HP Integrity NonStop J-Series - Manual (Page 158)

USING AN ENABLE APPLICATION
Courtesy Key
Alternate Key
An application can identify a single record or a set of records
by the contents of an alternate key field. If, for example, the
department number of an employee record is an alternate key, you
can retrieve all records of that file sequentially, in
department-number order.
Courtesy Key
ENABLE supplies a special courtesy key field for certain types of
files. An application can identify a particular record in one of
these files by the value of this courtesy key. The courtesy key
corresponds to a unique record number associated with each record
within a relative, entry-sequenced, or unstructured file.
For a relative file, the record number corresponds to the
physical position of the record within the file. The first
record position is 0, the next record position is 1, and so
forth. A record position exists whether or not a record has
actually been stored in that position.
For an entry-sequenced file, the record number corresponds to the
order in which a record is stored in the file. The first record
stored has record number 0, the next record stored has record
number 1, and so forth. The record numbers are always in
ascending order, but the numbering sequence is not always in
increments of one. Record 4096, for example, could follow record
32. The last record stored in the file always has the highest
record number.
For an unstructured file, the first record is record 0, the next
record 1, and so forth. The last record stored in the file
always has the highest record number.
When you insert a record with a courtesy key, you do not have to
supply a value for that key. Instead, the application can
provide a value for you.
As described later under "Labels and Fields," you can visually
identify a courtesy key field; however, you cannot visually
determine the type of file to which a courtesy key belongs. If
you need to determine the file type, ask your data administrator.
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