Re: Schema validation using multiple schemas

[Adachi Seiichi]

Thanks for the explanation on the schema processors.  I now understand
better on how they are implemented and how they work.  Is the general
principle Jeff stated specified in some specification?

I also understand that the only path to successful validation across
implementations may be to specify a schemaLocation for each namespace in
the XML instance.
But for a person creating the XML instance, they may not know how the
schema processor is implemented.  Is it specified somewhere on the
policy concerning how to use <xsi:schemaLocation> and <xsd:import> in
these cases?  (Maybe like in a w3c document that it is recommended all
namespaces used in the XML instance should be specified in the
<xsi:schemaLocation> element or something similar?)
For example for the <include> element which is clearly stated (in "XML
Schema Part 0: Primer Chapter 4.1 A Schema in Multiple Documents") that
when there are multiple schema documents and only the 'topmost' document
is referenced, the processor must gather all the definitions from all
the included documents.  (Which would of course mean that only the
'topmost' document needs to be specified)

Thanks,

Seiichi


>From: "Bob Foster" <[EMAIL PROTECTED]>
>Reply-To: [EMAIL PROTECTED]
>To: <[EMAIL PROTECTED]>
>Subject: Re: Schema validation using multiple schemas
>Date: Tue, 26 Aug 2003 18:10:53 -0500
>
>Yes, that all makes sense. I still believe, in addition, that the ability 
to
>locate a schema for a namespace based on an import in another schema is
>implementation-dependent. A processor is not required to do anything with
>the schemaLocation in an import, including remember it.
>
>On the other hand, an implementation _could_ work by first fetching all
>schemas applicable to a node, then using the information from these 
schemas
>to locate a schema for the namespace of the root node. This would make the
>original example work, but it would again be implementation-dependent.
>
>In another circumstance, one might be expecting lax validation based on a
>schema locatable only through an import in another schema, but if the
>processor is unable to locate the schema in this way it will quietly 
accept
>anything from the namespace. You think you have validation, but you don't.
>
>I think the following is true: The only guaranteed path to successful
>validation across implementations is to specify a schemaLocation for each
>namespace in the document you expect to be subject to strict or lax
>validation.
>
>Bob
>
>----- Original Message -----
>From: "Jeff Greif" <[EMAIL PROTECTED]>
>To: <[EMAIL PROTECTED]>
>Sent: Tuesday, August 26, 2003 11:18 AM
>Subject: Re: Schema validation using multiple schemas
>
>
> > Here are the general principles:
> >  1.  The schema processor must be able to obtain the location of all
>schemas
> > it must use to validate the instance document and the schemas used to
> > validate that document (if this level of validation is desired.)
> >   2.  **While reading a schema** it can use that schema's imports to 
find
> > schemas on which the first schemas depend, and so on recursively.
> >   3.  It must be able to find the schema for the namespace of the root
> > element of an instance document, either from a schema location in the
> > instance document or from some other external means (the
> > externalSchemaLocations property of the Xerces parser, or an entity
> > resolver, for instance).
> >   4  Having found the schema for the root element, typically any others
> > needed will be found via import or include elements or schema location
> > settings in the document or parser configuration.
> >
> > In your case, schema1 imported schema2, schema2 contained the 
definition
>of
> > the root element of the document, and you specified schema1's location 
in
> > the document.  Since schema1's namespace was irrelevant to the 
validation
>of
> > the root element, there was no reason for xerces to look inside it to 
see
>if
> > it indicated where to find schema2.
> >
> > The short answer is that the processor needs to be able to find the 
schema
> > for the root element of the document.  If you have several kinds of
> > documents, with root elements in different schemas, you need to be able
> > specify the correct schema location for each one.  If the schema for 
the
> > root element depends on others, they must be specified in imports, and 
the
> > locations specified somehow (import or otherwise).  If any schema 
allows
> > wildcards or anyType, or element substitutions, or derived datatypes 
from
> > other namespaces, the locations of the schemas for those namespaces
>actually
> > referenced in the instance document must be available to the
> > parser/validator.
> >
> > Jeff
> >
> > Jeff
> > ----- Original Message -----
> > From: "Adachi Seiichi" <[EMAIL PROTECTED]>
> > To: <[EMAIL PROTECTED]>
> > Sent: Tuesday, August 26, 2003 5:15 AM
> > Subject: Re: Schema validation using multiple schemas
> >
> >
> > > Bob, Jeff,
> > >
> > > Thank you for your replies.
> > >
> > > I have 2 questions.
> > >
> > > 1.  I understand that there may be a need to specify schema#2 in the
> > > xsi:SchemaLocation of the XML file.  However, for a more complex XML
> > > schema, wouldn't this mean that you would have to specify all the
> > > schemas in each XML file?
> > >
> > > Yes, this problem can be resolved if you specify the location of
>schema#2
> > > in
> > > the XML file.  However, the XML schemas for my application will be 
more
> > > complex and I do not want to specify all the schemas that are 
involved.
> > >
> > > I am not that familiar with XML but it was my understanding that when
> > > creating an XML file, you do not need to specify the location of all 
the
> > > schema files that are declared as namespaces inside the XML file, if
> > > they are defined (imported) by the schemas that are specified in the
> > > xsi:schemaLocation of the XML file.  At least, that is what it said 
in
> > > the 2 XML Schema books I have here. (Sorry, they are in Japanese)
> > > I guess this maybe wrong. To confirm the specification on
> > > <xsi:schemaLocation> and <xsd:import> when using multiple namespaces, 
I
> > > have been looking at the w3c documents and searching the web, but 
have
> > > not found a clear answer on this topic.  Is this specified somewhere?
> > >
> > > 2.  This relates to question#1, but Xerces-J 2.5.0 is able to
> > > resolve the location of imported schema if it is not the root 
element.
> > > For example :
> > >
> > > test2.xml
> > > ---------
> > > <book xmlns='http://foo.com/namespace3'
> > >    xmlns:ns4='http://foo.com/namespace4'
> > >    xmlns:xsi='http://www.w3.org/2001/XMLSchema-instance'
> > >    xsi:schemaLocation='http://foo.com/namespace3 ns3.xsd'>
> > >       <ns4:chapter>sample XML file</ns4:chapter>
> > > </book>
> > >
> > > ns3.xsd
> > > -------
> > > <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
> > >             targetNamespace="http://foo.com/namespace3"
> > >             xmlns="http://foo.com/namespace3"
> > >             xmlns:ns4="http://foo.com/namespace4"
> > >             elementFormDefault="qualified">
> > >
> > >   <xsd:import namespace="http://foo.com/namespace4"
> > >    schemaLocation="ns4.xsd" />
> > >
> > >   <xsd:element name="book">
> > >     <xsd:complexType>
> > >       <xsd:sequence>
> > >         <xsd:element ref="ns4:chapter"/>
> > >       </xsd:sequence>
> > >     </xsd:complexType>
> > >   </xsd:element>
> > >
> > > </xsd:schema>
> > >
> > > ns4.xsd
> > > -------
> > > <xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema"
> > >             targetNamespace="http://foo.com/namespace4"
> > >             xmlns="http://foo.com/namespace4"
> > >             elementFormDefault="qualified">
> > >
> > >   <xsd:element name="chapter" type="xsd:string"/>
> > >
> > > </xsd:schema>
> > >
> > > Since this file is validated correctly, I had assumed Xerces-J 2.5.0
> > > supports these kind of files.  Is there any possibility that unable 
to
> > > resolve it in the case of the root element is a bug? (I know they are
> > > implemented differently but just as a note, Xerces-C 2.3.0 did not
> > > return any errors.) Or is this strictly an implementation dependent
> > matter?
> > >
> > > Thanks,
> > >
> > > Seiichi
> > >
> > >
> > >
> > > >From: "Jeff Greif" <[EMAIL PROTECTED]>
> > > >Reply-To: [EMAIL PROTECTED]
> > > >To: <[EMAIL PROTECTED]>
> > > >Subject: Re: Schema validation using multiple schemas
> > > >Date: Mon, 25 Aug 2003 06:51:45 -0700
> > > >
> > > >Probably xerces proceeds like this:
> > > >
> > > >Xerces must be able to directly locate the schema for the namespace 
of
> > the
> > > >root element.  It does not read schema#1 (for a seemingly irrelevant
> > > >namespace) in the hopes of finding the location of schema#2.  If
>schema
> > > #1
> > > >is in the schemaLocation attribute of the instance document, it 
should
> > > work.
> > > >You can include both schemas there if you choose.
> > > >
> > > >This is not redundant with the import element in schema#1.  That 
import
> > is
> > > >required in order to make it legal to refer in schema#1 to items 
from
> > > >schema#2.
> > > >
> > > >Jeff
> > > >
> > > >
> > > >----- Original Message -----
> > > >From: "Adachi Seiichi" <[EMAIL PROTECTED]>
> > > >To: <[EMAIL PROTECTED]>
> > > >Sent: Monday, August 25, 2003 1:39 AM
> > > >Subject: Schema validation using multiple schemas
> > > >
> > > >
> > > > > Hi All,
> > > > >
> > > > > I am trying to validate an xml file using multiple schema files
>using
> > > > > Xerces-J 2.5.0.  The xml file specifies the location of schema#1
>using
> > > > > schemaLocation.  Inside of schema#1, schema#2 is specified using
> > > > > xsd:import.  I get an error when the root element of the xml file 
is
> > an
> > > > > element defined in schema#2.
> > > > >
> > > >
> > > >
> > > 
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