When the interface is activated to perform an import or export, the Revit GUID value and the mapped tag number/code value are both included with the other parameter values. The interface service searches the WebTMA database first for an item in the Building with a matching GUID, then for an item with a matching tag number and an empty GUID value.
When exporting data from Revit to WebTMA, the error "Tag number already linked to other Revit UID" is returned if an item with a matching tag number exists with a different GUID. If no match is found for either the GUID or tag number, a new record is created. The Revit GUID value is set on the WebTMA record when that record is first created or updated by the interface.