[MUD-Dev] Re: PDMud (was Re: Bruce Sterling on Virtual Community goals)

J C Lawrence claw at kanga.nu
Thu Oct 22 20:41:22 New Zealand Daylight Time 1998

On Thu, 22 Oct 1998 20:46:17 -0600 
Chris Gray<cg at ami-cg.GraySage.Edmonton.AB.CA> wrote:

> [Niklas Elmqvist:]

> Hmm. This is starting to sound a lot like an inverse polling. Send
> something out, everyone looks at it to see if they can handle it,
> and some do, some don't. Then something has to try to put any output
> back together again. Starting to sound inefficient, to me. Need more
> details!

I believe the model name you are looking for is "publisher/subscriber"
a technique that TIBCO (a company I keep interviewing at but have yet
to work at) believes they invented.  The following from
http://www.rv.tibco.com/faq.html#431761 summarises well enough with
only a moderate sale pitch



The publish/subscribe model supports distributed computing where one
application can send the same message once and multiple applications
receive it. Contrast the client/server model, where a client makes a
request of a server and the server returns results to fulfill the


In the event-driven model, the producer of information makes it
available by sending it over the network. The consumers of information
get information by using event callback functions that are triggered
when a certain condition is met. The producer of information has the
responsibility to initiate the sending of information.

An event-driven application supports asynchronous communication where
communication is unilateral and typically "one-to-many". The source of
the information may be of no interest to an event-driven consumer

What is publish-subscribe?

Publishers anonymously broadcast messages onto the
network. Subscribers anonymously receive messages.

What is subject-based addressing?

Subject-based addressing directs messages to their destinations so
application processes can communicate without IP addresses or
connections. Subject-based addressing features a set of rules that
defines a uniform name space for messages and their destinations. The
subscriber independently looks for subject names of interest, without
regard for source.

What are the advantages of subject-based addressing?

Subject-based addressing is a more powerful technique than binding
servers to fixed names or addresses, because the mapping from subject
to server is dynamic - each server process listens to a set of
subjects, and handles requests on those subjects.

A server can adapt to changing conditions by changing the subjects to which it listens; it is
thus quite easy to relocate and exchange server applications, and incrementally add
components to a distributed system, without any interruption in service. 

What is location transparency?

Location transparency is the ability of applications to interoperate
without knowledge of physical location, network address, socket
numbers, server identity or other location information. Subscribers
and publishers of information need not know the location of other
subscribers and publishers on the network, resulting in greater
flexibility and scalability.

What is self-describing data?

Self-describing data is data packaged with information that describes
its type, size and name.  



J C Lawrence                               Internet: claw at kanga.nu
----------(*)                             Internet: coder at kanga.nu
...Honourary Member of Clan McFud -- Teamer's Avenging Monolith...

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