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RE: Substitution groups: Is the "or" in "restriction or extension " ex clusive?

From: Mark Feblowitz <mfeblowitz@frictionless.com>
Date: Fri, 11 Jan 2002 08:53:00 -0500
Message-ID: <4DBDB4044ABED31183C000508BA0E97F024D56DD@fcpostal.frictionless.com>
To: "'Jeni Tennison'" <jeni@jenitennison.com>
Cc: "Xmlschema-Dev (E-mail)" <xmlschema-dev@w3.org>
So, as I read this, as long as each step (DD derived from D derived from B)
is a valid derivation, then it is ok for dd of type DD to be in the
substitution group b of type B, regardless of whether all of the derivation
steps use the same subset of {extension, restriction}. Is that correct?

(BTW, I don't quite understand number 1 below - could you explain?).
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Mark Feblowitz                                   [t] 617.715.7231
Frictionless Commerce Incorporated     [f] 617.495.0188 
XML Architect                                     [e]
mfeblowitz@frictionless.com
400 Technology Square, 9th Floor 
Cambridge, MA 02139 
www.frictionless.com  
 

 -----Original Message-----
From: 	Jeni Tennison [mailto:jeni@jenitennison.com] 
Sent:	Friday, January 11, 2002 4:24 AM
To:	Mark Feblowitz
Cc:	Xmlschema-Dev (E-mail)
Subject:	Re: Substitution groups: Is the "or" in "restriction or
extension" ex  clusive?

Hi Mark,

> For example, if I use the common practice of performing derivation
> by extension and derivation by restriction in separate steps, can
> the result of such a two-step derivation be the legal type of a
> substitution group member?

Yes, no problem. The type must be 'validly derived'. The definition of
'validly derived' in detailed in:

Schema Component Constraint: Type Derivation OK (Complex)

For a complex type definition (call it D, for derived) to be validly
derived from a type definition (call this B, for base) given a subset
of {extension, restriction} all of the following must be true:

1 If B and D are not the same type definition, then the {derivation
method} of D must not be in the subset.
2 One of the following must be true:
2.1 B and D must be the same type definition. 
2.2 B must be D's {base type definition}. 
2.3 All of the following must be true:
2.3.1 D's {base type definition} must not be the ·ur-type definition·. 
2.3.2 The appropriate case among the following must be true:
2.3.2.1 If D's {base type definition} is complex, then it must be
validly derived from B given the subset as defined by this constraint.
2.3.2.2 If D's {base type definition} is simple, then it must be
validly derived from B given the subset as defined in Type Derivation
OK (Simple) (§3.14.6).

                   http://www.w3.org/TR/xmlschema-1/#cos-ct-derived-ok

Note that the substitution group exclusions (what types are allowed)
get passed down the chain of types. So if the head element has
final="extension" then the type of the member element must not have
been derived by extension in any of the derivation steps.
                   
Cheers,

Jeni

---
Jeni Tennison
http://www.jenitennison.com/
Received on Friday, 11 January 2002 08:53:34 GMT

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