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Subject: RE: [ubl-cmsc] restriction and extension are both subclassing
- From: Matthew Gertner <matthew.gertner@schemantix.com>
- To: "'Burcham, Bill'" <Bill_Burcham@stercomm.com>,'Eduardo Gutentag' <eduardo.gutentag@sun.com>
- Date: Thu, 02 May 2002 11:01:18 +0200
I
agree that extension of a base type can be described as specialization. I
heartily disagree that the resulting type has a value set that is a subset of
that of the base type. Can you can provide an example of values valid in
the base type but not in the extended type?
Matt
Maybe these two references will help:
(From the category theory perspective) Start at
section 2.3 of this paper.
There are two examples in that section of specialization by adding
attributes (properties) to the subtypes -- and the explanation is from the
set-theoretic perspective.
(From Entity-Relationship Modeling perspective)
Start at slide
56 in this presentation.
To your point about the value of this "pure
theory analysis" -- Matt G. presented an alternative Specialization
Architecture in the CMSC today -- the one described in his recent paper
(Schema Adjunct Framework + Schematron). As a motivator for the value of
that architecture, Matt said essentially "restriction and extension are two
very different things and the way XSD tries to treat them both as derivation
is just wrong -- so we shouldn't use XSD". Sorry I didn't include that
context with my post, but as a rebuttal argument I'd say it isn't just "pure
theory analysis" -- I'd say instead that it is rebuttal.
-----Original Message-----
From: Eduardo Gutentag
[mailto:eduardo.gutentag@sun.com]
Sent:
Wednesday, May 01, 2002 5:47 PM
To: Burcham, Bill
Cc:
'ubl-cmsc@lists.oasis-open.org'
Subject: Re: [ubl-cmsc] restriction and
extension are both subclassing
> "Burcham, Bill"
wrote:
>
> Since I couldn't get this thought out in the conference
call today, I thought I'd get in into the record this way:
>
>
From the set-theoretic standpoint, XSD restriction of a simple type and
extension of a complex type are the same -- they both define a subset of a
base set. To use type terminology, they are both kinds of specialization in
the generalization-specialization paradigm.
>
> A simple type is
single-valued -- think scalar. When we restrict a scalar type we take away
values from its domain. This means that the restricted type has fewer possible
values than the original (or base) type. We never add values to the domain. An
example of this kind of specialization is: base type Integer, specialized type
Whole Number. These are scalars and the set of Whole Numbers is a proper
subset of the set of Integers.
>
> A complex type is not
single-valued. Instead it is comprised of one or more (simple type or complex
type). A complex type can be specialized in two ways: 1) a constituent simple
type can be restricted or 2) a property of simple or complex type can be
added. In both cases, the new type has fewer possible (compound) values than
the original type. Note: that transitivity in the definition of complex type
means that there is kind of a third way to specialize a complex type: (3) a
constituent complex type can
> be specialized.
>
>
I
totally fail to see how a complex type that has been "specialized" by
having
a property of either type added has fewer possible values. I just
don't see
it. No. Nope. What am I missing?
(and I have to confess
that, even if the assertion were true, I fail to see
what is the value
added of this kind of pure theory analysis - undoubtedly
the result of a
mind that wears glazed eyes at all times and carries an extra
pair just in
case...)
--
Eduardo
Gutentag
| e-mail:
eduardo.gutentag@Sun.COM
XML Technology
Center
| Phone: (510)
986-3651
Sun Microsystems
Inc.
|
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