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Re: What is the meaning of the import statement?

From: Milan Trninic <mtrninic@galdosinc.com>
Date: Fri, 8 Nov 2002 11:19:33 -0800
Message-ID: <001001c2875b$c56d17f0$690aa8c0@mtrninic>
To: <Simon.Cox@csiro.au>
Cc: <www-xml-schema-comments@w3.org>, <xmlschema-dev@w3.org>
Hi again,

I was actually surprised by the simple answer I've got from you Simon that
I've completelly forgot the initial problem I've started from. Slightly
modified drawing is attached.
In essence if I wa to create an application location schema, and try to
import weather and transportation, the validation will fail.
Once the base schema is imported through environment schema, it will not be
imported again through transportation one. So a needed subset of the base
schema will be ignored.
If I use your solution Simon, that means that I have to analyze all schemas
that I work with and find all dependencies on other schemas (namespaces) and
create stubs for each of them.
Now, this exactly is the reason I've mentioned scalability in one of the
first emails. Once there are large "networks" of dependant schemas, it is
not going to be easy for an application depveloper to analyze manually ALL
schemas in the network that his schema depends on. Don't you think so?

Milan
=========================================
Milan Trninic
Senior Software Engineer
tel: 1 604 484-2764, 484-2750
mtrninic@galdosinc.com
Galdos Systems IncT http://www.galdosinc.com
=========================================
===============
Privileged or confidential information may be contained in this message. If
this message was not intended for you, destroy it and notify us immediately.
Opinions, conclusions, recommendations, and other information presented in
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  ----- Original Message -----
  From: Simon.Cox@csiro.au
  To: mtrninic@galdosinc.com
  Cc: www-xml-schema-comments@w3.org ; xmlschema-dev@w3.org
  Sent: Tuesday, November 05, 2002 20:31
  Subject: RE: What is the meaning of the import statement?



  Milan - You state:
  "What transportation folks need is another stub schema in the base set
that
  will include the two they require. But the problem is they do not controll
  the base set. So they cannot do it. "
  I think this is where you are going wrong.

  The last statement is incorrect and does not follow from anything in your
  previous statement or the specs.  There is nothing stopping you writing a
  stub schema targetting someone else's namespace that merely includes two
  schema documents targetting the same namespace.  There is no violation of
  consistency or integrity in allowing anyone to assemble their own subset
of
  components from any namespace by creating a stub schema that includes a
  subset of the schema documents that define components in that namespace.
I
  use this trick all the time in creating GML application schemas - I create
  stub documents called featureAndValue.xsd, coverageAndTemporal.xsd etc as
I
  need them. Then I only have a single <import> for the components from the
  GML namespace.


  -----Original Message-----
  From: Milan Trninic [mailto:mtrninic@galdosinc.com]
  Sent: Wednesday, 6 November 2002 12:58 AM
  To: Henry S. Thompson
  Cc: www-xml-schema-comments@w3.org; xmlschema-dev@w3.org
  Subject: Re: What is the meaning of the import statement?


  Henry et al,

  I have tried to capture my problem in a gif drawing. I hope it goes
through.
  The explanation follows:

  So there are various schema sets, each controlled by a different
authority.
  There is base, transportation, environment, location, and presumably large
  number of other application specific sets.

  Now look at the Transportation - Base dependencies. There are two imports
  that import two modules from the base set of schemas. This will not work.
  What transportation folks need is another stub schema in the base set that
  will include the two they require. But the problem is they do not controll
  the base set. So they cannot do it. The only way out is that people that
  created the base set created at the very beggining the stub schema that
  includes ALL schemas from the set. That would be useful for others. But
  importing all definitions when you don't need all si not the best option.

  Any thoughts on this?

  Regards

  Milan
  =========================================
  Milan Trninic
  Senior Software Engineer
  tel: 1 604 484-2764, 484-2750
  mtrninic@galdosinc.com
  Galdos Systems IncT http://www.galdosinc.com
  =========================================
  ===============
  Privileged or confidential information may be contained in this message.
If
  this message was not intended for you, destroy it and notify us
immediately.
  Opinions, conclusions, recommendations, and other information presented in
  this message are not given or necessarily endorsed by my employer or firm.


  ----- Original Message -----
  From: "Henry S. Thompson" <ht@cogsci.ed.ac.uk>
  To: "Milan Trninic" <mtrninic@galdosinc.com>
  Cc: <www-xml-schema-comments@w3.org>; <xmlschema-dev@w3.org>
  Sent: Monday, November 04, 2002 2:04 AM
  Subject: Re: What is the meaning of the import statement?


  > "Milan Trninic" <mtrninic@galdosinc.com> writes:
  >
  > > I've been pondering on one issue related to the multiple <import>s of
  the
  > > same namespace. Here is the story in short:
  > >
  > > I wanted to modularize the definitions in our namespace and to import
  them
  > > selectivelly from the application schemas. (Application meaning the
  schemas
  > > built on top of our base schemas). And I've figured I can't since the
  > > specification allows processors to ignore all but the first <import>
  > > statement of the particular namespace.
  > >
  > > On the other hand, the specification allows processors to take into
the
  > > account all of the imports as well. And this is what some of the
  processors
  > > do. This incostistent behaviour is the first problem.
  > >
  > > But ok, if applications always use only one <import> statement, that
  > > incostistency goes away.
  >
  > Right, that's the sensible defensive strategy.
  >
  > > Now, this obviously means that we are importing the namespace (with
all
  of
  > > its definitions), not the definitions themselves. But then, why do we
  need
  > > two attributes there? Why schemaLocation? I mean if the namespace is
  always
  > > bound to only one schema location, that attribute is completelly
  redundand.
  >
  > Sorry, how does it get bound to _any_ schema location?  Answer -- the
  > spec. provides a range of options for processor and/or user to
  > employ/specify, everything from "nothing, because I've got that one
  > built in" through "try derefing the NS name" to "use schemaLoc".
  >
  > > The existence of that attribute and the fact that it is not required
  that
  > > anything actually exists at the end of the namespace URI produces the
  > > conclusion that <import> does not really import the namespace (with
all
  of
  > > its definitions), but imports specific definitions from it.
  > >
  > > Now which one is correct?
  >
  > Neither.  The fundamental purpose of <xs:import namespace='nsName'> is
  > to allow references (e.g. ref=, base=) to names qualified by nsName.
  >
  > > Even with this issue resolved, the fact that you cannot modularize the
  > > schemas is a real problem. Acheving scalability is affected. Building
  > > mutually dependant, "networked" or hierarchical schema sets from
  different
  > > domain and for different purposes is significantly affected. I mean
this
  > > almost means that I have to have different namespace for each of my
  > > definitions.
  >
  > There is a tradeoff here, but the common approach to this is to go
  > ahead and modularise, and use <xs:include> to manage the
  > modularisation (that's what _it_ is meant for).  In the case of
  > importing a modularly-defined schema, that does mean you have to
  > create a stub schema document which consists entirely of
  > <xs:include>s, which you then point to from the schemaLoc of your
  > import.
  >
  > Hope this helps.
  >
  > ht
  > --
  >   Henry S. Thompson, HCRC Language Technology Group, University of
  Edinburgh
  >           W3C Fellow 1999--2002, part-time member of W3C Team
  >      2 Buccleuch Place, Edinburgh EH8 9LW, SCOTLAND -- (44) 131 650-4440
  >     Fax: (44) 131 650-4587, e-mail: ht@cogsci.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]
  >





Received on Friday, 8 November 2002 14:20:10 GMT

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