Alan Kay on OOP

gistfile1.txt

Dr. Alan Kay explains when "object-oriented" was first used and what it means. [] (Meaning of "Object-Oriented Programming" According to Dr. Alan Kay (meaning of OOP objectoriented definition term notion meaning explanation what is)), document, page 721691
http://www.purl.org/stefan_ram/pub/doc_kay_oop_en (permalink) is the canonical URI of this page.
Stefan Ram
Dr. Alan Kay  on the Meaning of “Object-Oriented Programming”
(To link to this page, please use the canonical URI "http://www.purl.org/stefan_ram/pub/doc_kay_oop_en" only, because any other URI is valid only temporarily.)
E-Mail of 2003-07-23
Dr. Alan Kay  was so kind as to answer my questions about the term “object-oriented programming”.
Clarification of "object-oriented" [E-Mail]


Date: Wed, 23 Jul 2003 09:33:31 -0800

To: Stefan Ram [removed for privacy]

From: Alan Kay [removed for privacy]

Subject: Re: Clarification of "object-oriented"

[some header lines removed for privacy]

Content-Type: text/plain; charset="us-ascii" ; format="flowed"

Content-Length: 4965

Lines: 117



Hi Stefan --



Sorry for the delay but I was on vacation.



At 6:27 PM +0200 7/17/03, Stefan Ram wrote:

>   Dear Dr. Kay,

>

>   I would like to have some authoritative word on the term

>   "object-oriented programming" for my tutorial page on the

>   subject. The only two sources I consider to be "authoritative"

>   are the International Standards Organization, which defines

>   "object-oriented" in "ISO/IEC 2382-15", and you, because,

>   as they say, you have coined that term.



I'm pretty sure I did.



>

>   Unfortunately, it is difficult to find a web page or source

>   with your definition or description of that term. There are

>   several reports about what you might have said in this regard

>   (like "inheritance, polymorphism and encapsulation"), but

>   these are not first-hand sources. I am also aware that later

>   you put more emphasis on "messaging" - but I still would like

>   to know about "object oriented".

>

>   For the records, my tutorial page, and further distribution

>   and publication could you please explain:

>

>     When and where was the term "object-oriented" used first?



At Utah sometime after Nov 66 when, influenced by Sketchpad, Simula, 

the design for the ARPAnet, the Burroughs B5000, and my background in 

Biology and Mathematics, I thought of an architecture for 

programming. It was probably in 1967 when someone asked me what I was 

doing, and I said: "It's object-oriented programming".



The original conception of it had the following parts.



  - I thought of objects being like biological cells and/or individual 

computers on a network, only able to communicate with messages (so 

messaging came at the very beginning -- it took a while to see how to 

do messaging in a programming language efficiently enough to be 

useful).



  - I wanted to get rid of data. The B5000 almost did this via its 

almost unbelievable HW architecture. I realized that the 

cell/whole-computer metaphor would get rid of data, and that "<-" 

would be just another message token (it took me quite a while to 

think this out because I really thought of all these symbols as names 

for functions and procedures.



  - My math background made me realize that each object could have 

several algebras associated with it, and there could be families of 

these, and that these would be very very useful. The term 

"polymorphism" was imposed much later (I think by Peter Wegner) and 

it isn't quite valid, since it really comes from the nomenclature of 

functions, and I wanted quite a bit more than functions. I made up a 

term "genericity" for dealing with generic behaviors in a 

quasi-algebraic form.



  - I didn't like the way Simula I or Simula 67 did inheritance 

(though I thought Nygaard and Dahl were just tremendous thinkers and 

designers). So I decided to leave out inheritance as a built-in 

feature until I understood it better.



My original experiments with this architecture were done using a 

model I adapted from van Wijngaarten's and Wirth's "Generalization of 

Algol" and Wirth's Euler. Both of these were rather LISP-like but 

with a more conventional readable syntax. I didn't understand the 

monster LISP idea of tangible metalanguage then, but got kind of 

close with ideas about extensible languages draw from various 

sources, including Irons' IMP.



The second phase of this was to finally understand LISP and then 

using this understanding to make much nicer and smaller and more 

powerful and more late bound understructures. Dave Fisher's thesis 

was done in "McCarthy" style and his ideas about extensible control 

structures were very helpful. Another big influence at this time was 

Carl Hewitt's PLANNER (which has never gotten the recognition it 

deserves, given how well and how earlier it was able to anticipate 

Prolog).



The original Smalltalk at Xerox PARC came out of the above. The 

subsequent Smalltalk's are complained about in the end of the History 

chapter: they backslid towards Simula and did not replace the 

extension mechanisms with safer ones that were anywhere near as 

useful.



>

>     What does "object-oriented [programming]" mean to you?

>     (No tutorial-like introduction is needed, just a short

>     explanation [like "programming with inheritance,

>     polymorphism and encapsulation"] in terms of other concepts

>     for a reader familiar with them, if possible. Also, it is

>     not neccessary to explain "object", because I already have

>     sources with your explanation of "object" from

>     "Early History of Smalltalk".)



(I'm not against types, but I don't know of any type systems that 

aren't a complete pain, so I still like dynamic typing.)



OOP to me means only messaging, local retention and protection and 

hiding of state-process, and extreme late-binding of all things. It 

can be done in Smalltalk and in LISP. There are possibly other 

systems in which this is possible, but I'm not aware of them.



Cheers,



Alan



>

>   Thank you,

>

>   Stefan Ram





-- 

E-Mail of 2003-07-26
Clarification of "object-oriented", 1 [E-Mail]


Date: Sat, 26 Jul 2003 13:47:59 -0800

To: Stefan Ram [removed for privacy]

From: Alan Kay [removed for privacy]

Subject: Re: Clarification of "object-oriented"

[some header lines removed for privacy]

Content-Type: text/plain; charset="us-ascii" ; format="flowed"

Content-Length: 3145

Lines: 68



One of the things I should have mentioned is that there were two main 

paths that were catalysed by Simula. The early one (just by accident) 

was the bio/net non-data-procedure route that I took. The other one, 

which came a little later as an object of study was abstract data 

types, and this got much more play.



If we look at the whole history, we see that the proto-OOP stuff 

started with ADT, had a little fork towards what I called "objects" 

-- that led to Smalltalk, etc.,-- but after the little fork, the CS 

establishment pretty much did ADT and wanted to stick with the 

data-procedure paradigm. Historically, it's worth looking at the USAF 

Burroughs 220 file system (that I described in the Smalltalk 

history), the early work of Doug Ross at MIT (AED and earlier) in 

which he advocated embedding procedure pointers in data structures, 

Sketchpad (which had full polymorphism -- where e.g. the same offset 

in its data structure meant "display" and there would be a pointer to 

the appropriate routine for the type of object that structure 

represented, etc., and the Burroughs B5000, whose program reference 

tables were true "big objects" and contained pointers to both "data" 

and "procedures" but could often do the right thing if it was trying 

to go after data and found a procedure pointer. And the very first 

problems I solved with my early Utah stuff was the "disappearing of 

data" using only methods and objects. At the end of the 60s (I think) 

Bob Balzer wrote a pretty nifty paper called "Dataless Programming", 

and shortly thereafter John Reynolds wrote an equally nifty paper 

"Gedanken" (in 1970 I think) in which he showed that using the lamda 

expressions the right way would allow data to be abstracted by 

procedures.



The people who liked objects as non-data were smaller in number, and 

included myself, Carl Hewitt, Dave Reed and a few others -- pretty 

much all of this group were from the ARPA community and were involved 

in one way or another with the design of ARPAnet->Internet in which 

the basic unit of computation was a whole computer. But just to show 

how stubbornly an idea can hang on, all through the seventies and 

eighties, there were many people who tried to get by with "Remote 

Procedure Call" instead of thinking about objects and messages. Sic 

transit gloria mundi.



Cheers,



Alan



At 10:05 PM +0200 7/26/03, Stefan Ram wrote:

>On Wed, Jul 23, 2003 at 09:33:31AM -0800, Alan Kay wrote:

>>  OOP to me means only messaging, local retention and protection and

>>  hiding of state-process, and extreme late-binding of all things.

>

>   Hi Alan,

>

>   I just want to say "thank you" for your explanations

>   (including the parts not quoted above)!

>

>   "local retention" is a new notion to me in the context

>   of OOP, and I assume it refers to state-process and

>   means that an object is in possession of its state-process,

>   so that the state of an object is kept locally with the

>   object and not elsewhere.

>

>   I have published your reply on the web, but have removed

>   the E-Mail addresses and similar header lines for privacy.

>

>   Thanks again,

>

>   Stefan





-- 

Remarks
A memorandum on dataless programming:
http://www.rand.org/pubs/research_memoranda/2007/RM5290.pdf
Other Pages of this Site
Examples of some other (German language) pages of this site:
>720702 objektorientierte Programmierung
>721677 Programmiersprache
>720866 Kurse (Orte und Zeiten)
>720873 Lehrgang Aktiv programmieren lernen mit Java
>720872 Lehrgang Aktiv programmieren lernen mit C++
>721701 Rechtschreibreform, Schulsprache
ASCII-Tabelle JavaScript

About this page, Impressum  |   Form for messages to the publisher regarding this page  |   "[email protected]" (without the quotation marks) is the email-address of Stefan Ram.   |   Beginning at the start page often more information about the topics of this page can be found. (A link to the start page appears at the very top of this page.)  |   Copyright 2004 Stefan Ram, Berlin. All rights reserved. This page is a publication by Stefan Ram. Stefan Ram Berlin slrprd slrprd stefanramberlin spellched stefanram721691 stefan_ram:721691 slrprd, slrprdqxx, slrprddoc, slrprd721691, slrprddef721691, PbclevtugFgrsnaEnz