In many applications there are variables with values that are changing and variables with constant values.
Currently, there is no standard way to expose the information whether a value is constant and thus a client would need to subscribe to the constant variables as well.

It would be desiarable to provide this information on the attribute level so it can be applied to Properties (typically, rather Properties than DataVariables have constant values).

We could extend the AccessLevelEx attribute like done in Mantis Issue 0004422.

If we do, we need to clarify what Constant means

1. Forever (I would not assume this case in most cases)
2. Until Server restarts
3. Until configuration changes, that might occur while server is running

In case 2 it would be desirable and in case 3 required to have something like a global ConfigurationVersion that would be updated, when the configuration has changed.

Motivation of this issue is, that we actually need such a functionality in the "Relative Spatial Location" subgroup of the Harmonization WG. We could solve it there with Properties, but it would be desirable to have a more common solution, and it cannot be solved with Properties on Properties.