Re: XML Schema as a data modeling tool

Thank you, Michael. You wrote "It [XSD] is a hierarchic model, whereas the real world is a network." I would say, it is as much a network as it is hierarchic. Think of economic structures (e.g. a shop inventory), of administrative structures (a registration procedure), of biological structures (a cell). At any rate the structures I have been dealing with were usually hierarchic, unwieldy and confusing if not dealt with as such, and often straightforward to handle, otherwise. I could show you an ER diagram representing over 100 relational tables storing shopping cart data, and also a single tree representation which can be read like a newspaper. A concise tree representation can be read like a text, conveying a sense of the whole. An ER diagram with many boxes and very many lines is very hard to read. Doubtless you are right in warning about the problems how to model relationships which do not correspond to containment. But I wonder - would you really suggest giving up the benefits of hierarchical modelling, and what is the alternative? You know the German saying, "Not to see the wood because of all those trees", which I suggest to invert, not to see the trees, because they are part of a wood.