DBObjectHandle :: StartReadTransaction - Start read transaction

Starting a read transaction will cache all system events generated for external registered application resources (registerProperty()). The last event for each event class is cached. Caching a higher class events will remove lower class events. The level of an event class is defined by its enumeration value (high order byte).

Read transactions can be nested. Each read transaction started should be terminated, since otherwise, no events are generated anymore for registered handles.

Cached events will be released, when the last read transaction is closed. When the object space handle is invalid, the function throws an exception.