1) 27-Mar sowa <sowa@t Questions about OO models in log (1563 chars) 2) 27-Mar sowa <sowa@t Copy of note to Elizabeth Fong (7153 chars)
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As a result of the joint meeting between ANSI X3H4 and X3H7, some questions came up about the use of logic, in particular, conceptual graphs and KIF, for defining object models for OO systems.
Following is a note that I sent to Elizabeth Fong with brief answers to some of the questions. Mike Genesereth and I are planning to attend the next meeting of X3H7 (the ANSI Committee on Object Information Management) on July 20th in Chicago. We will be discussing these and related questions concerning how CGs and KIF could be used in the OO standards efforts.
John Sowa
Message 2 -- ********************* Received: from turtle.mcc.com by sunscreen.mcc.com (4.1/isd-other_921116_15:19) id AA11996; Sat, 27 Mar 93 21:44:47 CST Received: from venera.isi.edu by turtle.mcc.com (4.1/isd-master_921116_15:19) id AA15388; Sat, 27 Mar 93 21:44:39 CST Received: from isd9.isi.edu by venera.isi.edu (5.65c/5.65+local-8) id <AA27600>; Sat, 27 Mar 1993 19:44:23 -0800 Date: Sat, 27 Mar 1993 19:46:39 -0800 Posted-Date: Sat, 27 Mar 1993 19:46:39 -0800 Received: from by isd9.isi.edu (5.65c/4.0.3-4) id <AA01647>; Sat, 27 Mar 1993 19:46:39 -0800 Message-Id: <9303280250.AA03991@turing.pacss.binghamton.edu> Comment: List name: SRKB-LIST (do not use email address as name) Originator: srkb-list@isi.edu Errors-To: neches@isi.edu Reply-To: <sowa@turing.pacss.binghamton.edu> Sender: srkb-list@isi.edu Version: 5.5 -- Copyright (c) 1991/92, Anastasios Kotsikonas From: sowa <sowa@turing.pacss.binghamton.edu> To: Multiple recipients of list <srkb-list@isi.edu> Subject: Copy of note to Elizabeth Fong
>From sowa Sat Mar 27 11:38:45 1993
Received: by turing.pacss.binghamton.edu (4.1)
id AA03656; Sat, 27 Mar 93 11:38:39 EST
Date: Sat, 27 Mar 93 11:38:39 EST
From: sowa <sowa>
To: fong@ecf.ncsl.nist.gov
Subject: Comments on questions about logic and OO models
Cc: sowa
Status: R
Liz,
Following are some comments on questions that arose at the joint meeting of X3H7 and X3H4. Could you please forward this note to your mailing list of X3H7 members.
Thanks, John _____________________________________________________________________
> Why choose one logic system over another?
All systems of first-order logic are exactly equivalent to one another. Therefore, the choice of one or another is purely a matter of personal preference, convenience, availability of tools, etc. However, it is necessary to choose at least one concrete notation in order to have some way of recording and communicating whatever models have been represented.
In order to avoid the so-called "religious wars" between competing systems, we had a meeting of the KIF, CG, and SUMM developers to agree upon a common position: to adopt both the KIF and CG syntaxes, to adopt ontological primitives from SUMM for defining other languages, and to adopt the model theoretic basis of KIF n for a common semantics. Therefore, anything represented in either KIF or CGs could be automatically translated to the other, and either one could use SUMM ontological primitives (or others that may be developed) for representing object models or anything else.
> Why is CG a superior interface?
Conceptual graphs have a graphic interface that many people find very readable. But because of the agreement on KIF, CG, and SUMM, CGs and KIF can be automatically translated to one another, and anyone is free to mix or match CGs and KIF in any combination they find convenient. Furthermore, anyone who prefers to develop a new syntax or adapt an older syntax, such as Z, is welcome to do so, provided that they represent exactly the same semantics.
Therefore, we should ask "Why is the common semantic base of KIF and CGs superior?" That is a very complex question that cannot be answered briefly here, but both Mike Genesereth and I plan to attend the joint X3H4.6 and X3H7 meeting on July 20th, and perhaps we can both clarify the various issues. If I had to give one very short answer, however, I would say that the metalanguage capabilities of KIF and CGs are what makes them very powerful as definitional languages -- that is essential for defining object models, conceptual schemas, and various kinds of logics and programming languages.
> Is CG a tool for specifying object models or is it in competition
> to the OO concept?
In my talk in San Antonio, I showed a simple object model and its representation in conceptual graphs. However, I was not trying to propose any particular object model, but to show how logic, in the form of either KIF or CGs, could be used to define object models. Therefore, I would say that the CG-KIF coalition is a basis for specifying object models, and it is not in competition with any of them.
There were also some interoperability questions that I would like to comment on:
> A subsumption model such as CG is capable of being mapped to
> all models. This approach may not solve the interoperability problems.
A formal definition in terms of CGs, KIF, or any other notation will not, by itself, solve the interoperability problems. But it is a necessary first step towards relating and classifying different models. The matrix of features is useful for an overview of many different models, but it is too simplified to show how the features interact. Two different models may have features with similar names and functions, but the details may make them completely incompatible. Therefore, a formal definition of the various models in logic is a necessary follow-on to the matrix classification and a prerequisite for defining precise groundrules for interoperability.
> Frank Manola and Sandra Heiler of GTE submitted an article on
> "Reduced Instruction Set" or "RISC" object model as an approach
> to interoperable object models.
I would say that this seems to be a step in the right direction, but such a RISC object model must be specified precisely in some language, and a version of logic would be the best candidate for a specification language.
> The translator approach, e.g., Express to C++ translator, is an
> example of interoperability between Express and C++.
Translators are useful when you only have two languages that need to cooperate. But if you have N languages, you need N*(N-1) pairs of translators. That is why X3H4 proposed the subsumption approach as a framework for a large family of interoperating systems.
I would also like to make a comment about C++: More than any other OO language, it is close to being a "RISC" OO language. That means that its own object model is so primitive that it is necessary for anyone who uses C++ to augment it with a library of definitions that make it usable for a particular family of applications. The real object model is therefore C++ as augmented with a particular library.
Therefore, the Express to C++ translator is not an example of interoperability between Express and "bare" C++, but an example of interoperability between Express and C++ augmented with a library of definitions to support the Express object model. If someone else is using C++ with a different library of extensions, they would still be incompatible with the Express object model even though they were using the same underlying language.
The point of this comment is that even if you built N*(N-1) pairs of translators, programs translated to language X from incompatible sources A and B would be just as incompatible on the X platform as they were on their original platforms.
Bottom line: I don't believe that there is any magic answer to interoperability. But I do believe that formal definitions in logic of the various object models together with a subsumption model of the various models would be an important step towards groundrules and conventions for interoperability.
John Sowa