Re: Example of expression bias?
Date: 20 Jun 2006 17:04:58 -0700
Message-ID: <1150848298.862654.212300_at_u72g2000cwu.googlegroups.com>
Well, here we are again ...
Cimode wrote:
No I'm not. You're about to try though. I would also point you towards
a boxed out section, in bold type, two-thirds of the way down page 114
in the 7th edition of Date's Introduction to Database Systems. The
preceding paragraph is also helpful.
> A relvar has associated properties among which
> You are redefining RM.
> a data type expressing how it draws values from a domain and restricts
> that extraction only to permissible values.
>
> A data type in RM = (a domain1 to draw values from) + (restrictions
> implemented on domain1 --> domain constraint) + (operators that can be
> defined using that data type)
>
> An attribute does not belong to a data type. A data type is the set of
> rules that apply to attribute for saying whether or not values in
> tuples are permissible values in the system.
>
> That's what I mean by saying you are at implementation level.
>
That's another plus for FP; if you manage to define an acceptable set
of denotational semantics, it doesn't take a lot of work to turn them
into an executable specification. Maybe that's why Perl 6 is (according
to Larry Wall, anyway) being trial implemented in Haskell. Off topic,
but mildly interesting in context.
> If you are considering that data types are not defined in RM. That
And if you're thinking that what RM has to say about data types
constitutes a complete, sound and usable definition of data types,
> shows the level of ignorance about RM concepts your in.
>
> If you state that RM has said nothing about data types: It can only
> mean one thing -->you have never read a book about RM.
>
I've read a few; they've had little to say about data types, apart from they exist, you need them, and you need to be able to define your own. (Date moves on into how to define your own via Tutorial D; but since the starting point is that types are orthogonal to the relational model, this is "add-on" territory, not fundamental to RM itself.)
> I am tired with you.
>
> I have asked a question you did not answer.
>
> Definition RM, through SQL perception limits the understanding of RM.
>
> That FP is a set of definition sufficiently clear. All I have seen so
> far in your definition is fuziness..
>
> No. If the answers were convincing, I may have paid a closer look.
> But I confirm what I thought.
Now there's a surprise. Received on Wed Jun 21 2006 - 02:04:58 CEST