Document retrieval system using analog signal comparisons for retrieval conditions including relevant keywords

A document retrieval system for retrieving a registered document from a document database responsive to a designated retrieval condition including one or a plurality of designated keywords, said document retrieval system comprising:

• a) storage means for storing:
• 1) keyword relationships which indicate relationship values of keywords;
• and
• 2) relations of the keywords and registered documents;
• the storage means having a storage means output portion;
• b) input means for designating a retrieval condition including one or a plurality of designated keywords, said retrieval condition determining a registered document which is to be retrieved from said storage means based upon an analog signal comparison, the input means having an input means output portion;
• c) selection means, coupled to said storage means via the storage means output portion and coupled to said input means via the input means output portion, for:
• 1) selecting a plurality of keyword relationships based on the retrieval condition;
• and
• 2) converting the selected keyword relationships into analog signals;
• the selection means having a selection means output portion;
• d) analog operation means, coupled to said selection means via the selection means output portion, for calculating a relevance of document based on the analog signals received from said selection means, the analog operation means having an operation means output portion;
• and
• e) conversion means, coupled to said analog operation means via the operation means output portion, for converting into a digital value the calculated relevance of document received from said analog operation means via the operation means output portion, the conversion means having a conversion means output portion.