Re: Mixing OO and DB

From: Brian Selzer <brian_at_selzer-software.com>
Date: Tue, 19 Feb 2008 05:19:38 GMT
Message-ID: <KFtuj.12365$R84.5905_at_newssvr25.news.prodigy.net>


"JOG" <jog_at_cs.nott.ac.uk> wrote in message news:81031d4e-3fa2-413c-a38b-1620fa22484a_at_i12g2000prf.googlegroups.com... On Feb 18, 2:54 pm, "Brian Selzer" <br..._at_selzer-software.com> wrote:
> "JOG" <j..._at_cs.nott.ac.uk> wrote in message
>
> news:9098871a-bd2c-4385-b547-542f38b2055a_at_34g2000hsz.googlegroups.com...
>
>
>
> > On Feb 15, 2:31 am, David BL <davi..._at_iinet.net.au> wrote:
> >> On Feb 14, 10:38 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
> >> [snip]
> >> > On Feb 14, 3:52 am, David BL <davi..._at_iinet.net.au> wrote:
> >> > "todays lottery numbers: 23, 34, 17"
> >> > "experimental results: 23, 34, 17"
>
> >> > All written down on a bit of paper - same values discussed, but
> >> > different data. Agree or disagree?
>
> >> I agree. Yes, same values but different data
>
> >> > I ask this because if we can distinguish data and values, we must
> >> > then
> >> > determine /how/ they are different. You state it is by "encoding" but
> >> > the two lines above are encoded in the same manner as far as I am
> >> > concerned, so that cannot be the difference between the two concepts.
> >> > That is unless your "Encodings" equates to my notion of "Facts", and
> >> > we are thus agreeing loudly, using different definitions of those
> >> > terms.
>
> >> They are the same values and they are encoded in the same manner.
> >> However they are distinct appearances, hence distinct data.
>
> > Ok, so we're agreed at least there. Same values with the same
> > encoding. Yet the first datum is different to the second. The logic
> > below therefore follows:
>
> > 1) The two items of data discussed have the same values and same
> > encoding.
>
> Yes.

Hey Brian. That's good - at least there is consensus there.

>
> > 2) The two items of data can obviously be distinguished (we are agreed
> > they are not the same data).
>
> No. They are the same data.

>>>>>>>>>>>>>>>>>>>>>>>>>>>>

Ok, that I personally find a strange use of the term. You seem to be saying that:

P(a, b)
Q(a, b)

is the same data? To me that looks like the first line is a different datum to the second, even though they share the same values. Definitely not in your opinion?

<<<<<<<<<<<<<<<<<<<<<<<<<<<<

Well, the literals a and b are data, each asserting that there is a specific and distinct individual, no matter how many times it appears. The literals, Pab and Qab are also data, each stating that there is a specific and distinct relationship between the specific individuals that map to a and b.

So I guess from one point of view, they are the same data, and from another, they are different data. Sorry for the confusion. I had only the one point of view in mind.

>
> > 3) Therefore a datum must possess some attribute outside of its values
> > and encoding.
>
> Yes, but not what you think: A fact is supposed to be true.
>
> Each appearance of a value in a proposition that is supposed to be true is
> data, but each appearance in the same proposition is the same data.
> But isn't it also true that at least some combinations of values, such as
> those
> combinations of values that appear in a tuple, may also be data?
>
> Let me try to be absolutely clear here:
>
> Let a and b be constant symbols;
> Let x and y be free variables;
> Let P and Q be predicate symbols.
>
> Then if Pxy is a predicate with two free variables that range over the
> same
> domain, then Pab is a literal that can appear in the extension of Pxy by
> substituting the constant a for every appearance of the free variable x in
> P
> and the constant b for every appearance of y.
>
> Let's let constant symbols also be literals.
>
> So b is a literal; Pab is a literal; Pbb is a literal; and so on.
>
> A literal that is supposed to be true is an atomic fact.
>
> Assuming that Pab is supposed to be true, then b indicates that the
> individual that b maps to exists, a indicates that the individual that a
> maps to exists, and Pab indicates that both a and b participate in the
> relationship P. Pab depends upon a and b, but Paa could also be true, and
> so could Pbb, and so could Qab; so it is safe to say that the literals
> Pab,
> Pbb and Qab would only indirectly indicate that the individual that b maps
> to exists, although each would convey a distinct atomic fact concerning
> that
> individual.
>>>>>>>>>>>>>>>>>>>>>>>>>
Ok, riding with it for a moment, If I follow correctly, you are saying that, P(a,b) -> Exists(a) & Exists(b). That certainly seems entirely sensible.

<<<<<<<<<<<<<<<<<<<<<<<<<<<

Not exactly. a and b are constant symbols that map to individuals. Under the unique name assumption, the literals a and b each asserts that there is a specific individual that is distinct from every other individual.

So, Pab --> a /\ b.

>
> Now if Pab appears in a proposition that is not supposed to be true, then
> it
> cannot be determined whether b maps to an individual that exists or that a
> maps to an individual that exists. It may be that they do, but that they
> just don't participate in the relationship, P, or for that matter, it may
> be
> that the literal Pab also appears in a proposition that is supposed to be
> true.

>>>>>>>>>>>>>>>>>>>>>>>>

Yes, in the case ¬P(a,b) no conclusions can be made concerning the existence or non-existence of a and b. That too seems sensible.

<<<<<<<<<<<<<<<<<<<<<<<<

I don't think we're on the same page here. Pab is a literal formed by substituting a for every appearance of the free variable x in P and b for every appearance of y. Pab may appear in any number of propositions, for example,

Paa \/ Pab \/ Qab \/ Qbb,

Pab \/ Pbb \/ Qaa,

or maybe,

Pab \/ Qab.

But at most one of those propositions can be the case at a time.

Pab appears in (Pab \/ Pbb \/ Qaa), but if (Pab \/ Pbb \/ Qaa) is not the case, it can't be determined that a or b or even Pab. My point is that in order to be a fact, the proposition in which the literal appears must also be the case.

In addition, just because the proposition in which Pab appears is not the case doesn't necessarily mean ¬Pab. For example, suppose that the proposition Pab /\ Pbb is not the case, but that the proposition Paa /\ Pab /\ Pbb is the case. ¬(Pab /\ Pbb) cannot mean ¬Pab becasue Paa /\ Pab /\ Pbb --> Pab.

> Whether a literal is supposed to be true depends upon whether the
> proposition it appears in is supposed to be true. So just the appearance
> of
> a value--even in context--isn't necessarily data. The appearance of a
> value
> in a context that is supposed to be true is data.

>>>>>>>>>>>>

Are you proposing then that if ¬P(a, b), then a and b are not data at all?
<<<<<<<<<<<<<<

No, that's not what I'm proposing. Suppose that ¬Pab is true. If either a or b does not denote, then neither does Pab nor does ¬Pab; therefore, if ¬Pab, then since a and b must denote, then both a and b must also be data.

What I'm saying is that in order to be data, a value must appear in a proposition that is supposed to be true. A perfect example is the database that is constructed during an a relational assignment. Until the assignment actually completes, the proposed database and hence the proposition that it represents /can be/ the case, but isn't. Obviously, the current database and the proposed database cannot both represent propositions that are supposed to be true. By completing the assignment, what you're doing is supposing that the proposed database that contains the new relation represents a true proposition while at the same time denying that the current database that contains the old relation represents a true proposition.

>>>>>>>>>>

A concern that jumps into my mind generally about all this (in terms of defining 'data') is that yours a's and b's are individuals, not values. I would never consider individuals (people for example) to be data. But I would consider statements about those individuals to be data. All best, J.
<<<<<<<<<<

My a's and b's are not individuals, they are values--constant symbols that individuals map to. When used as a literal each simply asserts that there is a specific and distinct individual.

>
> It follows then that even though a datum can appear multiple times in the
> same proposition, it is always still the same datum, but that each
> appearance is in addition different data, a predication.
>
> > What one /calls/ that extra component is debatable (context,
> > description, etc), but I cannot see anyway around the above logic - in
> > fact I feel like it is an incredibly strong argument. It starts with
> > agreed observations, followed by the application of the law of
> > indiscernibility of identicals.
>
> > If you can see a hole in it then I'm sure you'll let me know ;)
>
> >> [snip]
> >> > Well put. I contend that you can't do this, and that a poem or image
> >> > as described is not an example of data, but merely values. You are
> >> > saying to me "a poem is data. It is clearly not a fact. Ergo,
> >> > pwnage."
>
> >> In this discussion I would prefer to actually say "the appearance of a
> >> poem is data".
>
> >> > But you are already assuming it is data in the first step. I say its
> >> > not, and cannot follow why you would think it is. Like a "22". That's
> >> > not data but, if I was a numerologist say, I would still find the
> >> > value interesting.
>
> >> I keep thinking you're ignoring my qualification that it is the
> >> appearance of a value that counts as data, not the value itself.
>
> > Not my intention to ignore it, but I have been wary of getting into a
> > more handwavy discussion about nominalism, universals, formalism etc,
> > etc. However, I hope to have shown above that saying data is the
> > merely appearance of a value (and that may well be part of it) is
> > insufficient, and that a datum is made up of the 'appearance of
> > values' /plus/ something else.
>
> >> > So to me the poem is just a value.
>
> >> Yes, but would you say the appearance of a value is just a value?
>
> >> > Its only data when I say this thing
> >> > here, X, has role Y.
>
> >> We agree that a value doesn't have a context. However the appearance
> >> of a value *does* have a context.
>
> > Ok, I understand. I am just saying the context has to be considered as
> > part of the data, not just as a product of it appearing. Again, I
> > hope my previous logic has shown that the data must be considered as
> > possessing an attribute outside of 'a value' and the fact that it
> > appears.
>
> >> > A picture is just a picture. Even if its, say, a
> >> > biochemistry picture of a cell membrane. _However_ if that picture is
> >> > then put in a log book, under "image of neurostem cell from
> >> > experiment
> >> > B", its data. This accords to tradtional definitions.
>
> >> You seem to have three distinct arguments.
>
> >> 1) Data requires knowledge in order to decode it as a value; and
> >> this knowledge is part of the data.
>
> >> 2) David has been saying data = value; and
> >> a value (is just a value and) doesn't have a context; and
> >> a conveyed value without a context is meaningless.
>
> >> 3) by definition data = encoded values that represent facts; so
> >> an encoded poem (with no additional context) is not data
>
> >> Please tell me if I've misrepresented you!
>
> > Hard to tell, I think I've gradually been changing my mind throughout
> > this conversation ;) I certainly feel like I have a stronger argument
> > now to explain what was more of an intuition to begin with. But hey, I
> > try not to be too prissy about this sort of stuff, as I find that I
> > learn more that way.
>
> > My whole argument appears to be now be that you can't externalize the
> > context bit, so I'll leave it at that. Regards, Jim.
>
> >> I would say (1) doesn't actually lead to any differences in practise
> >> over what we call data, making it appear rather metaphysical.
>
> >> In my opinion (2) can be defeated for two different reasons
> >> a) David has actually been saying data = appearance of value; and
> >> an appearance of a value has a context
> >> b) there exists examples (like a poem) where a conveyed value
> >> without any
> >> additional context is useful.
>
> >> (3) leads to a difference on real examples, but I do find it
> >> surprising that I could give you a disk with a web page encoded on it
> >> and you would claim that it isn't actually data (but it may contain
> >> data).
>
> >> > I am offering you examples where you have an item that you would not
> >> > describe as data, and showing how it is turned into something that is
> >> > generally described as data. All best, have found the conversation so
> >> > far well articulated, even if we don't agree.... Jim.
>
> >> Also the conversation has been courteous. Cheers!
Received on Tue Feb 19 2008 - 06:19:38 CET

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