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Re: Pizza Example

From: Anthony W. Youngman <wol_at_thewolery.demon.co.uk>
Date: Thu, 22 Apr 2004 00:14:48 +0100
Message-ID: <Y7ZBlTBoBwhAFwS2@thewolery.demon.co.uk>


In message <bQ9hc.10110$R66.4848_at_newssvr31.news.prodigy.com>, Eric Kaun <ekaun_at_yahoo.com> writes
>"Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message
>news:0IV6pcCYeDhAFwEv_at_thewolery.demon.co.uk...
>> In message <2HQgc.9747$gG5.9105_at_newssvr31.news.prodigy.com>, Eric Kaun
>> <ekaun_at_yahoo.com> writes
>> >"Anthony W. Youngman" <wol_at_thewolery.demon.co.uk> wrote in message
>> >news:ym$bCWJIqvfAFw3f_at_thewolery.demon.co.uk...
>> >Good question; in this case I meant simple as advocated by Occam's Razor.
>> >Fewer concepts, and more consistent notation.
>>
>> Occam's razor - as phrased by ?Einstein - "Things should be as simple as
>> possible - but no simpler".
>
>Agreed.
>
>> To me, relational has simplified too far - "The car is blue and green",
>> "John is Mike's dad". If I model both these situations in relational, I
>> need a relation to link the colours to the car. I need a relation to
>> link John and Mike. In the first situation I'm linking an entity with
>> its attributes. In the second I'm linking two entities. Relational makes
>> no distinction between the two types of link ...
>
>Does it have to? Remember, we're modeling data, not "the real world" (unless
>you want to build a small model of a car and paint it blue and green, which
>is up to you). It's not a model in the same sense as you discuss elsewhere
>with physical models.

But the data is representing the real world -if it doesn't, what's the point of it?
>
>Unless, of course, you claim to have seen DATA in the "real world" with your
>own eyes. I don't mean Brent Spiner in Star Trek: The Next Generation.
>
>And in any event, the case you cite is very simple (colors, which are in
>most models scalars, make the argument for 1NF less persuasive than in other
>cases). Other cases like children, line items, and any business data I can
>think of are another matter. The line between entity and relationship, while
>there, is fuzzy. Basing your statements of fact on normalized predicates is
>much less ambiguous, and this clarity of design guidance is another benefit
>of relational. There will always be an appeal to the business domain you're
>modeling, but given that, normalization rules are much better guides than
>anything else I've seen.
>
>> >Define "complex." It usually depends on the "object" - oh, can you define
>> >that as well?
>>
>> Well, I'd define a real world object as something described by a noun -
>> an invoice, a car, a person ...
>
>Attributes are nouns.

I thought they were adjectives. For example, "the car is blue" - "blue" is an adjective.
>
>I'm not just being argumentative. I think it's a credit to relational that
>it (tries to) base itself on predicates, as opposed to entities,
>relationships, and attributes, is stronger for many reasons covered in books
>already mentioned...
>
>> > "the data" is
>> >what the entire disagreement is about. Is it a set of attribute values?
>Is
>> >it an object graph? Is it both, meaning we've decided in advance the view
>of
>> >"the object" everyone must have because it's "real world" (can you define
>> >that?).
>>
>> Typically, it's a set of attribute values. And yes, I see what you mean
>> - given the primary key, a relational view will return (after a lot of
>> work if it's scattered across many tables) all the attributes associated
>> with an entity. With Pick, it is a single "row" in a single "table".
>
>And the decision of what "it" you're talking about is likely to be premature
>and limited in usefulness. The up-front simplicity of modeling based on
>entities is undercut by its application focus.

In practice, it actually seems to work extremely well...
>
>> Well, yes, the fact that in relational N is only ever 2 makes life
>> simple.
>
>HA! So you admit it? :-)
>
>> But that's a "cosmological constant" which upsets purist
>> physicists. If I can solve a problem for N where N is any number, it's a
>> far better solution than if it only works for "N=2" :-) (and actually,
>> both the values you've quoted for N I've met in practice :-)
>
>Uh... I suspect there's another model / meta-model confusion here, but the
>margin of this message is too narrow to contain the marvelous proof I've
>concocted.
>
>- erk
>

Cheers,
Wol

-- 
Anthony W. Youngman - wol at thewolery dot demon dot co dot uk
HEX wondered how much he should tell the Wizards. He felt it would not be a
good idea to burden them with too much input. Hex always thought of his reports
as Lies-to-People.
The Science of Discworld : (c) Terry Pratchett 1999
Received on Wed Apr 21 2004 - 18:14:48 CDT

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