DDS15 — Specify the allowed IDL Types within DDS Topic structs

The DDS Spec (as of v1.2) does not specify the set of IDL types that are allowed in a DDS Topic struct. This should be defined and made normative instead of being left as an implementation detail.

Discussion:

Because the set of IDL types allowed in a DDS Topic struct is not defined, implementors are at liberty to decide what set of IDL types to support. Concerns about the impact of the lack of standardization in this area have been raised by the computing infrastructure teams on major Navy programs on several occasions particularly in regards to potential impact on code portability across DDS implementations and interoperability between DDS implementations.

In reviewing the DDS C++ Native Language Mapping RFP, we commented that the RFP provided an opportunity to insert a requirement to define the allowed C++ types within a DDS Topic struct which would indirectly result in defining the set of allowed DDS IDL types due to the RFP requirement for the C++ mapping to be consistent with the IDL mapping. This suggestion was rejected because it was viewed that the correct forum and mechanism for resolving this issue was the DDS RTF. We were requested to submit this as an issue to the RTF since the RTF could probably resolve this issue within the next 6 months.