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Re: Basic XMLSchema questions

• From: Brett McLaughlin <bmclaugh@a...>
• To: Alan Santos <asantos@o...>
• Date: Wed, 05 Jan 2000 15:13:37 -0600

Alan Santos wrote:
> 
> Thanks for the quick response Brett.
> 
> In the example below, I understand the point of <datatype>,
> but what is <type> getting us?  Don't you have the same thing without it?

Nope.  This:

> > <element name="myElement">
> >     <element name="nestedElement" type="string" />
> >     <element name="anotherNestedElement" type="string" />
> >     <attribute name="isPrimary">
> >       <datatype content="empty" />
> >     </attribute>
> >     <attribute name="focus">
> >       <datatype content="NMTOKENS">
> >         <enumeration value="Java" />
> >         <enumeration value="C" />
> >         <enumeration value="XML" />
> >       </datatype>
> >     </attribute>
> > </element>

is mucho illegal.  Remember that XML Schema will be handled by SAX,
which is sequential.  So SAX must know _ahead_ of time that it is going
to be dealing with a compound type.  That way it can know to allow
multiple element definitions within another definition.  

Without the <type> construct, SAX would have to "magically" know when
nested element definitions are legal and when they are not... I know
there are other good reasons, too, although I'm too tired to think of
them... sorry.. ;-)

-Brett

> 
> > for example:
> >
> > <element name="myElement">
> >   <type>
> >     <element name="nestedElement" type="string" />
> >     <element name="anotherNestedElement" type="string" />
> >     <attribute name="isPrimary">
> >       <datatype content="empty" />
> >     </attribute>
> >     <attribute name="focus">
> >       <datatype content="NMTOKENS">
> >         <enumeration value="Java" />
> >         <enumeration value="C" />
> >         <enumeration value="XML" />
> >       </datatype>
> >     </attribute>
> >   </type>
> > </element>
> >
> 
> > Your schema is one-to-one with a Java class?  This wouldn't be a good
> > idea, unless I'm misunderstanding your intent.  Maybe your _XML_ is
> > based on a class, and it specifies the class, but then multiple XML docs
> > (therefore multiple classes) all use the same Schema.
> >
> 
> The _XML_ contains instances.  But felt it was more appropriate within the
> schema document.  (Or some other xml instance document)
> 
> Why do you feel it is a poor decision?
> Am I abusing the intent of  an XML Schema in a horrible manner?
> Perhaps XMI is a better option for my needs?
> 
> > Why not?  What's the difference in your mind?  If you can define an
> > infinite number of types, and define an infinite number of elements with
> > any defined type, how is that not flexible?
> 
> Sorry, it is flexible, it just means more work for me, and users of my
> application.
> 
> Now we need two elements  when we wish to add a new type to the schema
> (unless I'm missing something else)
> 
> (e.g. <element name="xxxReference"/>
> <element name="xxx"/>)
> 
> thanks,
> alan

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