DSM/Tape Catalog User's Guide

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 t

ape 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_ACCOUNT

S 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