My question is : can i do the backup of db2 v8 database and restore to db2 v7 in the unix environment ..if yes where i can find some documentation ...

thank ......

No .. you cannot .. you can do v7 to v8 and the process will migrate the catalog and all other structures to the latest version ,,
But going from a higher version to lower is not supported (and doubt, will ever be supported)

sosdb,
Because backup/restore to previous version is not supported, you will probably need to do something like this:
1. db2look - to get database objects (primary keys, foreign keys, etc) run "db2look /?" for more help.
2. export tables
3. import or load tables

Hope this helps,
Grofaty

Another option for "restoring" the structure / data from this newer Database to a previous release would be the DB2MOVE feature.

You can find it easily in the Command Reference how to use this tool.

Hope this helps.

Fernando