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Directional Key Support for Closed End Boundary Checking

IP.com Disclosure Number: IPCOM000113195D
Original Publication Date: 1994-Jul-01
Included in the Prior Art Database: 2005-Mar-27
Document File: 4 page(s) / 107K

Publishing Venue

IBM

Related People

O'Brien, TR: AUTHOR [+3]

Abstract

A method for adjusting bounds for index probes is described. Adjusting the bounds can account for the four different inclusive/exclusive endpoint conditions. Included is the needed processing for search arguments being of different length than the index key definition.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 52% of the total text.

Directional Key Support for Closed End Boundary Checking

      A method for adjusting bounds for index probes is described.
Adjusting the bounds can account for the four different
inclusive/exclusive endpoint conditions.  Included is the needed
processing for search arguments being of different length than the
index key definition.

Glossary

o   Bounded key range

          A pair of key values which define the low and high bound of
    keys which will satisfy the desired equation.  This is used in
    the form of (Low bound) less than or equal to (retrieved key)
    less than or equal to (high bound).  If both ends of the bounded
    key range are the same value, it provides the mechanism to state
    that only one key value will satisfy the equation.

o   Key 'one less' or 'one more' than requested

          The key returned is different from the value given the key
    builder as input; however, there are no keys between the returned
    key and the input.

o   String comparison rules

          Shorter fields are padded out with blanks to the length of
    the longer field for the comparison.  For this discussion, assume
    the EBCDIC character set with x'40' for blanks.

    Trailing blanks are insignificant.

Changing the four different end point combinations into one - If the
operating system has been built in a structured manner, there is
likely a module or function that builds keys to be used in an index.
This module is enhanced such that instead of blindly taking the input
and producing a key, it can return a key either less than, equal to,
or more than the input.

The different functions added to a simple key builder:

1.  Return a minimum key

2.  Return a key 'one less' than the input

3.  Return a key equal to the input (standard existing function)

4.  Return a key 'one more' than the input

5.  Return a maximum key

      For the low bound of the range, as mentioned above, it needs to
be remembered if the extracted key should be strictly greater than,
or should it be greater than or equal to the input value.  This
information is known by the module building the bounded key range.
The bounded key range builder can take steps to hide this information
from any user of the bounded key range.  In the strictly greater than
case, this module can ask for a 'greater than' key.  This can be done
for the high bound also.  Now any bounded key range can be used as if
both ends are inclusive.

Varying length data and 'One more'

      Overview - The key builder also needs to be enhanced to know
the length of the value being passed in.

      The key builder can return the correct 'one more' key, since it
knows the definition of the key.  For example, if the value for the
key probe is 'ABC', a 'one more' key would seem to be 'ABD'.
However, this is not the case if the key definitio...