To specify that a UA variable is readable (CurrentRead) in the TD, the term op must be assigned the value readproperty (as array entry). If the UA Variable is read only (you cannot write), the corresponding readOnly term of the DataSchema class in the TD should be set to true.

Since a readable UA Variable can be also subscribed by a Client, the term op must be supplemented by the value observeproperty and the observable term of the PropertyAffordance class in the TD should be set to true.

To specify that a UA variable is writable (CurrentWrite) in the TD, the op term must be assigned the value writeproperty (or has it as array entry). If the UA Variable is write only (you cannot read), the corresponding writeOnly term of the DataSchema class in the TD should be set to true.