[Nfd-dev] Naming conventions for "sequence number"

[Alex Afanasyev]

Hi Jeff and all,

We had a follow up discussion today about naming conventions and in particular we got to one question about "sequence numbers".   The CCNx naming convention that we going to revert for now defines markers for segments (sequential and non-sequential) and marker for version.  What this convention is missing is the marker for sequential sequence numbers for "infinite" collection.  Examples of this could be stream of generated notifications n NFD, dataset in ChronoSync, frames in webrtc (?).  In the past, we kind of used "segment" convention to represent such numbers, but during our discussion we agreed that there is different semantics for "segments" and "sequence numbers" and it is useful to explicitly distinguish between them:

- "Segment" is a Data packet that is a part of a bigger data blob (e.g., segments of one frame).  If third party (repo, cache, library?) understands this semantics, than it can try request all the segments and stop when finished.

- "Sequence number" (for "infinite" collections) denotes that the particular Data object is part of the collection, but is independent piece of this collection (individual frame).   It is also possible that such a piece can be further segmented.   If third parties understand this semantics, they can perform very different actions compared to segments.   

The proposal at hand is that we not just define markers for "segment" (%00 prefix) and "version" (%FD) as it is in NFD, but also add a new notion of sequence numbers (say, %FE for now).

This definition doesn't imply we need to do any immediate change in any of the application we have.  It is just for the future applications/updates we use a more semantically correct ways to mark out sequence numbers.  This will also prepare libraries for any convention change later.  The place where we plan to use it right away is in NFD notification stream protocol (http://redmine.named-data.net/projects/nfd/wiki/Notification).

Can you give opinions about this proposal?

---
Alex