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

[Michael Kay <mike@saxonica.com>]

Well, let me start by pointing out the drawbacks, seen very severely on a project I did some consultancy for, where they had indeed used XML Schema for a large scale enterprise data model:

(A) XSD isn't very good at modelling relationships. It's a hierarchic model, whereas the real world is a network. Modelling relationships other than aggregations therefore involves some arbitrary decisions on representation, which you don't really want in a conceptual data model.

(B) XSD is designed for representing messages rather than for creating an enterprise data model, and it's very easy to get the two confused. It might be that every employee has a salary history, but that doesn't mean the salary history has to be part of every message concerning the employee. The relationship between the conceptual reference model and the design of individual messages can be quite indirect. There are really several separate problems here: (a) XSD was designed for message/document design, not for conceptual modelling, (b) designing a family of schemas for a large set of message types, with reuse of components across all the message types, is itself rather difficult and there's very little in XSD that makes it easier, (c) message design has to take the process model into account, not just the data model.

Michael Kay

Saxonica

On 30 Sep 2013, at 09:27, Hans-Juergen Rennau wrote:

Hello everybody,

I am interested in approaches to use XML Schema as a technology for constructing data models, which have a scope exceeding the definition of exchange messages (e.g. web service design). One idea may be to use XML Schema for the construction of a "reference model" to which message structures can be related, and I think this is a basic goal of NIEM. Another idea may be to use XML Schema for creating a conceptual data model to which relational database schemas may be related, offering unambiguous points of reference to which semantics and metadata may be connected. So I wonder, is XML Schema also used for enterprise-scale data modelling?

Much promise seems to be implied by the fact that XML Schema describes tree structures, is firmly based on an elaborate information model (Infoset/XDM) and is clearly related to URIs - which makes it a candidate resource for generating various other resources from it with immaculate reliability.

So I would like to learn about approaches of using XML Schema for data modeling purposes - goals, benefits, limitations, case studies, etc. etc. If anybody has any links, information or thoughts, it would be appreciated.

Thank you very much,

Hans-Juergen