Re: foundations of relational theory? - some references for the truly starving

"Mike Preece" <michael_at_preece.net> wrote in message news:1b0b566c.0310240556.3bf271e6_at_posting.google.com...
> >
> > BS. Or do you mean you don't write to log files ?
>
> No - we don't usually. It's not usually wanted or needed. We can if
> you want. It's very easily done - centrally, with a trigger fired when
> the file is updated if you'd like.

So, what happens if you have a power failure or an OS or application crash when you've written the first page of a two-page update? Does Pick have transactions?

> Ah - now there's something interesting! I often see people use "then"
> when I think they mean "than". Is this an american thing or what?

I suspect Costin is not a native speaker of English. While he is, in fact, jaw-droppingly educated as near as I can tell, his diction is idiomatic in a way that sounds distinctly non-native to me, an American.

> Databases exist to record and retrieve data.

I've always felt that this is what filesystems are for. Database management systems are for quite a number of more interesting and useful things, (in addition to being useful for data persistence.)

In fact, I can imagine situations where I *wouldn't* need persistence but I would want a DBMS. If I was crunching up a bunch of numbers and was happy to restart upon a crash, say.

> And 'normalisation'? You have to fit your data into a 2 dimensional
> structure although you get the sneaking suspicion sometimes that it's
> actually a lot more difficult to do so than it should be somehow?

Well, it never seems that difficult to me, but I've been taught how to do it.

BTW, normalization is the process of removing redundancy from a schema. A fully-normalized schema is said to have no redundancy, not be fully two dimensional.

Actually, calling relations "two dimensional" is a common misconception. Relations are not two dimensional; they are n dimensional, where n is the number of attributes. You can print out points in an n-dimensional space on a piece of paper by listing the value in each of the n dimensions one after the other, one per line; that doesn't make the data two dimensional.

Here's some different examples of colors from the three dimensional eight bit RGB color space:

R G B

127 127  127  // gray
0 255 255      // cyan
0 255 0        // green

Is this data three-dimensional or two dimensional? Answer: the data is three dimensional, but the presentation of the data is two dimensional if you view it on a monitor. If you view it on a punch tape, the presentation would
be one-dimensional.)

Marshall Received on Sat Oct 25 2003 - 06:38:23 CEST