[standards-jig] JEP--0084: Why avatars use PubSub

Thomas Muldowney temas at box5.net
Mon Jul 21 16:29:04 UTC 2003

On Sat, 2003-07-19 at 17:59, Bob Wyman wrote:
> In reading the Avatar JEP, I'm somewhat puzzled by the explanation
> provided for why PubSub has been used. The explanation provided is:
>     "Publish-Subscribe was chosen as the base layer 
>     for avatars because of the need to publish a large 
>     amount of data to any number of users. PubSub provides 
>     an easy mechanism for any user to subscribe to the 
>     avatar source and receive notifications from the publisher. 
>     Furthermore, the publiser only has to send the data once 
>     to the pubsub component, and it relays it to all the 
>     subscribers."
> Please forgive me if I'm being too picky about the wording here,
> however, the stress seems to be on PubSub being used because of the
> "large amount of data." I've always thought of PubSub as a tool for
> synchronizing state between systems. The amount of the state being
> synchonized doesn't seem relevant to whether or not PubSub is used. In
> this case, I suspect that the real problem isn't that there is a "large
> amount of data" that needs to be published to any single user but rather
> that the problem is that data needs to be published to a potentially
> large number of users. If this is the case, I would propose that you use
> words something like:
>   "Publish-Subscribe was chosen as the transport for
>    avatars since it is uniquely well suited to the task of 
>    publishing data to a potentially large, dynamic set of 
>    users. PubSub provides an easy to use mechanism allowing 
>    users to initially retrieve the avatar and 
>    subsequently receive avatar updates as soon as they are
>    published. PubSub simplifies the process of publishing
>    avatar updates by managing the distribution and updating of
>    the avatar on behalf of the publisher. The publisher only 
>    sends a single update of the avatar to the pubsub component
>    and that component then manages the distribution of the
>    updated avatar to all subscribing users."
> 		bob wyman

The reason you haven't seen me pushing this through is because I don't
like it either.  I think avatar data needs to be in an addressable data
store, and pubsub is used to only update the state and location of the
current avatar.  So like you say, pubsub would be used to synchronize. 
I'm planning to get further along on the JEP this week.


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