Home -> Usenet -> comp.databases.theory -> Re: Codd provided appropriate mathematics ... (was Re: Relational and MV (response to "foundations of relational theory"))

Re: Codd provided appropriate mathematics ... (was Re: Relational and MV (response to "foundations of relational theory"))

From: Dawn M. Wolthuis <dwolt_at_tincat-group.com>
Date: Fri, 27 Feb 2004 15:20:33 -0600
Message-ID: <c1ocbm$ldq$1_at_news.netins.net> 












Your last statement, Eric, is really the 
point.  I think the original idea was that relational database theory was 
tied to mathematical relations.  It is now at the point where statements 
that are true of mathematical relations such as the fact that relations are 
ordered, are now considered "obviously" untrue in the database relational 
model.  Ah well, such is the nature of language.  --dawn



  
"Eric Kaun" <ekaun_at_yahoo.com> 
  wrote in message news:L9O%b.18045$HM4.16491_at_newssvr31.news.prodigy.com...

  
Do you mean relational as in mathematics? The 
  relational model for data is a specific application of mathematical relations. 
  Are those examples you give below really relational in the sense of the 
  relational data model? I doubt it. They might have something to do with 
  mathematic relations, but that's a different thing entirely.

  

    
    
This is just plain false.  There have been 
    many relational models proposed that are not 1NF.  See for example, 
    ABITEBOUL, S.; BIDOIT, N. Non first normal form relations to represent 
    hierarchically organized data. In: PODS, 1984. Proceedings. . .Note the 
    date: 1984.  This is supposed to be a database theory board but it 
    seems more religious than theoretical!

    
 

    
"Alfredo Novoa" <alfredo_at_ncs.es> wrote in 
    message news:403f7915.12870647_at_news.wanadoo.es...
> On Fri, 27 
    Feb 2004 08:01:43 -0600, "Dawn M. Wolthuis"
> <dwolt_at_tincat-group.com> 
    wrote:
> 
> >> The Relational Model permits relation typed 
    attributes, so
> >> "multivalued" does not have any advantage. 
    Collection typed attributes
> >> don't violate 1NF.
> 
    >
> >Yes, so the theory in RDM is evolving to the point where it 
    might become
> >more practical in its application.
> 
> 
    The understanding of The Relational Model is better now than in the
> 
    70's, but the model is always the same. 
> 
> But relation typed 
    values in base relations seem to have little
> utility. The only good 
    practical use I have found to the moment is to
> use them to implement 
    a candidate keys relation variable of a catalog.
> 
> > But 
    while each RDBMS vendor seems to
> >have a means now of storing an 
    array (or relation or other collections),
> >querying against this 
    data is done differently by each vendor, it seems,
> >although 
    SQL-99 has a means of doing this (and perhaps more db vendors are
> 
    >employing that standard, but when I checked in 2002 there was no
> 
    >consistency).
> 
> As you heared hundreds of times, SQL is 
    not relational. You will not
> find the term relational in the SQL 
    specifications.
> 
> >> Relations are in 1NF by 
    definition. With a RDBMS you can not violate
> >> 1NF even if 
    you want.
> >
> >You can violate any of the other normal 
    forms, but not 1NF.
> 
> Because you have no way. Relations are 
    in 1NF by definition, otherwise
> they are not relations. If a DBMS 
    does not use relations then it is
> not a RDBMS, so if you can violate 
    1NF then you are not using a RDBMS.
> A simple tautology.
> 
    
>  
> Regards
>   Alfredo 


Received on Fri Feb 27 2004 - 22:20:33 CET












Original text of this message