Dictionary/3000 Reference Manual (32244-90001)

Appendix D 335
How HP INFORM Links Files to Generate Reports
Default File Access
Default File Access
HP Inform/3000 provides defaults designed to maximize performance of the file accesses
necessary during report production. One such default, which was explained in the
discussion on the driving file, is that an MPE file will be used as the driving file whenever
possible. In addition, if file names (in response to the FILE prompt) and link values that
override the defaults have not been specified, HP Inform/3000 will try to follow these
guidelines:
• Involve as few files as possible in the access.
• Access a KSAM file in preference to a database (since there is less overhead involved).
• Open as few databases as possible.
• Use master data sets whenever possible (since they will need to be accessed only once
per key value, while detail data sets and KSAM files may require several accesses per
key value).
Note that by specifying a file name in response to the FILE prompt, HP Inform/3000's
access algorithm may not work efficiently and possibly not at all. It is best to not specify a
file name in response to the FILE prompt unless necessary to ensure that the correct
values of an element are retrieved. If a file name is specified when it is not necessary to do
so, it is possible that more files will be accessed than HP Inform/3000 would otherwise
access. In the worst case, it may result in HP Inform/3000 being unable to create a link -
when there is no link element to the designated file.
HP Inform/3000 uses link elements to accomplish the above goals; the link elements are
used in the order which produces maximum performance. The use of link values assigned
to elements allows you to override this - to control which elements are tried to link files
and in what order. However, the ability of HP Inform/3000 to maximize performance may
be hampered by the improper use of link values.