HP Integrity NonStop J-Series - Manual (Page 90)

CREATING AND RUNNING A MULTIFILE APPLICATION
Do the Files Contain Related Information?
Notice that the "empnum" field of the "employee" record
description matches the "emp-no" field of the "dependents" record
description. In this case both fields have the same data type:
PIC 9 or numeric. If you are not sure that two fields have
compatible data types, refer to the ENABLE Reference Manual for
more information.
When fields from two files match, you can use them as join fields
to establish a logical connection between the two files. When
you generate a multifile application, each file must have at
least one join field that can be used to link it to another file.
If an application accesses more than two data base files, some
files may have more than one join field forming links to other
files.
ENABLE has one other requirement for multifile applications:
when you link two files, the join field of one of the files must
be a key field. In Figure 5-3, both of the prospective join
fields ("empnum" and "emp-no") are key fields. "Empnum" is a
primary key field and "emp-no" is the leading portion of a group
field ("dep-key") that is also a primary key field.
If your files do not have appropriate join fields, you cannot use
ENABLE to generate an application to maintain them.
Do the Files Contain Related Information?
When you generate a multifile application, the files being
accessed should contain related information.
An ENABLE application uses the join-field value of one file to
locate or insert a record in another file. If the join fields
do not contain related information, the application might not
perform in the manner you expect, even though the values in the
join fields are compatible.
Suppose, for example, that you try to generate an application to
access a file that contains employee information and a file that
contains parts information. Suppose further that the join fields
of these files are: "enpnum" (containing a four-digit employee
number) and "partnum" (containing a four-digit part number).
Although ENABLE could generate this application, you could not
use it in any meaningful manner because no logical relationship
exists between employee numbers and part numbers.
When your data base files do not contain related information,
consider using several single-file applications to access the
files.
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