OPC XML-DA identifies properties by a string (a XML qualified name), instead of the numerical code used in OPC COM. For this a reason, a DAPropertyDescriptor and a DAPropertyElement have an additional QualifiedName property. When the component returns the DAPropertyElement from browsing, it fill is the information it knows about. When you pass the DAPropertyDescriptor to the component, you can fill in either PropertyId, or QualifiedName, or both. The component will use whatever is available and at the same time usable by the underlying technology. For the most common case, standard (well-known) properties can always be identified using their numerical ID, and the component will look up their qualified name automatically.

The DAPropertyElement (returned when you browse for OPC properties) contains an additional ItemPath property for OPC XML. For properties coming from OPC XML servers, if the property can be accessed as an item as well, the property is filled in with the string that together with the ItemId identifies the OPC item that corresponds to the OPC property.