Re: 3vl 2vl and NULL

Frank Hamersley wrote:
> dawn wrote:
> > Frank Hamersley wrote:
> >
> [....]
> >
> > If the data model visualized on the screen has one instance of an ID
> > and the SQL view backing that screen has many instances of this same ID
> > value, then the data models are different.
>
> Are we talking about the model or manifestations of it (instances)?

We are talking about the logical model itself, but perhaps using that term differently. A logical model that is in first normal form is different from a model of that same data that is not. They are not the same model simply because they model the same thing. Trees, networks, and relations might all model the same data, but they are not the same model. The model associated with a screen of data is not typically a no-repeating-groups relation as required if it were to be output directly from a SQL-92 view.

>
> [..]
>
> >>I think you have expressed most clearly the core of the problem
> >>troubling you. It seems you can't accommodate the SQL outcomes because
> >>it doesn't have a "shape" that you are comfortable with.
> >
> > I'm actually quite comfortable with it, but I don't see an advantage to
> > using it to the extreme typically employed with SQL-DBMS's.
>
> I'm missing something - what is the "extreme" bit?

If there really is a reason to have data in base relations with no repeating groups, surely that requirement goes away with relations that are logical views of the data. SQL permits views not to be in 2NF, 3NF, BCNF, 4NF, ... but took this notion of no repeating groups to the extreme and requires it even in logical views of the data.

> >>That is
> >>something for you to deal with although I suspect you are not alone.
> >>The vast number of cursor happy application developers are a testament
> >>to that.
> >
> > I like set manipulations, but have no need to block other types of
> > access where useful.
>
> So do I, and I rarely find other types of access useful. Admittedly
> there are some and I will freely confess to the occasional use of a
> cursor as a last resort.
>
> >>Good luck on the journey Grasshopper!
> >
> > Much appreciated Master.
>
> Thats a good first step :-)

I've worked with men my entire career.

> >> BTW may good fortune also attend the blog.
> >
> > Thanks, Frank. I don't know how many cdt readers will take the journey
> > with me as there are a lot of relational disciples here who might have
> > had enough of me. I will only announce the first entry here. I am
> > working hard to ensure it is accurate, easy to tell when I am stating
> > facts compared to opinions, bold, and a good read. It will come out
> > next week. Cheers! --dawn
>
> Personally I'm a bit over blogging per se, but will take a look at least
> when you inaugurate.

I didn't want to call it a blog since it sounds like a personal log, but that is pretty much what columns of articles posted to the web are called these days. So without going for therapy, I've decided I'm able to call it a blog which would make me, ugh, a blogger. (Still hard to say, heavy sigh) It just means I will give more thought to the structure of my writing than I do in this forum. Cheers! --dawn

>
> Cheers Frank.
Received on Sat Jan 07 2006 - 14:02:42 CET