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Re: Semantics of a list datatype derived from another list

From: Henry S. Thompson <ht@cogsci.ed.ac.uk>
Date: 21 Mar 2001 09:56:00 +0000
To: Eddie Robertsson <eddie@allette.com.au>
Cc: Walt Yao <Walt.Yao@cl.cam.ac.uk>, xmlschema-dev@w3.org
Message-ID: <f5by9tz30pb.fsf@cogsci.ed.ac.uk>
Eddie Robertsson <eddie@allette.com.au> writes:

> Hi,
> 
> "Henry S. Thompson" wrote:
> 
> > > I am implementing a Schema parser w.r.t the 24/10/2000 version, and
> > > I run into a problem with the definition of a list datatype.  As
> > > specified in 5.1.2, "a list datatype must be derived from an atomic
> > > or a list datatype, know as the itemType of the list...".
> >
> > That's a known typo, will be corrected to 'atomic or _union_
> > datatype'.
> >
> > Re another reply, you can include a list in a union, but that still
> > doesn't allow  a list of lists -- a union used as the item type of a
> > list can't contain any lists.
> 
> I've had I look at the new specification (PR) and it says that a
> list datatype must be derived from an atomic type:
> 
> 2.5.1.2 List datatypes
> 
> "list datatypes are always derived. The value space of a list
> datatype is a set of finite-length sequences of atomic values. The
> lexical space of a list datatype is a set of literals whose internal
> structure is a white space separated sequence of literals of the
> atomic datatype of the items in the list (where whitespace matches S
> in [XML 1.0 (Second Edition)])."
> 
> My interpretation is that a list type must be derived from atomic
> types only and not atomic or union types. Is this correct?

No, sorry.  See [1]:

  "A list datatype must be derived from an atomic or a union datatype,
  known as the itemType of the list datatype."

What _I_ can't find is something which says that when the itemType is
a union, _its_ members must not be lists, which I thought was there
but which I can't find at the moment.

[1] http://www.w3.org/TR/xmlschema-2/#derivation-by-list
-- 
  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 Wednesday, 21 March 2001 04:56:05 GMT

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