HP NonStop G-Series - Manual (Page 44)

Tape File Concepts
DSM/Tape Catalog User’s Guide — 520233-008
2 - 4
Relative Generations
Example
This example shows four generations of CALIF_ACCOUNTS in a file catalog as of
January 27:
On January 27, a special report is needed from the data in the second generation of
CALIF_ACCOUNTS on tape X00025. This DEFINE is used to retrieve that generation:
6> ADD DEFINE =REPORT_IN, CLASS TAPECATALOG,&

6> & USE IN,&

6> & FILEID CALIF_ACCOUNTS,&

6> & GEN -3
On January 28, the catalog entry for the second generation of CALIF_ACCOUNTS is
deleted using the DELETE TAPEFILE command because the tape was destroyed. The
catalog entries and their generations numbers are now:
There is a numbering gap between absolute generation 1 and 3, but the relative
generation numbers have no gap. A tape file request by absolute generation number is
possible for generations 1, 3, and 4 only.
You can still request each entry by a relative generation number but asking for relative
generation -3 on January 28 now retrieves CALIF_ACCOUNTS on tape X00015.
Requesting generation -3 on the previous day would have retrieved
CALIF_ACCOUNTS on tape X00025.
Tape File Name Tape Name
Absolute

Generation
Relative

Generation Date Created
CALIF_ACCOUNTS X00015 1 -4 January 6
CALIF_ACCOUNTS X00025 2 -3 January 13
CALIF_ACCOUNTS X00032 3 -2 January 20
CALIF_ACCOUNTS X00045 4 -1 January 27
Tape File Name Tape Name
Absolute

Generation
Relative

Generation Date Created
CALIF_ACCOUNTS X00015 1 -3 January 6
CALIF_ACCOUNTS X00032 3 -2 January 20
CALIF_ACCOUNTS X00045 4 -1 January 27