1. An information retrieval system for retrieving information from a database, comprising:
a parser for parsing a natural language query into its constituent phrases to produce a syntax analysis result;
virtual table for converting phrases of the natural language query to retrieval keys possessed by the database, said virtual table accounting for particles that modify the phrases;
a collating unit for preparing a database retrieval formula from the syntax analysis result by selecting a virtual table that is used to convert the phrases of the natural language query to keys possessed by the database; and
a retrieval execution unit for retrieving data from the database on the basis of said database retrieval formula.

2. An information retrieval system as recited in Claim 1 further comprising;
an additional table for converting an undetermined value phrase in the natural language query into a determined value phrase in the database based on the syntax analysis result.

3. An information retrieval system as recited in Claim 1 further comprising;
a terminology dictionary for identifying entries in the virtual table to be used in converting the phrases of natural language query, said dictionary including words representing time, and said terminology dictionary being used by the parser in obtaining the syntax analysis result; and
a time interval definition table in the virtual table for defining dates corresponding to said words representing time.

4. An information retrieval system as recited in Claim 1 further comprising;
a database retrieval formula conversion unit for generating a formula in a database retrieval language from the database retrieval formula.

5. An information retrieval system for retrieving information from a database, comprising: :
a parser for parsing a natural language query into its constituent phrases to produce a syntax analysis result;
virtual table for converting phrases of the natural language query to retrieval keys possessed by the database, said virtual table accounting for particles that modify the phrases;
a collating unit for preparing a database retrieval formula from the syntax analysis result by selecting a virtual table that is used to convert the phrases of the natural language query to keys possessed by the database;
a retrieval execution unit for retrieving data from the database on the basis of said database retrieval formula;
an additional table for converting an undetermined value phrase in the natural language query into a determined value phrase in the database based on the syntax analysis result; ;
a terminology dictionary for identifying entries in the virtual table to be used in converting the phrases of natural language query, said dictionary including words representing time, and said terminology dictionary being used by the parser in obtaining the syntax analysis result;
a time interval definition table in the virtual table for defining dates corresponding to said words representing time; and
a database retrieval formula conversion unit for generating a formula in a database retrieval language from the database retrieval formula.