Re: Surrogate Keys: an Implementation Issue

"paul c" <toledobythesea_at_oohay.ac> wrote in message news:mJ6zg.277632$Mn5.224019_at_pd7tw3no...
> Brian Selzer wrote:

>> "paul c" <toledobythesea_at_oohay.ac> wrote in message 
>> news:qt4zg.281144$IK3.267521_at_pd7tw1no...
>>> Brian Selzer wrote:
>>>> "paul c" <toledobythesea_at_oohay.ac> wrote in message 
>>>> news:zTOyg.269253$IK3.233927_at_pd7tw1no...
>>>>> Brian Selzer wrote:
>>>>>> "paul c" <toledobythesea_at_oohay.ac> wrote in message 
>>>>>> news:g9Nyg.263082$iF6.250988_at_pd7tw2no...
>>>>>>> Brian Selzer wrote:
>>>>>>>> What's the point of a database if it doesn't reflect some aspect of 
>>>>>>>> reality. ...
>>>>>>> To talk precisely about whatever we want to talk about.  Nothing 
>>>>>>> more. Doesn't need to be real.
>>>>>>>
>>>>>> Agreed.  But even a conceived universe subsumes certain absolutes, 
>>>>>> such as time.
>>>>>>
>>>>> In that case, the statements in the database should talk about time, 
>>>>> ie., aspects of time.  These are different from statements about the 
>>>>> time it takes the database to say something.
>>>>>
>>>> There can be no discussion without time.  Relational assignment cannot 
>>>> exist without the concepts of before and after. ...
>>> For some people, unfortunately, that is a matter of belief.  In the 
>>> context of RT, I'd say it is mere willfullness.  To see why, try to 
>>> avoid the words 'before' and 'after', using say, x and y instead to 
>>> stand for two relations (which  might be the same).  To ask which one 
>>> (or two) does the db state at this moment in time is the same as asking 
>>> does it state x or does it state y.  But to ask which one(s) was stated 
>>> yesterday requires that we deliberately add time information.  This is a 
>>> choice that allows us to ask the second question.  The point is that we 
>>> may not be interested in the second question and choose not to state 
>>> information about time which makes the use of a time concept arbitrary.
>>>
>>
>> But the assignment operation by its nature determines the order of the 
>> states x and y: one must always precede the other because the operation 
>> itself produces that other.
>> ...
>

You're probably right. I generally visualize a discussion as an interplay between participants in a definite sequence, rather than applying a set of rules to the superset of all possible database states and coalescing around the one that meets that criteria.

>
>>> Maybe the confusion arises from Codd mentioning 'time-varying 
>>> relations'. In the interest of making his main points in an efficient 
>>> way, I suspect he didn't want to dot every last 'i'.  As soon as you 
>>> talk about relational assignment you are talking about variable 
>>> replacement, aka pointer replacement.  Logical replacement doesn't 
>>> require any notion of time.  Nor does algebraic difference.
>>>
>>
>> Could you please elaborate on that?  Replacement, as I understand it, 
>> subsumes that something exists and will be superceded by something else. 
>> Algebraic difference isn't even related to assignment.  Difference is an 
>> operator, assignment is an operation.  I don't understand why you 
>> included it.  Perhaps you're conflating the concepts of operator and 
>> operation.
>>
>

I apologize for the confusion here. I don't know what I was thinking. Maybe I shouldn't post after pulling an all-nighter.

> Sorry, I don't see what words like subsuming or conflating have to do with
> this unless they are what you are trying to embody for mystical reasons.
> If you want to see a more complicated mental construction just because you
> think "it's really there in actuality", I can't stop you but it hardly
> seems necessary.

>

>

>