Re: An object-oriented network DBMS from relational DBMS point of view

From: Bob Badour <bbadour_at_pei.sympatico.ca>
Date: Mon, 19 Mar 2007 20:38:13 GMT
Message-ID: <VwCLh.12437$PV3.128659@ursa-nb00s0.nbnet.nb.ca>

Daniel wrote:

> On Mar 19, 2:01 pm, "Alfredo Novoa" <alfred..._at_gmail.com> wrote:
>

>>On 19 mar, 16:48, "Daniel" <danielapar..._at_gmail.com> wrote:
>>
>>>I hope you agree that the concept of an instance of an ADT is
>>>absolutely clear.
>>
>>"Instance" is a synonym of "object" and it has the very same
>>fuzziness.

>
> I'm not referring to intuitive notions, the algebraic specification of
> ADT's is well understood, there's a literature on that subject. If
> you don't have some basic familiarity with that literature and its
> terminology, it's difficult to have a meaningful discussion.

Sadly, the OO world is full of notions that I don't even think rise to the level of intuitive except that everyone internally substitues some intuitive notion of their own for the term at any given time.

>>values can't be created.

>
> I think this statement belongs to the world of intuitive notions
> rather than algebraic specifications, but let me just ask you two
> questions (and they are questions, I'm not trying to make a point):
>
> Are you saying that it is not meaningful to talk about manufacturing a
> custom value as an aggregate of atomic values such as 1.0, "Jun 1,
> 2007", and 33?

"Manufacture" has no clear meaning in the above so no it is not meaningful. You list several literals that could each represent any number of values. One can represent any number of other values using the literals in combination.

> Do you think it is meaningful to talk about storing a value in a
> location in computer memory?

Not really. One actually stores a representation of a value at a memory location. People frequently abbreviate that to the sloppy expression you used in your question, though.

>>Let's see the Java spec again:
>>
>>"A class instance is explicitly created by a class instance creation
>>expression"
>>
>>Like:
>>
>>Point point = new Point(0, 0);
>>
>>Here we have created a variable (instance) named "point" assigning the
>>"ethernal" value Point(0, 0) to it.
>>
>>"point" is an object. Isn't it?

>
> In Java, it would be more accurate to say that point is a variable
> that holds a reference to (the address of) a Point object.

And the thing referenced is nothing more or less than a dynamically allocated variable. Hence, in spite of your earlier claim, you use "object" to mean "variable".

>>>Maybe you can clarify, is "value" typically taken as a primitive
>>>concept, or can it be defined axiomatically?
>>
>>Primitive.

>
> Even so, it might be helpful to enumerate the properties that a thing
> must have to be regarded as value, immutability, etc. Then we can ask
> whether an instance of an ADT satisfies those properties.

An ADT is not a value. A good ADT is a formal specification for representing some set of values and the operations defined on them. Received on Mon Mar 19 2007 - 15:38:13 CDT