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1.                 From The Free On-line Dictionary of Computing (19 January 2023):
                   
   
   
                   
                     
   periodic group
      <database> (PE) Groups of logically related fields which occur
      multiple times within a group.
      Periodic groups are a non-relational technique.  An example
      of a PE would be for storing the history of a person's name
      changes, where name was kept in logically related fields such
      as surname, first name and middle name - with the person
      having changed their name more than once.
      [Clarification?]
      (1995-10-30)