FLC's expectation isd:

• if a variable is selected as target variable, and if the SubscribedDataSet the target variable is assigned to is referenced by a enabled DataSetReader, the variable is set to read-only for any access, excluding the DataSetReader.
• If a variable is selected as target variable by multiple SubscribedDataSets, only one of them may be referenced by an enabled DataSetReader.

Writing the requirement to the spec is easy. But we need to come up with some generic functionality that can be implemented in base libraries to avoid that every implementer of a Write needs to have special logic.

Option for indicating "locked" state would be

• Use reserverd AccessLevel bit 7 for 'Locked'
• Introduce new attribute like AccessLevel for Methods or a general solution for all node classes

[Edit based on discussion on January 19, 2021]
It would be much easier to use the AccessRestrictions for a new 'Locked' flag. This attribute is available for all NodeClasses.
We can still reflect the locked state in the UserAccessLevel.
Discuss in next meeting
[Edit end]

Indication of who is locking is necessesary - reference to the locking object (DataSetReader, Lock) may be a good solution.

Discussion in UA WG Meeting:
There is an agreement that adding a IsLocked flag to the AccessRestrictions is the right way to indicate the locking state on a node.
For Methods the flag would influence the UserExecutable Attribute.
For Variables the flag would influence the UserAccessLevel Attribute.

Open Issue:
How is the information provided about the owner of a lock.

We need the locked state also for the PubSub configuration objects managed by a FX connection. These objects cannot be modified through the PubSub API

discussed in UA meeting - see new related issue for results.