Mm. I said, approximately: "Hierarchy is essential, and to give it the right place in our modelling we must determine the right boundaries, the right granularity."
Then you wrote:
"Within these real-world entities like books and authors there is
hierarchic attribute information (such as the brands or imprints
belonging to the publisher, or the branches of the retailer) and
normalizing these all only complicates the model. But any attempt to put
books under authors or authors under books is essentially misguided."
So while it is clear that we agree about this - one may choose the wrong boundaries, coercing parts into a single hierarchy which is not durable - it is not quite clear whether you attach much importance to hierarchy even if designed properly.
But no - it is clear: saying "the hierarchies we play with are usually arbitrary projections of a network", you leave no doubt that we cannot get far beyond boxes and lines, in your view. No forests, in your view.
Thank you for the clarification.
Hans-Juergen
Von: Michael Kay <mike@saxonica.com>
An: Hans-Juergen Rennau <hrennau@yahoo.de>
CC: "xml-dev@lists.xml.org" <xml-dev@lists.xml.org>
Gesendet: 23:24 Montag, 30.September 2013
Betreff: Re: [xml-dev] XML Schema as a data modeling tool
On 30 Sep 2013, at 21:49, Hans-Juergen Rennau wrote:
> Michael, you sound as if hierarchy is mainly the result of applying this or that view to a network, the mere results of transformations, without substance of its own. I disagree.
>
Yes, I think the hierarchies we play with are usually arbitrary projections of a network. They work well for documents or messages, they don't work well for
models of things in the world. If you take any real-world domain - something like books, authors, publishers, and retailers, there's no natural hierarchy between them. You can force a hierarchy if the technology constrains you to do so, but it's artificial - and conceptual data models shouldn't be constrained by the technology you are using.
I'm NOT saying that a conceptual data model should be in 3rd normal form. Within these real-world entities like books and authors there is hierarchic attribute information (such as the brands or imprints belonging to the publisher, or the branches of the retailer) and normalizing these all only complicates the model. But any attempt to put books under authors or authors under books is essentially misguided.
Michael Kay
Saxonica
