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Re: XPath/XQuery - Typed Value Determination

• To: Alan Gutierrez <alan-xml-dev@e...>
• Subject: Re: XPath/XQuery - Typed Value Determination
• From: Vladimir Gapeyev <vgapeyev@s...>
• Date: Thu, 20 Oct 2005 21:54:56 -0400 (EDT)
• Cc: xml-dev@l...
• In-reply-to: <20051021002658.GE3303@m...>
• References: <20051021002658.GE3303@m...>

On Thu, 20 Oct 2005, Alan Gutierrez wrote:

>    I'm confused by the wording of...
>
>    http://www.w3.org/TR/xpath-datamodel/#TypedValueDetermination
>
>    ...where it discusses the value value determination for lists.
>
>    "For each of these lexical forms, the type of the corresponding
>    item is found in {item type definition}."
>
>    I can't figure out if the {item type definition} is attached to
>    the list as a property, or an index property, or if it attached
>    to the item within the list. The mention of recursion implies
>    the latter.

I think one would need a larger quote to understand the question...:

    "The types of the items in the typed value of a node are determined by
     a recursive process called typed value determination. This process
     begins with T, the schema type of the node itself, as represented in
     the PSVI. The type T has a variety, which is either atomic, union, or
     list. The typed value determination process is defined as follows:

      <skip other cases>

     - If the {variety} of T is list, the [schema normalized value] of the
       node is considered to be a space-separated list of lexical forms,
       each of which has its own type. For each of these lexical forms, the
       type of the corresponding item is found in {item type definition}.
       This type is then substituted for T, and the typed value
       determination process is invoked recursively for each member of the
       list."

Brief answer: {item type definition} is a property of T, the schema's list 
_type_ that validated the value in question.  It is not a property the 
list _value_.

One could arrive to this understanding after meditating over WXS Part 2, 
4.1.1  http://www.w3.org/TR/xmlschema-2/#rf-defn

[I tried to find a description of Typed Value Determination in XQuery 
Formal Semantics, but apparently it just refers to the above-quoted 
definition (see 3.5.2, 
http://www.w3.org/TR/2005/WD-xquery-semantics-20050915/#id-typed-value)
Too bad.  I guess, the reason is that formalizing this notion would 
require formalizing most of WXS, which is any formalist's nightmare!]

Vladimir

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