[cap-talk] request for comments on capability design

[Peter Amstutz]

On Thu, May 17, 2007 at 09:29:56AM -0400, Sandro Magi wrote:

> The web-calculus is not necessarily tied to the http model. It 
> implements a distributed object semantics that currently has a binding 
> to http. Your use case seems to require low-latency, and potentially 
> high bandwidth, so it would be interesting to see whether the 
> web-calculus can scale. The Java server with the relevant web-calculus docs:
> 
> http://waterken.sourceforge.net/

I see, the term 'web' is used in a more generic sense of an 
interconnected graph, rather than the WWW specifically.

Yes, you are exactly right.  The use case for online 3D graphics 
requires juggling both short, low-latency, short lived data (position 
updates) with large, high-bandwidth, long-lived data (art assets like 3D 
models and textures).  To make things more difficult, for the kind of 
streaming platform I am working on, these two types of data need to be 
transmitted simultaneously.

Because prioritizing data transmission this way reaches down to the 
lowest level of packet scheduling (effectively it requires implementing 
application-level QoS), it requires awareness by the rest of the system 
all the way up to the application layer.  I have yet to encounter a 
distributed system that properly addresses these requirements [1], which 
is fundamentally why I'm compelled to write my own.  Thus, it is as much 
basic technical implementation issues, and not overall architechture, 
that is the basis for decision.  Also, if the underlying ideas are good, 
why shouldn't they be generic and implemented over and over again :-) 
Capabilities as a design pattern?

[1] Let me qualify that with "and is also free software", since the goal 
here is to build a free software platform for 3D virtual worlds, so it 
has to be free if I am going to reuse it.

> See also the sidebar of:
> 
> http://wiki.erights.org/wiki/Walnut/Secure_Distributed_Computing/E_Capabilities
> 
> It briefly discusses the Croquet project (essentially what you're doing) 
> and how capabilities can be used in such an application.

I am familiar with Croquet, and certainly interested in borrowing some 
of their better ideas.  However, I'm not sure if they've really tried to 
tackle the question of security beyond collecting requirements as 
documented on the page you linked to.  Their distributed computing model 
also seems to make the notion of "ownership" very ambigious, so I'm not 
sure how you would go about specifying that only a subset of 
participants in a Croquet space can modify some shared object.

-- 
[   Peter Amstutz  ][ tetron at interreality.org ][ peter.amstutz at gdit.com ]
[Lead Programmer][Interreality Project][Virtual Reality for the Internet]
[ VOS: Next Generation Internet Communication][ http://interreality.org ]
[ http://interreality.org/~tetron ][ pgpkey:  pgpkeys.mit.edu  18C21DF7 ]

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