Definitions - Multi-User Considerations (Magic xpa 3.x)

The following are terms necessary for the understanding of the multi-user issues explained in this section.

Isolation Level – Determines what happens during the concurrent (simultaneous) use of the same transaction. The user can change the Isolation level in the database only. Changes made in the DBMS Properties dialog box have an effect on the system.

Locks – Locks are used to preserve data integrity. When a user updates data, some notification should appear, so other users do not update the same data. Other users of the same data must receive a notification that the data is currently being updated. This notification is called a lock.

When no lock is issued, updated information can be lost. If each user transaction is unaware of the other, the last update overwrites the other updates.

Process – A process is an instance of a program running in a computer. It is close in meaning to a task, a term used in some operating systems. Like a task, a process is a running program with which a particular set of data is associated so that the process can be kept track of. A project that is being shared by multiple users will generally have one process at some stage of execution for each user.

Transactions – A transaction is a sequence of Data Manipulation steps in the database that must be completed in its entirety before the database is actually updated. If something fails before the sequence is completed successfully, all changes will be undone (this is known as rollback). In other words, either the whole sequence is updated or none of it. This also preserves data integrity.