columnName is the name of the column or property whose values reference objects in an extent. That means that this expression can be used to return an object reference: set objectRef = $classmethod(,"%OpenId",rs.%Get())

exportCall is the tag^routine() expression that implements the object export for a given object ID. The following code will export an instance of extentName: set %rowid = rs.%Get(), %nolock = 0 do @

extentName is the name of the extent in which the value of columnNbr is an instance. This is a class name but the object referenced can be an instance of a more specific subclass of extentName.