| 摘要 |
PURPOSE:To suppress the number of times of a trial of a data base retrieval to the number of times being below the number of elements, by holding a previous trial result as history information in the process for inquiring into the cause, in which the retrieval result is a null set. CONSTITUTION:This system consists of an inputted retrieval condition 1, a subset generating part 2 for extracting a subset of the retrieval condition from the retrieval condition 1 and using it as one combined candidate, a subset deciding part 3 for deciding the combined candidate of the retrieval condition generated by the generating part 2, history information 4 for holding a combination before it is used as a criterion by the deciding part 3, a command generating part 5 for generating an access command to a data base 7 from a combination of the retrieval condition which has succeeded in the decision of the deciding part 3, a command executing part 6 for executing the retrieval of the data base 7 by a command from the generating part 5, a history registering part 8 for registering the combination of the retrieval condition of that time to the history information 4, in case the data base retrieval result in the executing part 6 is not the null set, and a response generating part 9 for presenting the combination of its retrieval condition, when the retrieval result is the null set.
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