Re: Objects and Relations
Date: 16 Feb 2007 20:04:31 -0800
On Feb 17, 10:02 am, paul c <toledobythe..._at_oohay.ac> wrote:
> JOG wrote:
> > On Feb 16, 4:40 am, Joe Thurbon <use..._at_thurbon.com> wrote:
> >>David BL wrote:
> >>PMFJI, but I think there is an essentially definitional misunderstanding
> >>here. Although, you know, I'm only new at this, so take it with a grain
> >>of salt. I'm really interrupting to see if I'm getting a better
> >>understanding of all this, and I do so with some trepidation.
> >>The word that I think is being used extremely loosely is 'entity'.
> >>In your post you use it to describe, variously,
> >>- integers,
> >>- relations,
> >>- elements of any set,
> >>- things that we want to model with a relational theory*
> >>and a term that can be used to describe anything is basically useless.
> >>*BTW, I'm using theory here in the sense of a logical theory, i.e. a set
> >>of constants, functions, domains, etc. In this post, I'll not use theory
> >>in any other sense.
> >>I'm pretty sure that Jim is using 'entity' to describe 'things that we
> >>might agree exist in the real world', or at least, things outside the
> >>relational theory at hand. An in particular, I think that things that
> >>exist within the theory are not entities, by definition.
> >>Although Jim should feel free to correct me if I'm putting words into
> >>his mouth.
> > No you are pretty much on the money there imo Joe.
> > I am happy to put up with the definition of an entity describing a set
> > of attributes/value pairs. All I object to is the concept that these
> > sets are anything but arbitrary collections.
> > To some people a 'book' requires an attribute stating whether it is a
> > hardback or a softback. In other contexts a book might just be
> > composed of its title, its content, etc. (a book published online
> > perhaps). Please don't dwell on this example, it is just off the top
> > of my head to show that 'entities' are artifices and vary incredibly
> > from person to person and context to context. So as far as data
> > management is concerned, keep 'entities' out, and let humans resolve
> > such concepts outside of the logical model.
> >>>The word "exists" appears a lot in mathematics. For example consider
> >>> P = there exists nonzero integers x,y,z such that x^2 + y^2 = z^2
> >>Loosely, I think that P should be understood as a sentence in a formal
> >>system; one that has a fixed interpretation. In particular, the
> >>interpretation of terms like 'integers', '^', '+' etc, are all fixed
> >>within that formal system. So, 'integers' within the theory would
> >>contain constants like '0', '1' and '2' (which are also within the
> >>theory) that are intended to represent zero, one, two (which are more
> >>nebulous things (possibly entities) that exist outside the theory).
> >>For the theory to be considered good, we'd like those constants to have
> >>provable properties which accord with observable phenomena, like 'I have
> >>one apple, and give you one apple, how many apples do I have?'. My
> >>observation says I have zero apples, and my theory says I have '0'
> >>apples. Phew, my interpretation maps from '0' to zero, so my theory is good.
> >>However, it is important to note that there is no interpretation defined
> >>within a relational theory. So, any interpretation (for example from the
> >>string "12345" within the theory to my particular tax file number)
> >>necessarily happens outside the relational model. In that sense,
> >>entities play no role within a relational theory. And even more
> >>particularly, there is no requirement that things within the theory are
> >>interpreted at all. That is, you can have a relational theory which does
> >>not require you to believe in entities at all.
> >>I think the cornerstone of this misunderstanding is that you have been
> >>using the term entities to describe both things outside and things
> >>inside a relational theory. I'm pretty sure that's not the standard
> >>convention, at least within comp.databases.theory.
> >>>Generally speaking mathematicians don't waste time arging about
> >>>whether the integers exist. Instead they assume it,
> >>I normally wouldn't quibble with this terminology, but to prove a
> >>sentence like 'P' above, mathematicians only assume integers exist in as
> >>much as they are defined within the formal system in which the proof of
> >>P is going to be carried out. They don't really care if one and two
> >>exist, only '1' and '2'.
> >>>and ask more
> >>>refined questions about existence like the one above. In this case P
> >>>is true.
> >>>Now if one believes that the integers don't exist at all then clearly
> >>>P will be false.
> >>If integers don't exist within the formal system above, P is not even
> >>well formed. If integers don't exist outside the formal system above,
> >>then it has not bearing on P's truth or falsehood within the system.
> >>>Is such a philosophical position tenable for a
> >>>mathematican? No! This makes me think mathematicians have a Platonic
> >>>view whether they admit it or not.
> >>I don't think it's relevant.
> >>[... Rest snipped ... ]
> >>As I said above, I'm pretty new at the relational model stuff. I'd be
> >>interested in feedback.
> Nobody asked me, but I think everybody should agree to stop this thread
> as it gets into matters which humans are obviously incapable of. (Being
> as religious as they seem to be, it amazes me how some posters can
> persist in such arrogance, and me being rather atheistic, I think I
> qualify as objective in this case.)
> Although I don't feel capable of re-phrasing everything JOG and Joe T
> have said, I think they understand the essential ingredient for using a
> db for recording, abstraction. Really not a new idea, an Anglo
> renaissance philosopher, John something or other, talked about it
> (sorry, I forget his surname). It seems some people will never get this
> as long as they live (which I think is okay as they will eventually
> desist). What we express via a computer is never real because we agree
> to conditions that allow us to suspend certain details in order to have
> a common abstraction or metaphor. The introduction of the very word
> "entity" thirty or so years ago was a most unfortunnate event.
I don't believe you understand my pov. Abstraction has nothing to do with it. Nouns are used for expressing a wide spectrum of "levels of abstraction". In fact I would say that distinguishing real things versus abstract things is meaningless. I just say nouns (and the entities that they stand for) are important to how the mind works.
[snip] Received on Sat Feb 17 2007 - 05:04:31 CET