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Naive method to map stored format to presentation format

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• The naive way to present the stored information to users

  • Naive way to present the stored information to users:

    Present the stored information in the same format as the information is stored

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  • Consequence:

    In order to satify the need of each group of users: We store their required data format in a (separate) data file.

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  • Example: suppose we have 3 different applications on students

    Grade report Financial record           Health report

  • We maintain one data file per application:

    Grade Report Financial record (other files) StuID Name Course Grd StuID Name Due +-----+----------+-------+----+ +-----+----------+------+ ..... | 123 | John Doe | CS171 | A | | 007 | James Bo | 2000 | +-----+----------+-------+----+ +-----+----------+------+ | 123 | John Doe | CS255 | B | | 123 | John Doe | 1500 | +-----+----------+-------+----+ +-----+----------+------+ | 007 | James Bo | CS170 | A | +-----+----------+-------+----+ | 007 | James Bo | CS171 | B | +-----+----------+-------+----+

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• Problem with the naive approach
  • Problems with this naive approach:

    Some information may be stored multiple times (wastage of storage space) Example: The fact that 123 is the student ID of "John Doe" is stored 3 times Grade Report Financial record (other files) StuID Name Course Grd StuID Name Due +-----+----------+-------+----+ +-----+----------+------+ ..... | 123 | John Doe | CS171 | A | | 007 | James Bo | 2000 | +-----+----------+-------+----+ +-----+----------+------+ | 123 | John Doe | CS255 | B | | 123 | John Doe | 1500 | +-----+----------+-------+----+ +-----+----------+------+ | 007 | James Bo | CS170 | A | +-----+----------+-------+----+ | 007 | James Bo | CS171 | B | +-----+----------+-------+----+ Duplicate information storage can cause data inconsistency if updates are not applied consistently Example: before Grade Report Financial record StuID Name Course Grd StuID Name Due +-----+----------+-------+----+ +-----+----------+------+ ..... | 123 | John Doe | CS171 | A | | 007 | James Bo | 2000 | +-----+----------+-------+----+ +-----+----------+------+ | 123 | John Doe | CS255 | B | | 123 | John Doe | 1500 | +-----+----------+-------+----+ +-----+----------+------+ | 007 | James Bo | CS170 | A | +-----+----------+-------+----+ | 007 | James Bo | CS171 | B | +-----+----------+-------+----+ James Bo asks the Financial Record keeper to change his name to James Bi Grade Report Financial record StuID Name Course Grd StuID Name Due +-----+----------+-------+----+ +-----+----------+------+ ..... | 123 | John Doe | CS171 | A | | 007 | James Bi | 2000 | +-----+----------+-------+----+ +-----+----------+------+ | 123 | John Doe | CS255 | B | | 123 | John Doe | 1500 | +-----+----------+-------+----+ +-----+----------+------+ | 007 | James Bo | CS170 | A | +-----+----------+-------+----+ | 007 | James Bo | CS171 | B | +-----+----------+-------+----+ Result: we have inconsistent data !!!