns such as the following.                A..T..ATAT...CGATGA (“.” represents any character)        A..[AT]..ATCG.A (“[AT]” represents A or T)Therefore, collating DNA analysis results, one can find what patterns the analysis results contains, that is, what functions associated DNA holds.        
On the other hand, it is often the case in such database search that the query includes private information or confidential information about research and development, thus a leak of such information is worried about. Conventionally, in order to prevent a leak of information in database search, a method has been used for encrypting data relating to a query or a search technique called private information search.
As described above, when performing database search using published databases, information contained in a query might leak so that there exists a need for means to effectively prevent a leak of information.
As one of search methods that use encrypted data to prevent a leak of information, there is one that transmits a query including encrypted data to a database, where the encrypted data is decoded before search processing is performed and then the results are returned. In this regard, there exist various techniques for encryption.
However, since this method needs a function to decode encrypted data on the part of a database, it takes a lot of trouble with introduction.
Furthermore, as an owner of the database knows the contents of the query, there remains a likelihood that information leaks.
On the other hand, private information search is a method where a query is issued without informing an entry of a database that is desired to be known. Accordingly, this method theoretically assures the security in terms of information theory and prevents a leak of information completely.
However, this method involves particular operations on the database during a procedure, thus the database needs to be constructed in accordance with this search method. Therefore, a lot of trouble is again required with introduction.
In addition, since it is essential for the security that all of the entries of the database are referenced once, this method is impractical for large scale databases because a great amount of search time is required.
Besides there is inconvenience in that ambiguous search is not allowed that is essential for dealing with data sequence matching.