Re: In an RDBMS, what does "Data" mean?

From: mAsterdam <mAsterdam_at_vrijdag.org>
Date: Sun, 13 Jun 2004 23:20:13 +0200
Message-ID: <40ccc506$0$48920$e4fe514c@news.xs4all.nl>

Dawn M. Wolthuis wrote:
> mAsterdam wrote:

>>Dawn M. Wolthuis wrote:
>>"x" wrote:
>>>>>So if I put my data into an MV database I can access
>>>>>it as if it were in
>>>>>an RDBMS. However, the converse is not true.
>>>>
>>>>So all data in a MV database can be represented in relational model,
>>>>but not all data in a RDBMS can be represented in MV model :-)
>>>>
>>>>Which one is more expressive ? :-)
>>>
>>>Easy question -- 
>>>
>>>if each model can provide a solution for a particular 
>>>area so that we have
>>>both an MV and a SQL-DBMS solution and
>>>
>>>if we can look at the MV model as relational
>>>when we choose to do so (which
>>>is usually for the purpose of using SQL against it)
>>>but we cannot take the relational model and view
>>>the MV model from it
>>>
>>>Then clearly the more expressive language is ... 
>>>NOT the one that loses the
>>>ability to view the data in some other way, right?  --dawn
>>
>>So now we have language R and language M.

>
> A business problem is brought to people who encode a solution in R and in M.
> They make the usual design tradeoffs based on whichever implementation they
> are doing. The M solution can toggle to show you an R view
> of the solution,

... and have the R view show *all* data present in the M solution ...

Ergo language R is capable of expressing all possible M expressions.

> but the R solution does not have the ability to show an alternate
> solution, but the R solution does not have the ability to show an alternate
> M view of the solution.

Ergo language M is not capable of expressing all possible R expressions. It does not matter which product does the translation.

> Now, you could design an R solution that does
> permit you to view it as this M solution, but you would have to have decided
> in advance to do that, otherwise it is likely you will make design decisions
> that rule out getting back to the original M solution.
>

>>R 'loses the ability to view the data' from within M and that
>>would somehow mean M is *more* expressive?
>>The only way I could make sense out of that is
>>if the (appearant) excess expressions in R could
>>*not* be relevant to a solution.
>>
>>Do you have an indication as to what those excess expressions are?

>
> they tend to be data that were collected and stored in the M solution and
> designed out (deemed unimportant to retain) for the R solution.

Just to get it straight: These 'designed out' data *can* be represented in R (inferred from the R translation of the M solution), but they are *not* represented in R because of the different design process (ispired by the nature of M cq. R)?

>>Which statements can you make in R but not in M - IOW
>>of which data does R lose 'the abitlity to view the
>>data in some other way'?

>
> It is not what cannot be done, but what will not be
> done with R that is the problem.
>

>>x's question may be easy, your answer sure isn't.

>
> Sorry 'bout that. --dawn

It seems to me this is a doubly edged sword.

The product using the M language is capable of showing all of its data in the R language. The R products are not capable of showing all data in the M language.

Factor out the products, and you get:
Language R is capable of expressing all possible M expressions. Language M is not capable of expressing all possible R expressions.

It is still interesting to see what kind of expressions fail to translate. Received on Sun Jun 13 2004 - 16:20:13 CDT