Re: [xml-dev] XML Schema as a data modeling tool

[Damian Morris <damian@moso.com.au>]

First of all, +1 for everything Michael has said on this subject. (Although, you can usually take that as a given.)

Perhaps another way of looking at what Michael is saying is that it is the difference between "X contains a Y" and "X has a Y" - for example, an Address can be considered to "contain" a Street - the Street is intrinsic to the Address; however, a Person "has" an Address - there is a relationship there, but the former does not contain the latter in any meaningful sense.

Hierarchical models better suit "contains" relationships, but the real world is full of "has" relationships, which are more naturally described by network models.

Cheers,

Damian

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On 01/10/2013, at 5:32 PM, Michael Kay <mike@saxonica.com> wrote:

> Data modelling for me is all about achieving a shared understanding of =
> the problem. It's something I usually do interactively on a whiteboard. =
> The resulting model needs to fit on the whiteboard and it needs to be =
> thrown away when you've finished - if it wasn't simple enough to be =
> memorised, then you have failed.
> 
> For example I once did a workshop with people from a broadcaster. It was =
> all about programme scheduling. It was primarily about getting to a =
> point where everyone in the room had a common understanding of what they =
> meant by words like "programme", "advertisement", "channel", etc -- =
> which all led to some very interesting debates; and of course you =
> sometimes agree to split the concept, so =
> what-engineers-mean-by-a-channel becomes a different concept from =
> what-marketeers-mean-by-a-channel.
> 
> The whiteboard ends up with lots of boxes and arrows because ultimately =
> the way to define a concept is to show how it relates to other concepts: =
> an-ad-is-a-kind-of-programme, a-program-has-many-transmissions, =
> a-transmission-happens-on-a-channel.
> 
> I simply can't imagine doing this kind of exercise and restricting the =
> stuff on the whiteboard to be a hierarchy. It would be like restricting =
> yourself to only use one colour of felt pen: why would anyone want to do =
> that?
> 
> Yes, there's a sense in which the term "real world" is unfortunate; the =
> model is always synthetic, and abstraction is vital. But I find the term =
> useful, because it reminds people that we are trying to improve our =
> understanding of the way things "out there" behave, not to design data =
> structures that are convenient to implement.
> 
> Michael Kay
> Saxonica
> 
> 
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