Andrew Welch writes:

> With global definitions some documents will be valid that you might
> not want, for example an XML document of just <header/> would validate
> using that schema.

That's a bit of an oversimplification.  The schema recommendation says the =

following about the ways in which a schema may be used to validate an 
instance document [1]:

-------------
With a schema which satisfies the conditions expressed in Errors in Schema =

Construction and Structure (=A75.1) above, the schema-validity of an elemen=
t 
information item can be assessed. Three primary approaches to this are 
possible: 
1 The user or application identifies a complex type definition from among 
the {type definitions} of the schema, and appeals to Schema-Validity 
Assessment (Element) (=A73.3.4) (clause 1.2);
2 The user or application identifies a element declaration from among the 
{element declarations} of the schema, checks that its {name} and {target 
namespace} match the [local name] and [namespace name] of the item, and 
appeals to Schema-Validity Assessment (Element) (=A73.3.4) (clause 1.1);
3 The processor starts from Schema-Validity Assessment (Element) (=A73.3.4)=
 
with no stipulated declaration or definition, and either =B7strict=B7 or =
=B7lax=B7 
assessment ensues, depending on whether or not the element information and =

the schema determine either an element declaration (by name) or a type 
definition (via xsi:type) or not.
-------------

If you choose to use a processor that implements the third option, then 
your statement is correct.  If you want to ensure that the root element is =

"component", then you should get a processor that implements option #2, 
and designate the declaration for element "component" as the one from 
which validation is to start.

By the way, among the reasons that option 3 is provided, is to facilitate 
the creation of incremental validators.  Let's say you have an editor 
that's helping you enter these documents.  Even though you want the 
document as a whole to be rooted at <part>, it's possible that you are 
editing a "header".  Rule 3 allows such an editor to revalidated just the 
<header> element as it is changed, even though it is not the root of the 
document.

Noah

[1] http://www.w3.org/TR/2004/PER-xmlschema-1-20040318/#validation=5Foutcome

--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------





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