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Re: Reflective systems

From: S. Alexander Jacobson <alex@shop.com>
Date: Tue, 5 Feb 2002 15:44:13 -0500 (EST)
To: Marwan Sabbouh <ms@mitre.org>
cc: Kurt Cagle <kurt@kurtcagle.net>, <xml-dist-app@w3.org>, "John J. Barton" <John_Barton@hpl.hp.com>
Message-ID: <Pine.WNT.4.43.0202051543320.1556-100000@gandolph.ASGARD.jms>
Why is an inheritance hierarchy important as
distinct from just type labeling.
For example, MIME content-types don't have an
explicit inheritance system but they work really
well for email and HTTP transactions.

-Alex-

On Tue, 5 Feb 2002, Marwan Sabbouh wrote:

> Sorry,  I think I phrased it wrong.  I did not mean the "is a necessary ..."  The point I was trying to make is: if you have the inheritance tree on the wire (see the ILU from Xerox PARC), it made it easy for me to implement reflections in a manner independent of the programming language.  nor did I imply that reflective is self descriptive or anything like that.  Thank you
>
> Marwan
>   ----- Original Message -----
>   From: John J. Barton
>   To: Marwan Sabbouh ; Kurt Cagle ; xml-dist-app@w3.org
>   Sent: Tuesday, February 05, 2002 12:53 PM
>   Subject: Re: Reflective systems
>
>
>   Ok hold on here.  Reflective systems do not require
>   strong typing: see for example Smalltalk:
>   "Reflective Facilities in Smalltalk-80"
>   Brian Foote, Ralph E. Johnson, OOPSLA 1989
>   http://www.laputan.org/ref89/ref89.html
>   or
>   Smalltalk: a Reflective Language
>   Fred Rivard
>   http://www.emn.fr/cs/object/biblio/publications/reflection96/reflection96.html
>   (Smalltalk being the arch-typical *not* strong-typed language).
>
>   And reflective is not self-descriptive.  "Reflective" is reasonably
>   well defined in programming-language land.  Self descriptive is
>   somewhat less well defined as I understand it, but most importantly
>   the term refers messages not programming languages.  You can
>   have a reflective distributed system without self-descriptive
>   messages and a non-reflective distributed system with
>   self-descriptive messages.
>
>   I don't want to start a whole debate on this but neither should
>   we be mixing apples and crankshafts.
>
>   John.
>
>   At 08:20 AM 2/5/2002 -0500, Marwan Sabbouh wrote:
>
>     In my previuos research on middleware, I found that strong typing is a
>     necessary condition for reflective systems.  Strong typing means that the
>     inheritance tree is sent with every method invocation.  In this way, RDF may
>     have much value to add beyond just interfaces.  Actually, RDF is at the
>     heart of everything I am doing at the moment, and it is proving extremely
>     useful.  ( I am hoping to get a paper out soon on RDF)
>
>     Marwan
>
>     ----- Original Message -----
>     From: "Kurt Cagle" <kurt@kurtcagle.net>
>     To: <xml-dist-app@w3.org>
>     Sent: Tuesday, February 05, 2002 2:14 AM
>     Subject: Re: Reflective systems
>
>
>     > I'm jumping into this in the middle, so may be missing something, but I
>     > would concur with the assessment that one primary disadvantage that binary
>     > RPC mechanisms have is their inate inability to be self-descriptive. The
>     > IDispatch mechanism works effectively if you have an IDL, but if you don't
>     > then you're basically stuck in the dark about the characteristics of an
>     > object (especially, as with many scripting interfaces, the core object
>     only
>     > acts as a proxy mechanism). The power of XML is not only that you can have
>     a
>     > descriptive interface, but you can in fact have any number of them - XSD,
>     > RDF, WSDL, XTM, depending upon your requirements, and you can also utilize
>     > multiple interface descriptors simultaneously.
>     >
>     > ----- Original Message -----
>     > From: "Mark Baker" <distobj@acm.org>
>     > To: "Rich Salz" <rsalz@zolera.com>
>     > Cc: "Williams Stuart" <skw@hplb.hpl.hp.com>; <xml-dist-app@w3.org>
>     > Sent: Monday, February 04, 2002 3:06 PM
>     > Subject: Reflective systems
>     >
>     >
>     > > >
>     > > > > Absolutely true.  The wonderful thing about the Web is that this is
>     > done
>     > > > > *with* the Web.  It can describe itself.  RPC cannot.
>     > > >
>     > > > I disagree. Adding RDF to the web and saying it's reflexive seems no
>     > > > different from adding DII to Corba, IDispatch to COM, etc.
>     > >
>     > > I don't know about IDispatch, but IIRC, DII did not reify interfaces as
>     > > first class objects (i.e. they didn't get OIDs).
>     > >
>     > > Also, while that's necessary, it's not sufficient.  What's also needed
>     > > is a uniform means of resolving an identifer.  Neither CORBA nor COM
>     > > has that, but the Web has GET.
>     > >
>     > > MB
>     > > --
>     > > Mark Baker, Chief Science Officer, Planetfred, Inc.
>     > > Ottawa, Ontario, CANADA.      mbaker@planetfred.com
>     > > http://www.markbaker.ca  http://www.planetfred.com
>     > >
>     > >
>     >
>     >
>
>
>   ______________________________________________________
>   John J. Barton          email:  John_Barton@hpl.hp.com
>   http://www.hpl.hp.com/personal/John_Barton/index.htm
>   MS 1U-17  Hewlett-Packard Labs
>   1501 Page Mill Road              phone: (650)-236-2888
>   Palo Alto CA  94304-1126         FAX:   (650)-857-5100
>

___________________________________________________________________
S. Alexander Jacobson                   i2x Media
1-212-787-1914 voice                    1-603-288-1280 fax
Received on Tuesday, 5 February 2002 16:28:54 GMT

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