- From: Henry S. Thompson <ht@inf.ed.ac.uk>
- Date: Mon, 12 Oct 2009 16:39:33 +0100
- To: "XMLSchema at XML4Pharma" <XMLSchema@XML4Pharma.com>
- Cc: <xmlschema-dev@w3.org>
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Stimulated in equal measure by this thread, and a request from the XML
Security WG [0], I came up with my personal 'best practice' guideline
for schema document design for multi-namespace schemas. I include the
core bit below -- for the full context and a worked example, see my
reply to the DSIG WG [1].
ht
[0] http://lists.w3.org/Archives/Public/public-xmlsec/2009Oct/0019.html
[1] http://lists.w3.org/Archives/Public/public-xmlsec/2009Oct/0023.html
- -------------------------
HST's best practice guide for multiple-namespace schema composition
It's helpful in discussions of this sort to be careful with
vocabulary:
Schema document: An XML document in the W3C XML Schema namespace
Schema: An abstract data object, typically composed from one or more
schema documents according to the rules given in the W3C XML
Schema specs.
A schema document specifies either one or no target namespace.
A schema may well contain element & attribute declarations and/or type
definitions for many target namespaces.
The W3C XML Schema specs provide a number of mechanisms for assembling
the schema documents needed to construct a schema for a particular
validation episode:
1) the schemaLocation attribute on xs:include elements.
2) xsi:schemaLocation (in the instance to be validated);
3) the schemaLocation attribute on xs:import elements;
4) the namespace URIs themselves (in the instance to be validated, or
from the namespace attribute on xs:import elements);
Without going into the details of what's optional and what's required,
or of the range of choices implementations exhibit, here's my
recommendation for multi-namespace schemas:
1) For each namespace in your language, there should be one primary
schema document. It may be the only schema document for that
namespace, or it may use xs:include (which must have a
schemaLocation attribute) to allow for modular development by
including multiple as-it-were secondary schema documents;
2) Whenever reference is made to names in another namespace from a
primary or secondary schema document, use an xs:import _without_ a
schemaLocation attribute;
3) Create a driver schema document, whose target namespace is the
namespace of the (most common) document element of instance
documents in the language. It should contain an xs:include of the
primary schema document for that namespace, and xs:imports for all
the other namespaces, _with_ schemaLocation attributes pointing to
the primary schema documents for those other namespaces.
Then, by passing the ___location of the driver schema document to schema
validation tools and/or by including an xsi:schemaLocation attribute
on the document element of instances to be validated which associates
the target namespace of the driver schema document with its ___location,
you will get the behaviour you need from all the tools/implementations
I am aware of.
Schematically, this looks like
driver.xsd -- TNS = http://www.example.org/rootNS
/|\
/ | \
/ | \
/ | \
xs:include | \
schemaLoc= | \
/ | \
/ xs:import \
/ NS=...NS2 \
/ schemaLoc= \
/ | xs:import
/ | NS=...NS3
/ | schemaLoc=
/ | \
primary1.xsd primary2.xsd primary3.xsd
TNS=...rootNS TNS=...NS2 TNS=...NS3
/ \ /|\
/ \ / | \
/ \ / | \
/ \ / | \
xs:import xs:import / | \
NS=...NS2 NS=...NS3 xs:include | \
schemaLoc= | \
/ | \
3.1.xsd | \
xs:include \
schemaLoc= \
| \
3.2.xsd \
xs:include
schemaLoc=
|
3.3.xsd
- --
Henry S. Thompson, School of Informatics, University of Edinburgh
Half-time member of W3C Team
10 Crichton Street, Edinburgh EH8 9AB, SCOTLAND -- (44) 131 650-4440
Fax: (44) 131 651-1426, e-mail: ht@inf.ed.ac.uk
URL: http://www.ltg.ed.ac.uk/~ht/
[mail really from me _always_ has this .sig -- mail without it is forged spam]
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Received on Monday, 12 October 2009 15:40:18 UTC