[aerogear-dev] Sync data model comparison

[Summers Pittman]

So I'm not sure I see how the data model in the current sync spec helps 
with syncing data.  Also the current spec draft is lacking a transport 
format as well.

I propose using the dual shadow data model described here: 
https://neil.fraser.name/writing/sync/

## Data Model: and Transport:

Client side each piece of data which is currently in active 
synchronization (ie the client is sending AND receiving updates at the 
same time) has a copy of her data which represents the current assumed 
good synchronized state.  She also has the copy of the data she is 
editing.  When she has finished her edit (for an use case specific 
defined by the developer definition of finish) the system will generate 
a diff based on the JSON representations of her shadow and her model.  
The model will replace the shadow and a diff of her data as well as a 
checksum of her data will be sent to the server for processing.

Server side the server will maintain its own model of the shared data, 
as well as shadows for each session currently sync the data. When it 
receives a sync, the diff will be applied to the server's shadow of the 
session which sent the diff.  If the diff merges cleanly and the 
checksum of the server shadow matches the checksum in the transport, 
then the server will update the canonical model of the data against what 
was in the session's updated shadow.  The server will then diff all of 
its sessions' shadows against its model and send out diff messages to 
the clients.

I've made a spreadsheet* where I follow one of QMX's sample applications 
and step through a few workflows with my proposed data model.  (This is 
the data model I use in the DevNexus sync demo and the real time text 
demo).  I would welcome someone to implement the use case with QMX's 
proposed data model.

* 
https://docs.google.com/spreadsheet/ccc?key=0AjSy-Z4v4qE-dGhESFU5R1BSWTF3RnliMjVic3JnbXc#gid=1

wdyt?  Who would mind doing the data flow for the other model?