- From: <noah_mendelsohn@us.ibm.com>
- Date: Fri, 6 Sep 2002 12:13:58 -0400
- To: "Sanjay Dahiya, Noida" <sanjay@noida.hcltech.com>
- Cc: xmlschema-dev@w3.org
You're most welcome. I just realized there was something quite misleading
in part of what I sent. In the example:
<schema targetNamespace="ur1" xmlns:ns1="uri1" xmlns:ns2="uri2">
<!-- Following import NOT needed -->
<import namespace="ur12"
schemaLocation="http://example.org/ns2.xsd">
<element name="ns1:outer">
<sequence>
<any processContents="lax">
</sequence>
</element
</schema>
<ns1:outer xmlns:ns1="uri1">
<ns2:inner xmlns:ns2="uri2"/>
</ns1:outer>
and especially
<ns1:outer xmlns:ns1="uri1">
<ns2:inner xmlns:ns2="uri2" schemaLocation"uri2
http://example.org/ns2b.xsd">
</ns1:outer>
The <import> is NOT needed, unless you WANT to put a schemaLocation hint
in the ur1 schema. Why? In the earlier examples, the ur1 schema
explicitly referenced an element in ur1, so the import was mandatory
there. In the <any> case, there is no explicit reference, so the import
is not needed. Hope this clarification helps.
------------------------------------------------------------------
Noah Mendelsohn Voice: 1-617-693-4036
IBM Corporation Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
------------------------------------------------------------------
"Sanjay Dahiya, Noida" <sanjay@noida.hcltech.com>
09/06/2002 03:50 AM
To: noah_mendelsohn@us.ibm.com
cc: xmlschema-dev@w3.org
Subject: RE: XML schema validation and namespaces
thanks that was real help
the reason i asked the question was that i am into making a
schema/document processor, which i initilally (for simplicity) did
for nonamespace documents, this point was not clear while moving to
multiple
namespaces
thanks again
sanjay
-----Original Message-----
From: noah_mendelsohn@us.ibm.com [mailto:noah_mendelsohn@us.ibm.com]
Sent: Friday, September 06, 2002 8:20 AM
To: Sanjay Dahiya, Noida
Cc: xmlschema-dev@w3.org
Subject: Re: XML schema validation and namespaces
Well, I can give you some general idea of how things work. First of all,
you're right, there are namespaces tbat you bump into in schema documents,
namespaces that the instance might use, and a set of rules that have to
keep straight how these all work together. The schema design goes to
great length to cover these, and it probably gives more flexibility than
you'd notice at first.
A schema document can use the <import> construction to refer to other
schema definitions for other namespaces. Optionally, the import can
supply a schemaLocation hint (and it's only a hint!) that the process MAY
choose to follow to look for the schema definitions for that other
namespace. Alternatively, the schema processor can use some other means
to figure out what schema definitions to use for that other namespace
(maybe it takes command line options, has an API, builds in definitions
for certain namespaces, etc.)
So, what happens if an instance document uses a namespace in some element
in the middle of content:
<ns1:outer xmlns:ns1="uri1">
<ns2:inner xmlns:ns2="uri2"/>
</ns1:outer>
What are the possibilities for where we get the definitions to validate
ns2:inner (presuming we had a schema for ns1?) Well, I'm too lazy to type
all the schemas exactly correctly, but if the schema for ns1 says roughly
<schema targetNamespace="ur1" xmlns:ns1="uri1" xmlns:ns2="uri2">
<import namespace="ur12">
<element name="ns1:outer">
<sequence>
<element ref="ns2:inner/>
</sequence>
</element
</schema>
then the processor will go looking for some schema document (or other
source of definitions) for ns2:inner. Exactly how is, as described above,
up to the processor. With:
<schema targetNamespace="ur1" xmlns:ns1="uri1" xmlns:ns2="uri2">
<import namespace="ur12"
schemaLocation="http://example.org/ns2.xsd">
<element name="ns1:outer">
<sequence>
<element ref="ns2:inner/>
</sequence>
</element
</schema>
then the processor MAY chose to get those definitions from
http://example.org/ns2.xsd. Another way it might get the hint is from the
instance:
<ns1:outer xmlns:ns1="uri1">
<ns2:inner xmlns:ns2="uri2" schemaLocation"uri2
http://example.org/ns2b.xsd">
</ns1:outer>
Again, it's a hint. The processor can honor the one in the import, in the
instance, neither, etc.
Now consider:
<schema targetNamespace="ur1" xmlns:ns1="uri1" xmlns:ns2="uri2">
<import namespace="ur12"
schemaLocation="http://example.org/ns2.xsd">
<element name="ns1:outer">
<sequence>
<any processContents="lax">
</sequence>
</element
</schema>
This says that outer can have most any contents. Does ns2:inner get
validated? Well, if the processor choses to find a schema, perhaps from
one of the schemaLocation hints, then the inner element does get
validated. "Lax" says: validate if you have an element declaration,
otherwise don't worry about it. "strict" (instead of lax) means "you
better have an element declaration, if not fail". "skip" means don't
validate the inner element even if you could.
To really understand this, you should find a good tutorial on schema, or
maybe even do the hard work of reading the spec (it is hard in this area.)
I hope you can see that the design provides quite a bit of power for
dealing with the situations you've raised. Many of them do arise in
various uses of XML. I hope this is helpful.
------------------------------------------------------------------
Noah Mendelsohn Voice: 1-617-693-4036
IBM Corporation Fax: 1-617-693-8676
One Rogers Street
Cambridge, MA 02142
------------------------------------------------------------------
"Sanjay Dahiya, Noida" <sanjay@noida.hcltech.com>
Sent by: xmlschema-dev-request@w3.org
09/04/2002 11:55 AM
To: xmlschema-dev@w3.org
cc: (bcc: Noah Mendelsohn/Cambridge/IBM)
Subject: XML schema validation and namespaces
Hi All
Correct me if I am wrong anywhere in the following
One can comopse an XML schema using multiple schemas and multiple
namespaces so that definitions can be reused (makes perfect sense).
For this purpose XML schema can have references to other schemas which
might have different namespaces. This is done by 'import' / 'include' tags
in the schema definition. Q1: what are the possible ways for doing the
same.
The instance document reffering to this schema would be validated by
loading other schemas and looking for corresponding definitions in those
schemas. (good so far)
Now XML instance document can also contain references to multiple
namespaces and schema using schemaLocation and
noNamespaceSchemaLocation ( why multiple ??)
Q2: XML document ( which of course must have a root element) would have
its definition in one schema only. the child elements which in case refer
to other schemas must be refered in the schema only.
Second for a validating parser what would be the precise set of rules for
locating the definition of an element that is mentioned in the instance
document.
Now to make things worse each element can refer to a namepace and supply
the prefix there itself (No idea where it is going now !!) Q3: now how
would the validating parser locate the definition of this element. and Q4:
why would someone put a namespace with an element in the instance document
and not in its schema ?
looks like some of the constructs have been designed with non-validating
parsers in mind and others for validating ones. could someone clear things
a bit here.
thanks and regards
Sanjay
Received on Friday, 6 September 2002 12:57:11 UTC