Apps messaging discussions

[Doug Tody]

Hi All -

It is good to see the messaging discussion going again, and getting
into important topics such as the message content, message semantics,
message concepts, the messaging protocol, messaging patterns and
use-cases, etc.  However, the discussion is all over the place,
mixing all these things, and discussing both high level issues and
low level details at the same time.  It is difficult to participate
without merely responding to random points.

I suggest trying to organize the discussion into more-or-less separate
topics so that we are not talking about everything at once.  We already
talked a bit about the following:

     o	Scope (simple inter-tool/app messaging).
     o	Overall architecture (separate interface from implementation, etc.)
     o	Basic messaging system ("hub") functionality.
     o	Connnection protocol.

For this next bit how about the following topics:

     o	Messaging model.  Mike made a good start at this.  What is a
 	message, what are the major types of messages at the system
 	level (notify, request, asynchrony, etc.), and what are the
 	standard attributes of a message?  This defines the abstraction
 	within which message content is defined.

     o	Messaging protocol.  John made a good start at this.  What is
 	the interface/protocol used to send and receive messages?
 	How is security handled, if it is handled at all?  This defines
 	how we map the messaging model into an actual messaging
 	protocol (defined independently of implementation of course).

     o	Message content (possibly including use-cases).  Everyone
 	agrees that this is application-specific, can be high or low
 	level, that different schemes can be based on very different
 	approaches and concepts, and should be defined separately
 	from the basic messaging mechanism.

The messaging model is probably the most fundamental.  Message content is
probably the most critical to determine how applications can interact.

Unfortunately, even for a simple but general messaging mechanism, I
think one needs to consider all these things.  The main simplification
is likely to come in the functionality defined by the final
specification, particularly in terms of the messaging protocol and
message content.

 	- Doug