Re: Few confusing things about first normal form
Date: Sat, 1 Nov 2008 05:28:55 -0700 (PDT)
On Oct 26, 6:47 pm, JOG <j..._at_cs.nott.ac.uk> wrote:
> On Oct 24, 3:27 am, David BL <davi..._at_iinet.net.au> wrote:
> > On Oct 23, 9:11 pm, paul c <toledobythe..._at_oohay.ac> wrote:
> > > David BL wrote:
> > > ...
> > > > Is the value of an attribute that is an RVA a scalar?
> > > I believe it is ie., in a "containing" tuple it's a (single) relation
> > > value and (in the D&D approach) there is no way to operate on its
> > > individual tuples. Their algebra only operates on the value of the
> > > relation.
> > > (They have an operator called UNGROUP that forms a different relation
> > > that has no RVA's. Definition in thethirdmanifesto.com, see appendix A.
> > > They don't the equality operator to treat the second relation as equal
> > > to the first even though some of the possible values for the containing
> > > /GROUPed relation might have exactly the same information as the
> > > UNGROUPed one. However, I don't believe they forbid an operator apart
> > > from equality that decides some kind of equivalence.)
> > > Hope somebody will correct me if I've mangled what D&D say.
> > Isn't every type a scalar type? Why not drop the word "scalar" as
> > meaningless? In fact it would seem a good idea to avoid the
> > confusion with the rather specific meaning of "scalar" used in linear
> > algebra (where it is associated with the field over which matrices and
> > vectors are defined).
> There is clash between the compsci use of the term, and the
> mathematical use. AFAIK Codd meant the former, a scalar meaning a
> variable that can only hold one value meeting the variable's type. One
> logical address - one item. This contrasts with an array, for example,
> which can contain more than one value, but does not require any form
> of decomposition to iterate through those values (i.e. it is not an
> object). One logical address - several items (lined up contiguosly)
> While this once made sense in the low-level programming world, the
> uptake of OO (and specifically templates and containers) has severely
> confused these distinctions - an "Array" in pure OO languages /does/
> require decomposition (through accessor methods), it is just that this
> is often hidden via overloading of an indexing syntax to mimic non-
> scalars (i.e. square brackets). A <vector> for example is one item, at
> one logical address, that just happens to contain lots of others.
> Hence, to a modern high level programmer, who probably wouldn't have
> any notion of contiguous memory addressing, all variables are scalars
> and for it to be otherwise would seem bizarre.
this is a big "depends". the need for contiguous memory addressing varies from not needed (a business tracking customers is easily relational), to pretty much mandatory (signal processing/ multimedia, do you really need to put each video frame into an oracle table record so that the customer can view your movies over odbc?). It is probably more of a definition of what you want your computer to be doing as a programmer. Received on Sat Nov 01 2008 - 13:28:55 CET