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From: tfrancis@wpi.wpi.edu (Krishan M Nainani)
Newsgroups: comp.lang.ada
Subject: Object passing and interpreting
Message-ID: <3512@wpi.wpi.edu>
Date: 11 Aug 89 05:36:33 GMT
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Reply-To: tfrancis@wpi.wpi.edu (Krishan M Nainani)
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Organization: Worcester Polytechnic Institute, Worcester, Mass.
List-Id: <comp.lang.ada>



Hi Folks,

	Recently, I discovered the following article in C.L.I which 
interested me since this was the type of research that was done a few
years ago in the research lab that I am currently involved with.
For those of you who missed it, here it is:


From: davis@COMMUNITY-CHEST.MITRE.ORG (dave davis)
Subject: Handling objects in a distributed system

--------------------------start of article-------------------------------

Ed Berard poses an issue in dealing with objects in a distributed 
system:  how to send an object to another node.  As Ed suggests, 
one solution is to have the knowledge of all the objects within the 
system be present at each node.  However, this might be inefficient 
in certain cases, and could cause difficulties if we with to create 
new objects dynamically.

I suggest that an approach would be to transmit "installation
instructions" (or template, or frame) with each transmitted object so
that the recieving node only needs to know a general schema for object
installation.  The instructions would have to contain information
about the object's interface, its last state, and enough information
about its structure to recreate it locally.  Assuming for a moment
that all of the objects in our system are created from more primitive
objects the mechanism need only have a representative of each
primitive object on hand, and know how to apply them in a specific
case.  Such a mechanism could also be two-way, translating objects
to/from non-objective representations.  This mechanism might also be
of use in storing and retrieving persistent objects off-line.

=================================================================
Dave Davis
MITRE Corp;
McLean, VA
------------------end of article--------------------------------------


My comments:
	Dave, your idea was implemented here using a DDL (Data 
Description Language) which essentially passed the "type" of the 
object that you wanted to pass. Obviously, the object itself was
passed but the DDL was used to interpret the object. In fact, even
lists (also lists of lists of ...) could be implemented. To my understanding
there were a few papers published on this but I am not sure in which 
journal they were published. In addition to this, this software took care
of sending messages even in a Heterogenous Processor Environment.

	As a result, it is a really valuable tool for my current work.

Krishan Nainani		(reply-to :tfrancis@wpi.wpi.edu)