The lock mode controls how several users can access the same data records at the same time. The lock mode can be assigned separately for each Basis table. When the lock is set, the corresponding entry is stored in the system lock tables for each Basis table.

The following methods of synchronizing access by several users can be distinguished:

E (exclusive): This mode means that locked data may only be displayed or processed by a single user at any one time. A request for another exclusive lock or for a shared lock will be rejected.

S (shared): This mode means that several users can simultaneously display the same records. A request for another shared lock is accepted, even if it is requested by another user. A call for an exclusive lock is rejected.

X (exclusive but not cumulative): Locks of type E can be called several times from the same transaction and are removed successively. In contrast, a lock of type X can be called only once. Any other call for such a lock is rejected. A lock of type X is not accepted if another lock of type E is already set.