RE: [xml-dev] RNG vs. XSD : is the use of abstract types andpolymorphis

["Costello, Roger L." <costello@mitre.org>]

John Cowan wrote:

> See http://www.thaiopensource.com/relaxng/design.html#section:15 
> for James's thinking on inheritance in schema languages.

Fascinating!

Here are a few excepts from the article:

    One of the most significant differences between RELAX NG and 
    W3C XML Schema is that RELAX NG does not have any concept 
    of inheritance. 

    Inheritance has proven to be very useful in modeling languages 
    such as UML. However, I would argue that trying to make an XML 
    schema language also be a modeling language is not a good idea. 
    An XML schema language has to be concerned with syntactic details, 
    such as whether to use elements or attributes, which are irrelevant 
    to the conceptual model.

    ... there is no need for it to support inheritance; the role of the schema 
    language is purely to describe the XML syntax used to represent the 
    conceptual model.

    ... the role of the schema language is purely to describe the XML syntax 
    used to represent the conceptual model. RELAX NG has the advantage in 
    this role that it provides more flexibility in the choice of syntax.

/Roger