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

[Alex Afanasyev]

Hi Lan,

Sequence number is not exactly a version.  A Data packet with the larger version should represent the same data, but just newer copy (say, two versions of nytimes webpage).  Sequence number is for completely different purposes, to represent independent Data items within a single data set/stream. Segments are for one data split into multiple chunks, e.g., for delivery purposes.

My take on markers is that their primary purpose is not describe the specific value, rather than define semantics of the value (which also implies specific syntax for the value).  If we name the version just "timestamp", then it wouldn't really mean anything for anybody outside the application. One would only know that this name component hold timestamp, but will be able only to guess the intention of the application to use timestamp in this component.

---
Alex

On Jul 16, 2014, at 5:10 AM, Lan Wang (lanwang) <lanwang at memphis.edu> wrote:

> Alex,
> 
> What is the difference between Version and Sequence number?  Is Version based on timestamps?  If so, it seems that Version should be explicitly called Timestamp.  
> 
> Lan
> On Jul 15, 2014, at 11:46 PM, Alex Afanasyev <alexander.afanasyev at ucla.edu> wrote:
> 
>> 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
>> 
>> 
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