Re: Database-valued attributes?

First, how do you type a database value? For any change in the schema of the database, do you have to redefine the type?

Second, why not just encapsulate the type and not expose the representation of the database value as either columns or tuples? Nice and simple. Just make sure you define a pretty good default representation.

Dan

"Paul Vernon" <paul.vernon_at_ukk.ibmm.comm> wrote in message news:boqhlv$1226$1_at_gazette.almaden.ibm.com...
> "Jonathan Leffler" <jleffler_at_earthlink.net> wrote in message
> news:Ir%rb.7052$nz.2397_at_newsread2.news.pas.earthlink.net...
> > Marshall Spight wrote:
> >
> > > There's been the occasional incidental discussion of relation-valued
> > > attributes on the list lately. This has got me thinking: what about
> > > database-valued attributes? That is to say, what about an attribute
> > > that consists of a set of relation values?
> >
> > Hmmm...would the elements of the set of tables all need the same type?
> > In the RMD (relational model of data), the values in a column are
> > homogeneous in type, usually. For example, in a table with one or
> > more RVAs, the RVAs for a given attribute have the same structure/type
> > in each row.
> >
> > What is a database? That isn't intended to be wholly facetious.
>
> No, indeed this is a very important question, and not one that to my
> knowledge that has an agreed answer. Well, I have an answer, but I don't
> believe that is it is widely agreed upon.
>
> See this thread
> http://groups.google.co.uk/groups?selm=3cccff99%241%40news.uia.ac.be
>
> In particular, Jan's comments:
> "a database instance is not a set of relations but more like a tuple of
> relations"
>
> "I have seen lots of formal definitions of a relational database and not
one
> of them defined a schema as a set (as in set theory) of tables (or
> relations, to be more exact)."
>
>
> Oh, my answer is that
>
> a database is a set of tuples.
>
> nice and simple.
>
> :-)
>
> P.S. That's tuples not necessarily of the same type of course.
>
>
> Regards
> Paul Vernon
> Business Intelligence, IBM Global Services
>
>
Received on Wed Nov 12 2003 - 07:23:33 CET