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

Date: Sun, 13 Jun 2004 23:20:13 +0200

Message-ID: <40ccc506$0$48920$e4fe514c_at_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.*

>>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 - 23:20:13 CEST