Applications Messaging Standard

[Doug Tody]

On Thu, 8 Feb 2007, Alasdair Allan wrote:
>> Is PLASTIC a messaging protocol or a messaging infrastructure?
>
> Both, PLASTIC applications pass a message either using Java-RMI or XML-RPC to 
> the PLASTIC Hub which passes the message out to applications that have 
> registered that they deal with that message either using Java-RMI or XML-RPC 
> depending on which the application supports. [...]
>
>> That is, if I already have a robust messaging infrastructure, can I layer a 
>> PLASTIC adapter on top of this and achieve the same level of 
>> interoperability between applications as with the simple PLASTIC hub? 
>> PLASTIC apps would still "speak" PLASTIC, but the messaging infrastructure 
>> could be anything.
>
> Sort of...

In any case, the real issue here is not what the current PLASTIC 
implementation does, but what we want for an inter-tool messaging
standard developed via the IVOA framework.

I suggest that this should:

     o	Target simple inter-tool messaging (don't try to be a full
     	messaging infrastructure; that is a separate problem).

     o	Separate protocol from implementation.  That is, we should be
     	able to implement a message bus/hub in different languages such
 	as Java or C, or layer the protocol on top of an existing robust
 	messaging infrastructure such as D-Bus, MPI, PVM, ActiveMQ,
 	Ice, CORBA, etc.  It is fine to have a simple hub (or two)
 	developed as part of the standard, which doesn't queue messages,
 	guarantee delivery, and so forth.

     o	Separate protocol from message content.  The message content can
     	be defined/standardized separately.  It should be possible to
 	easily extend the protocol by adding new message content.

     o	Be multi-language and not tied to any one messaging technology
     	(such as Java RMI).

     o	Be multi-protocol, with the same message content expressable
 	in at least two different wire protocols (XML/RPC, JSON,
 	OpenWIRE, STOMP, etc.).

A concern is that, if in the future we try to use this inter-tool
messaging standard in distributed data analysis system which already
has a robust general messaging infrastructure, it should be possible
to layer the inter-tool protocol on top of this infrastructure,
without having to support two similar but different implementations.

 	- Doug