DDSIRTP23 — Key attributes and Regular attributes of a topic should be individually de-serializable

Key attributes and Regular attributes of a topic should be individually de-serializable (or at least make the keyhash compulsory)

[Nature] Architectural
[Severity] Major

[Description]
The "DDS Interoperability Wire Protocol v2.1" defines a a serialization format for topic types in which
it is not easy, nor efficient, to simply get access to the key of a given topic. This has to do with how CDR
serializes structs but could be worked around with the new X-Types specification.
In essence the problem is that some applications such as DDS routers (such as the PrismTech BlendBox)
require to perform some operations that while requiring a knowledge of the instance do not require the deserialization
of the data payload.

[Resolution]
For DDS implementation compatible with the X-Types ensure that the regular data attributes and the key attributes are serialized
in different chunks and thus individually accessible in an efficient manner – meaning to access the key I would prefer not to scan all
the regular attributes.

For non X-Types compatible DDS implementations make the KeyHash compulsory, meaning require DDS compliant implementation to
always send a key-hash along with a Data submessage.

No immediate need to add individual serialization of keys and regular attributes

The RTF does not see an immediate need to add the proposed functionality to the specification.