Natural language database retrieval system using virtual tables to convert parsed input phrases into retrieval keys

A computer implemented 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;
• a plurality of virtual tables for converting phrases of the natural language query to retrieval keys possessed by the database, said virtual tables accounting for particles that modify the phrases;
• a collating unit for preparing a database retrieval formula from the syntax analysis result by selecting at least one of said virtual tables 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 based on said database retrieval formula;
• wherein one of said virtual tables is a 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;
• wherein one of said virtual tables is a time interval definition 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.