Re: XML Schemas: Best Practices

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

Curt Arnold wrote:
> 
> Another limitation or concept (depending on your point of view) of
> substitution groups is that an element can only participate in one
> substitution group.

I am not sure that I understand all the implications of this.  

Let's take the Catalogue example.  We created two elements, Book and 
Magazine, and put them in the substitutionGroup with the abstract 
element Publication:

    <element name="Book" substitutionGroup="c:Publication" 
             type="c:BookType"/>
    <element name="Magazine" substitutionGroup="c:Publication" 
             type="c:MagazineType"/>

Thus, anywhere <Publication> may occur, it may be substituted by
<Book> or <Magazine> (in fact, it must be substituted by one of these
elements since it is abstract).

<Book> and <Magazine> may "only" substitute for <Publication> and no
other element, since they may be in only one substitutionGroup. And,
this is limiting.  Is that what you are saying?  Anything else?
/Roger