Re: Objects and Relations
Date: Sat, 17 Feb 2007 01:02:48 GMT
>>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,
>>- 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
> > > 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
>>>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. After all that time, there has been no mechanistic theory to justify it, just various mumbo-jumbo that appeals to emotion/wishing or involves word games. It seems that some people can never get this. I say fine, recognizing that could help the rest of us save time. A comparison that makes sense to me has to do with electrons. I've been taught in several courses that in an electrical circuit they are capable of moving long distances. I've never been able to believe this, but at the same time have been able to explain circuits to myself as abstractions where the end result can be produced by imagining that they move over long distances rather than just bounce against each other. I wish the "real-world-entity" people would try to explain how a finite machine could identify every electron in the world when it would have to record its own electrons as well. Whereas what's in our heads has no such limits and as long as we agree on some limited and coherent definition of the symbols we want to talk about, we can mimic a fraction of our logic on a digital computer and find that the conclusions we can come up with in our heads seem to hold true for the computer result. We seem to base this faith on induction.
When I see a lot of posts on a thread that I don't understand, one litmus test I (usually) apply is to ignore it if I see a lot of posts from those people who seem to have been born without the abstraction dna gene or molecule or whatever it's called. Not to say they are deficient in every way, after all I'm deficient in lots of ways as I'm regularly told outside of c.d.t.m but their "abstract values" are just as mathematical sets as the ones we try to record with db's. Like all members of sets, they can't identify themselves without outside help, but some of the rest of us think we can identify them. That's life and nature, we are what we are and can't change it.
p Received on Sat Feb 17 2007 - 02:02:48 CET