A single SAS
observation can be composed of one or more SYSTEM 2000
database records. Therefore, a single UPDATE
command in SYSTEM 2000 to update a given observation might involve several internal SYSTEM
2000 UPDATE commands. If one of these UPDATE commands fails after several others have
executed, the status of the entire update is incomplete.
In order to guarantee the data integrity, you must enable the
rollback feature. You can do this easily with the
QUEST procedure, by issuing the ENABLE ROLLBACK statement in the
CONTROL language. When you enable rollback, you must make sure that the Rollback Log (database
File 8) and the
Update Log (database File 7) are allocated. With rollback enabled, SYSTEM 2000 can roll back
the database to its status before the sequence of commands that triggered the error.
If rollback is not enabled, partial updates can occur if error return codes are received.
Errors
can occur from security violations or from bad data. For example, data that does not
match the
SAS informat, or data that has too many significant decimal places for a specific item's numerical
precision. Also, if LHOLD=YES is specified in the SYSTEM 2000 execution parameters
and rollback is not enabled, the
interface view engine can receive
return code 111, which causes an update to be rejected.