Variable Storage, Retention, Access

This topic does not refer to the VTScada Historian or reporting features.

Within a VTScada application, you may need to share values between module instances. You may require values to remain in memory while an application re-starts, or you may want to control how values are shared across the servers running an application. You may also want to restrict access to variables between modules. These tasks are achieved by the use of the following keywords, assigned when defining variables.

Network Values - Variables used to update changes on all workstations and servers in a multi-server application.
Persistent Variables - Shared variables whose values are kept in a file in addition to RAM so that they can be reset after a server restart.
Protected Variables - Variables that cannot be used by modules outside the immediate scope.
Retained Variables - A variable that is persisted but not shared.
Shared Variables - Values that are shared between modules, but which are not saved to disk.
Temporary Variables - Short-lived variables that will disappear when VTScada is shutdown and restarted.