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Information retrieval system and method

  • US 5,732,260 A
  • Filed: 08/31/1995
  • Issued: 03/24/1998
  • Est. Priority Date: 09/01/1994
  • Status: Expired due to Fees
First Claim
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1. An information retrieval method for extracting topicality by a computer process from a database consisting of a plurality of data elements, each data element having time information and containing information that can be treated as keywords, said method comprising the steps of:

  • (a) determining the consistent frequency of appearance for a given keyword, said frequency being defined as an estimated number of data elements having time information within a unit of time, which data elements consistently contain said given keyword contained in said data elements over a predetermined period of said time information;

    (b) along the axis of said time information, determining the time at which the value obtained by subtracting said consistent frequency of appearance from the number of data elements having time information for each unit of time, which data elements contain said given keyword, becomes maximum, as the beginning of the topicality of said given keyword;

    (c) along the axis of said time information, determining the time later than the beginning of said topicality and at which the number of data elements having time information within a unit of time, which data elements contain said given keyword, becomes substantially as low as said consistent frequency of appearance, as the end of said topicality of said given keyword;

    (d) previously providing a model as a function of change in the frequency of a topic, said function monotonically decreasing from the beginning to the end of a topic, said function characterized in that the absolute value of its negative gradient gradually decreases along said time axis;

    (e) determining the distance between said function previously provided as a model and the graph of the change in a value obtained by subtracting said consistent frequency of appearance from the number of data elements having time information for each unit of time from said beginning to said end of said topicality; and

    (f) in response to the value of said distance for said given keyword being smaller than a threshold value, selecting said given keyword as a topic.

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