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Re: clarification/errata: circular attributeGroup, ur-type & include

From: Stanley Guan <Stanley.Guan@oracle.com>
Date: Thu, 25 Oct 2001 12:25:29 -0700
Message-ID: <3BD86729.BB7557A0@oracle.com>
CC: www-xml-schema-comments@w3.org, xmlschema-dev@w3.org
I think, to answer the following questions, we need to take good
practice of doing modularization and composition of schemas into
consideration.  And, should be enfornced  by the standard if possible!

sandygao@ca.ibm.com wrote:

> Hi Henry,
> Thanks for the reply.
> Further on this topic:
> 1. If schema document A includes B, and B includes C. Does A have access to
> components in C? And does C have access to A?

In this case, A depends on B and B depends on C.  A good design will enforce
that A can access declarations and definitions provided in B, not C.  Schema C
should be hidden from B's user.

The alternative way of exposing C to A is by doing:
   A includes B and C. (in this case, B should not depends on C).

For the question -- "Does C have access to A", I think, from design point of
view, it's a bad practice (i.e., violating the purpose of modularization).  This
creates interdependecy between C and A.

> I think the answer is yes, according to your explanation below.
> 2. If schema document A includes B, and B *imports* C. Does A have access
> to components in C?

Same as above.  A good practice will not allow A to access C directly (note
that A can still access C indirectly via B).

The alternative design will be:
   A includes B and imports C.  But, this could be a bad design if B still
   depends on C for its definitions.  If B still depends on C, the user of B
   must always import C which is a bad design.

> From the spec [1], it seems A can't access C. But I want to be sure about
> it. And if the above (1) is true, I would think (2) is true too.
> [1] http://www.w3.org/TR/xmlschema-1/#src-resolve
> Schema Representation Constraint: QName resolution (Schema Document)
> ...
> 4 its ·namespace name· is either the target namespace of the schema
> document containing the ·QName· or that schema document contains an
> <import> element information item the ·actual value· of whose namespace
> [attribute] is identical to that ·namespace name·.
> Thanks,
> Sandy Gao
> Software Developer, IBM Canada
> (1-905) 413-3255
> sandygao@ca.ibm.com
>                     ht@cogsci.ed.a
>                     c.uk (Henry S.       To:     Sandy Gao/Toronto/IBM@IBMCA
>                     Thompson)            cc:     xmlschema-dev@w3.org, www-xml-schema-comments@w3.org
>                                          Subject:     Re: clarification/errata: circular attributeGroup,
>                     10/24/2001            ur-type & include
>                     06:41 AM
>                     Please respond
>                     to ht
> sandygao@ca.ibm.com writes:
> > [3] include
> >
> > Assume schema document A includes schema documents B and C, where B has
> the
> > same target namespace as A does, and C has no target namespace. Then from
> > within a certain document, components from which document(s) can be
> > referred to? That is, how to fill the following table? (R(A,B)=Y means
> > components in A can refer to components in B.)
> > R A B C
> > A Y Y Y
> > B ? Y ?
> > C ? ? Y
> >
> > >From the spec, it seems that B can refer to A (bullet 4 of QName
> resolution
> > (Schema Document)). How about the other question marks?
> The WG discussed your questions, and requested me to answer this one.
> All three documents contribute components to and resolve their
> references in the single target namespace, so all cells in the table
> should be 'Y'.
> This results from lazy resolution of references and the impact of
> so-called 'chameleon' include (A, with a target namespace, includes C,
> which does not, with the consequence that C's components are defined
> in A's target namespace, and C's unqualified references are redirected
> to that namespace as well).
> If there are specific places in the text of the spec. which encourage
> other conclusions, please let us know and we'll try to improve them.
> ht
> --
>   Henry S. Thompson, HCRC Language Technology Group, University of
> Edinburgh
>           W3C Fellow 1999--2001, 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/
Received on Thursday, 25 October 2001 15:26:11 UTC

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