DDSXTY13 — Union discriminator value without associated member

The DDS-XTypes 1.2-beta1 document section 7.2.2.4.4.2 (Union Types) on page 34 first paragraph states:

> [...]
> (Note that it is not required for every potential discriminator value to be
> associated with a member.)

Supporting this, 7.4.3.5.1 (Notation used for the match criteria) on p.121 states:

> O : UNION_TYPE An object "O" of a Union type as defined in 7.2.2.4.4.2
> [...]
> * O.selected_member is the member of the union selected
> based on the value of the discriminator. Note that certain
> discriminator values may select no member.

However, 7.4.1.2.3 (Omission and Reordering of Members of Aggregated Types) on page 110 third para states:

> Because union members are identified based on a discriminator value,
> the value of the discriminator member must be serialized before the
> value of the current non-discriminator member.
> Neither member value may be omitted.

I suggest replacing "Neither member value may be omitted" by:

" The discriminator value may not be omitted.
If the discriminator value has an associated member then the member value may not be omitted. "

Section 7.5.2.11.6 (Operation: get_item_count) on page 185 states:

> The "item count" of the data depends on the type of the object.
> * If the object is of a union type, return the number of members in the
> object. This value will always be two: the discriminator and the current
> member corresponding to it.

I suggest replacing the last sentence by:

" This value will be two if the discriminator value has a corresponding member. It will be one if the discriminator value has no corresponding member. "

Modify the 7.4.1.2.3 description of union serializarion

Indicate that in the case of a union the only mandatory thing to serialize is the discriminator. The member may be omitted if no branch is selected.