Re: Mixing OO and DB

On Feb 13, 2:06 am, David BL <davi..._at_iinet.net.au> wrote:
> On Feb 12, 9:53 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
> [snip]
> > Consider /unallocated/ RAM in your PC. Look at 5 contiguous bits at
> > random. Are you telling me that the binary number you are looking at
> > is "data"? I'd accept that it is a value (albeit a meaningless one)
> > but "data"? You really think that?
>
> No I don't.
>
> When data is recorded on some medium there is a lot of implicit
> *knowledge* about how it has been encoded. This knowledge has to
> account for all sorts of details, such as what designates a 1 versus a
> 0. How many bits in a word? What order do they appear in? Is there
> an address bus? How is the address bus organised? The binary
> encoding is only a tiny part of it. Obviously we both agree that all
> that knowledge is implicit in correctly decoding the data.

Yes I broadly agree apart from on one key matter (there's a suprise eh) - "knowledge is implict". I contend the exact opposite, and this is my whole point really. The knowledge required must be explicit. That's what makes otherwise random noise, or values, data. In the case of a scientist log book for example what the data means is explicit in a title at the top of the page or in the scientist's head.

Another example:
"todays lottery numbers: 23, 34, 17"
"experimental reults: 23, 34, 17"

Same values, different data. If you agree with this statement then values != data surely?

>
> Our point of contention is rather that I suggest that most generally
> the data is nothing other than encoded values, and doesn't necessarily
> convey any facts. I'm assuming that the knowledge implicit in the
> encoding of the data is by definition not part of the data itself,
> whereas I think you are suggesting it is part of the data.

Yes I think that's an excellent breakdown. Its all just down to where we draw the lines I guess...
Brian: Data is encoded values. I need to know externally what they represent.
Jim: Data is encoded values plus an denotation of what they represent.

>
> I would prefer to say that the knowledge of the encoding (the
> "protocol") exists independently of the recorded data (or even the
> particular instance of the media it is recorded on). For example I
> don't want to create a new file format for every file.
>
>
>
> > > > > I dispute your premise that the purpose of the data in
> > > > > this case is to state a fact that is known a-priori to be true.
>
> > > > A Datum is a given fact. That's what the word means formally. I have
> > > > said nothing more, and I have no idea what you are on about talking
> > > > about "the purpose of data".
>
> > > Let me use an example: I give you a disk with some data, tell you a-
> > > priori that it records a string, describe the format and you are able
> > > to determine that the recorded value is a poem
>
> > > "Is it binary or is it data?
> > > Is it info or knowledge,
> > > or is it wisdom -
> > > the whole enchilada?"
>
> > Thats a value imo, and its only data if we say "The file myPoem.txt
> > contains 'Is it binary or is it...'".
>
> I don't know what that means or what distinction you are making. I'm
> very suspicious of introducing a proposition that is referring by name
> to the file. Names don't have absolute meaning. What is the context
> for this proposition?
>
> > I do realise that the
> > definitions I am suggesting as formal are at odds to the handy wavy,
> > nebulous way we throw around terms such as 'data', 'data model', etc.
>
> > As proof (!) consider your above example if you placed the poem
> > written on paper in front of me. Are you telling me that is data?
> > Course not, its just a poem written down - a value. So then what is
> > the difference between this and your example on a disk? That its
> > encoded in binary?
>
> Since this is a computer science discussion group I'm happy to narrow
> the definition of data to encodings of values that are intended for
> both reading and writing by a computer.
>
>
>
> > > Note that no additional context has been provided. I would say the
> > > purpose of the data was to convey a value, but not to convey a fact.
>
> > > > > If that is its purpose then it conveys precisely zero information.
>
> > > > > > > We can display
> > > > > > > it. We can comment on whether we like it - even if we haven't a clue
> > > > > > > where it came from. But I don't see any sense in which the image
> > > > > > > value gives us any statements of fact beyond the specification of a
> > > > > > > value. A value simply "is".
>
> > > > > > > I would suggest that a lot of the data in the world is characterised
> > > > > > > more closely as "interesting values" than collections of
> > > > > > > propositions.
>
> > > > > > You cannot store these interesting values without implicitly stating
> > > > > > some fact about them.
>
> > > > > By definition, when a value is specified, its type is specified as
> > > > > well (except possibly if type inheritance is supported).
>
> > > > > C. Date states the following in "Introduction to Database Systems",
> > > > > section 5.2, and subsection titled "Values and Variables are typed":
>
> > > > > "Every value has ... some type...Note that,
> > > > > by definition, a given value always has
> > > > > exactly one type, which never changes.
> > > > > [footnote: except possibly if type
> > > > > inheritance is supported]"
>
> > > > > When a particular value like the integer 73 is specified, there is no
> > > > > implicit fact being specified. The statement that the integer 73
> > > > > exists in any absolute sense is entirely metaphysical and meaningless
> > > > > within computer science.
>
> > > > So you just wriite "73" down and are telling me its a datum? I'm
> > > > pretty sure that's what we call a "value", not data.
>
> > > C.Date distinguishes between a value (that by definition doesn't exist
> > > in time and space), versus the *appearance* of a value which appears
> > > in time and space and is encoded in a particular way.
>
> > Is this what your view of the terms is based upon?
>
> These definitions seems reasonable to me.

This seem overly philosophical to me. Surely we don't need metaphysics to know that if someone hands me a bit of paper with: "1.00, 0.376 and 0.904" on it, well that's just a list of values. However if if someone hands you a bit of paper with "Surface Gravity - Earth:1.00, Mars: 0.376 and Venus:0.904", or tells you those denotations, then we have data ;)

>
> I don't agree with everything Date says. For example Date defines
> "data" in the same way you do!

Lol. And me neither, so that's not a good sign. That whole "a relation has a header object" m'larkey for a start. Regards, J.

>
> > > I would suggest that data should by definition be regarded as
> > > synonymous with the appearance of a value.
>
> > > If you don't agree with that, then let's treat it as a definitional
> > > matter. However I'm curious to know what you would say is the
> > > distinction.
>
> > Yes, sure, this is just definitional. However I am on the side of
> > traditional scientific notion of data ("On the third experiment the
> > electrical current was x amps"), as well as Codds! Regards, J.
>
> I agree that most scientific data consists of facts. However you seem
> to have agreed that a poem is a value, and that a poem encoded on a
> disk can be regarded as data.
> I realise that skips past the point you
> want to make, but I thought it had nothing to do with the difference
> between scientific or poetry application domains.
Received on Wed Feb 13 2008 - 13:56:08 CET