System-Defined Classes

When RODM is cold started, RODM initialization occurs and the class definitions are created. This data model provides the starting point for all RODM classes and objects. These system-defined classes enable users to access information about their application and about RODM itself. Figure 1 shows the RODM system-defined classes and their hierarchy.

Figure 1. RODM System-Defined Classes
This figure shows an example of RODM system-defined classes and their hierarchy.
RODM has the following system-defined classes:
UniversalClass
The root of the inheritance tree structure of the RODM data cache
EKG_SystemDataParent
The system data parent class, the parent of all RODM predefined system classes
EKG_System
The system object class, all the RODM system data created by RODM when you start RODM
EKG_User
The user object class, the fields and methods that RODM creates when an application connects to RODM
EKG_NotificationQueue
The notification queue object class, the fields and methods that RODM creates when an application creates a notification queue
EKG_Method
The method object class, the fields and methods that RODM creates when you install a method
The following six sections describe the six RODM system-defined classes. Information, which is common to all six classes, includes the following:
  • The fields that are created by RODM and can be accessed by application programs and methods.
  • The subfields that are created by RODM on system-defined fields. User applications cannot add subfields to fields of system-defined classes. You can add notification subscriptions to the specified fields using the EKG_AddNotifySubscription function.
  • The specification of the notify subfield identifies the fields to which an application can subscribe for notification. RODM notifies each application which has subscribed to a field when the value of the field changes.
  • Applications can change write-access fields only.
  • Applications can change values in the fields of objects only.