DDSXTY12 — Improving Extensible Types

Extensible Types do not support monotonic extensions of nested struct types. Adding support for monotonic extensibility of nested structures is straight-forward and requires only a very small change to the existing specification.

Our suggestion is to allow for monotonic extensibility at any level in the type structure and accommodate this by serializing a length parameter before any nested structure.

No @Id should be serialized since it is likely that user won't specify IDs when using Extensible types and relying on Ids could break the whole scheme.

Note that this no longer needs to address DDSXTY12-15 as that issue is already addressed by the resolution DDSXTY12-145

Improving Extensible Types

In DDS-XTYPES 1.1 there are 3 extensibility kinds: Final, Extensible, Mutable. And two encoding formats: PLAIN_CDR and PL_CDR.

In DDS-XTYPES 1.2 we are adding 2 encoding formats: DELIMITED_CDR and ENHANCED_PL_CDR.

For simplicity and backwards compatibility DDS-XTYPES 1.2 keeps the same 3 extensibility kinds. But uses the name "APPENDABLE" instead of "EXTENSIBLE". "EXTENSIBLE can still be accepted in the IDL for compatibility. When serializing data the Encoding format is determined by “Extensibility Kind” and the encoding version: