Re: Moving Objects

Re: Moving Objects

[S Muralidharan]

Johnson writes:

>Distributed programmers often want to move objects to increase
>efficiency and reliability.  Objects are moved to be close to
>the machine that is using them, and to get off of a machine that
>is going down.  This has nothing to do with reusability or
>object-oriented doctrine.

I believe concerns of software reusability definitely play a crucial
role in determining what is efficient and what is not, in a distributed
system. Consider the following argument.

The efficiency of moving an object depends, for example, on some of the
following factors: the representation of the object, the distribution
of the sub-objects of the object, the sizes of the object/sub-objects,
and the hardware architecture. (Note: a sub-object may have sub-objects.)

If software reusability based on the specifications of objects is a
concern, neither the developer of an object nor a client can make
an independent decision on what to move or how to move, or how much to move,
to achieve optimal efficiency. Whatever the reasons for object movement,
they will certainly be influenced by the concerns of specification-based
software reusability.

Though I do not know the issues in distributed system reliability, I can
believe that reliability need not necessarily be achieved through
object movement.

Cheers,

Murali

Re: Moving Objects

[Tim King]

In article <59237@tut.cis.ohio-state.edu>, murali@coracle.cis.ohio-state.edu
(S Muralidharan) writes:

> I believe concerns of software reusability definitely play a crucial
> role in determining what is efficient and what is not, in a distributed
> system. Consider the following argument.
> 
> The efficiency of moving an object depends, for example, on some of the
> following factors: the representation of the object, the distribution
> of the sub-objects of the object, the sizes of the object/sub-objects,
> and the hardware architecture. (Note: a sub-object may have sub-objects.)
> 
> If software reusability based on the specifications of objects is a
> concern, neither the developer of an object nor a client can make
> an independent decision on what to move or how to move, or how much to move,
> to achieve optimal efficiency. Whatever the reasons for object movement,
> they will certainly be influenced by the concerns of specification-based
> software reusability.

I agree that neither the client nor the developer of an object has sufficient
information to effectively migrate objects, and reuse is a key issue here.  In
the absence of a distributed object management system, you could let the user
or developer make the choices and take the chances, or you could punt on
object migration.  All of these approaches have drawbacks.  However, *if* (and
this is a big if) you had an underlying distributed OMS, it *would* have the
information necessary to decide when and where to migrate objects, and object
migration would have little to do with reusability.

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