What's a POS??

William A. Barnett-Lewis wlewis@mailbag.com
Thu, 08 May 1997 22:33:50 -0500

At 07:20 PM 5/8/97 -0700, you wrote:
>  It seems in this discussion about POSes, everyone is assuming that a
>PSO is whatever they've always assumed a POS was. The rest of us
>haven't the foggiest idea what YOU mean by a POS. So here's some
>questions about POSes that I'd like you guys to answer so we can
>figure out what your POS is.

Hmm...Good point.

>Is a POS completely transparent to the programmer and user? The old
>Xerox Interlisp machines used something like this. You just did your
>mornal lisp things and then the system saved everything for the next
>time you came back around. This is the dumplisp/checkpoint approach.
>How fine a granularity does your checkpointing have? How do you handle
>different things wanting different granularities?

To me, the POS should be, essentially, transparent. You utilize it the way
that in a unix system you use the filesystem. In a way, the Interlisp
approach is crossed with the SHORE oodbms approach. Each GC would also make
an implicit partial "dumplisp" to a "temporary" persistant store of those
things that have
changed in your world. These changes would be promoted to "permanent"
persistancy when you did a concious save of your changes. This promotion
would be handled the same way that generational gc handles promotion of
The old Interlisp approach isn't really that bad to begin with. Using a ore
explicitly oo aproach  to reimplimenting it might take care of the hassles
that remain.

>If not the above, then does the object builder or the object user
>determine if the object is persistant? Ie, does the object have to be
>a special kind of object (maybe a CLOS object with a particular base
>class) or can I tell the POS system to "save" any ole object?

Then you have a database rather than a store; which may "Be" what people want...

>If it's the latter, how do you determine where the object ends and
>some other object begins? If you aren't careful, you're going to
>implement dumplisp. :-)
> Thanks for the info,
>  Mike McDonald
>  mikemac@engr.sgi.com

William Barnett-Lewis
William A. Barnett-Lewis
"We are artists.  Poets paint motion  and light.  Historians paint stills.
It can be dangerous to get history from a poet.  It can also be the greatest
						Larry Miller Murdock