Devices commonly use bit-fields where each bit typically represents the status of some I/O, Alarm or the like.
In UA we have not specified a standard way to handle bit-fields. Therefore, some servers will use separate items, some will use arrays of bool, some servers will use complex types, some will just use an integer. Interoperability will be difficult to achieve.

I propose to explicitly support Bit-Fields up to 32 Bits. The value should look as follows:

  typedef struct
  {
       Value       UInt32;
       Valid       UInt32;
  } BitField;

"Value" would contain the Bit-Field. The "Valid" field specifies which bits are used.
On a Read (DataChange) "Valid" specifies all bits that have meaning.
On a Write the client specifies which bits it wants to be modified.

I propose to use a 32 Bit Integer so that the structure fits inside the Variant value (total of 64 bit).

In addition to this new DataType I propose a new Property "BitFieldDescription" with 32 entries of

  typedef struct
  {
       Name         String;
       Description  String;
  } BitDescription;

For missing (invalid) Bits the corresponding structure contains NULL Strings.
Alternatively we could add a BitNumber (0..31) to the structure. That way the array could only contain entries for valid Bits.

The property should be specified in Part 5 since Bit-Fields could be used in various information specs (DA and A&C in particular).