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Bug 6011 - [schema11] base URI comments
Summary: [schema11] base URI comments
Status: CLOSED FIXED
Alias: None
Product: XML Schema
Classification: Unclassified
Component: Structures: XSD Part 1 (show other bugs)
Version: 1.1 only
Hardware: PC Windows XP
: P2 normal
Target Milestone: ---
Assignee: C. M. Sperberg-McQueen
QA Contact: XML Schema comments list
URL:
Whiteboard:
Keywords: resolved
Depends on:
Blocks:
 
Reported: 2008-09-02 14:21 UTC by John Arwe
Modified: 2009-01-05 15:30 UTC (History)
1 user (show)

See Also:


Attachments

Description John Arwe 2008-09-02 14:21:14 UTC
3.13.2 XML Representation of Assertion Schema Components
XML Mapping Summary for XPath Expression Property Record says
"{base URI}  The [base URI] of the host element. "
I think your existing text is OK in its use of "host element" as a kind of "parameter" within your spec.  I found no conflicting definitions at least.

1.4 Dependencies on Other Specifications simply lists Infoset as one of the dependent specs.
Appendix E Required Information Set Items and Properties (normative) lists a number of infoset properties as being required 
[base URI] has not been added it appears, and should be given your XPath expression schema component definition, no?
Not to mention schemaLocation issues from 1.0, where one might argue it should have been cited (if the timing was right wrt Infoset, but presumably it was)

4.2.2 Assembling a schema <include> clause 1
4.2.3 <redefine> clause 2
4.2.4 <override> clause 2
4.2.5.2 <import> clause 2
4.3.2 How schema definitions are located on the Web - item 3
If the schemaLocation value is a relative reference, what base URI is used to resolve it? 
[base URI] of the schemaLocation's parent element?

4.3.2 How schema definitions are located on the Web - item 3
"It is not an error for such an attempt to fail, ..."
Given the requirement on <override> (MUST resolve), is the stmt above actually true as stated any more?
I might argue the same for <redefine>.
Both 4.2.3 <redefine> clause 2 and 4.2.4 <override> clause 2 seem to contradict the unqualified "is not" above.

Note that some people have argued, very recently, that the lack of any dependency in Schema 1.0 on [XML Base], including indirectly via [base URI],
is evidence of a lack of support for XML Base within W3C and grounds for not depending on XML Base in new specs.  It would be helpful to be explicit about
the handling of base URIs in Schema 1.1 at least, so we can proceed on to newer "discussions" :-)
Comment 1 John Arwe 2008-09-11 18:43:31 UTC
The SML working group chose to endorse this bug on its call of 2008-09-11
Comment 2 C. M. Sperberg-McQueen 2008-10-30 00:05:36 UTC
The XML Schema WG discussed this issue at length during today's face to face
meeting.

In general, we are happy to make the appropriate changes and grateful to 
you for pointing out to us the need for them.  Essentially, the three points
of agreement on which we converged in today's discussion are as follows;
please push back if these seem problematic.

1) The semantics of [base URI] are as described in the XML Base spec.

This follows already from our reference to the Infoset spec (which
says that [base URI] is calculated as specified in the XML Base spec),
but we will add a note pointing out that our reference to the [base
URI] property has the consequence that in XML input, xml:base can be
used with the semantics describedin the XML Base spec.

2) The [base URI] property should be listed as one of infoset
properties we depend on.

This has been done already in connection with bug 5800.

3) Where we resolve relative URIs, they are absolutized using the
[base URI] property of the relevant element, as prescribed by the XML
Base spec.

A detailed wording proposal will be prepared by the editors.
Comment 3 John Arwe 2008-11-06 19:20:49 UTC
On 11/6 the SML working group endorsed the resolution in comment 2 without objection.
Comment 4 Sandy Gao 2008-11-21 20:49:16 UTC
During its 2008-11-21 telecon, the schema WG adopted a proposal to address the third point in comment #2.

The proposal (along with some other changes) can be found at (member-only):
http://www.w3.org/XML/Group/2004/06/xmlschema-1/structures.omni.20081121.html

With this change, the WG believes that all the issues raised in this bug report are addressed. I'm marking this RESOLVED accordingly.

John, if you would indicate your concurrence with or dissent from the
WG's disposition of the comment by closing or reopening the issue, we'll
be grateful. If we don't hear from you in the next two weeks, we'll assume
that silence implies consent.
Comment 5 John Arwe 2008-11-23 16:40:19 UTC
changes look ok (in a document of this size, some hint as to which sections to look at for changes would be helpful)

I realized in reading them that a sentence in appendix E is pretty opaque
> For interoperability, processors should accurately reflect these properties of the input to validity assessment.

"reflect"?   My understanding of the intent is that the schema processor should expose "these properties" in the infoset resulting from validity assessment, but honestly I would not (reliably, for sure) attach that intent to the words without out of band knowledge.  I encourage the editors to be less succinct in this case.  "accurately" seems odd too, it hints at unseen dragons.

Since my nominal options are reopen/close, I'll reopen to ensure this admittedly late comment is at least seen.  In the interests of "full speed ahead",

(a) I will not raise any formal objection over this no matter what the Schema wg decides to (not) do about it.  If the wg decides to make no such change, it is free to close this bug unilaterally.

(b) I will give you a concrete proposal for the editors:
For interoperability, processors should behave as if these properties were copied from the validity assessment episode's input infoset to the resulting infoset.  That is, the validity assessment episode's output infoset should expose these properties and their respective values should match the input infoset.
Comment 6 C. M. Sperberg-McQueen 2008-11-25 01:15:22 UTC
John,

Thank you for the comment on the opening paragraph of appendix E,
which for convenience I reproduce in full:

    This specification requires as a precondition for ·assessment· an
    information set as defined in [XML-Infoset].  The result of
    assessment may depend upon the following information items and
    properties. For interoperability, processors should accurately
    reflect these properties of the input to validity assessment.

The second and third sentences were inserted in a recent revision of
the text, in connection with the resolution of bug 5800 (for those who
need them, the minutes of the relevant meeting are at
http://lists.w3.org/Archives/Member/w3c-xml-schema-ig/2008Oct/0007.html).

The editors have not checked with the Working Group yet, but our
understanding of the sentence "For ... assessment" is that it means
NOT (as I think you take it)

    For interoperability, processors SHOULD expose the following
    information items and properties in their representation of the
    PSVI (and do so accurately) of the document.

but instead something more like

    For interoperability, processors SHOULD be careful to be 
    accurate in establishing the values of the following 
    information items and properties (since the result of 
    assessment depends on them).

The problem may lie in the verb "reflect", which was chosen to allow
the text to get rid of the verb "support" (which one WG member
described as "always a weasel word") but which turns out to suffer
from frailties of its own.

I think the WG should choose among the following courses of action:

1) Adopt the wording proposed by John Arwe in comment 5, which 
replaces "For ... assessment" with:

    For interoperability, processors should behave as if these
    properties were copied from the validity assessment episode's
    input infoset to the resulting infoset.  That is, the validity
    assessment episode's output infoset should expose these properties
    and their respective values should match the input infoset.

This would entail an understanding of the text which differs radically
from mine; in general, the XSD 1.1 spec works hard NOT to make any
recommendations about what PSVI information is exposed by a conforming
processor, and some WG members resisted even the proposal to provide
names for some defined subsets in Appendix D.1, on the grounds that
the names would be taken as recommendations.

2) Adopt the following alternative wording proposal, which replaces
the entire paragraph with:

    This specification requires as a precondition for ·assessment· an
    information set as defined in [XML-Infoset] which contains at
    least the following kinds of information items and properties.

This reverts to the wording of XSD 1.0, but replaces "supports" (which
is vague, and also ill matched with "information set" as its subject)
with "contains" (which is what an information set does to information
items and their properties, in the usage of the infoset spec).

3) Delete the sentence "For ... assessment" to make the paragraph
read:

    This specification requires as a precondition for ·assessment· an
    information set as defined in [XML-Infoset].  The result of
    assessment may depend upon the following information items and
    properties. 

From the fact that assessment results depend on the information items
and properties mentioned, it seems clear already that interoperability
depends on validators taking some care to get the values of the
properties right.  It is hard to imagine a reader benefiting from the
explicit exhortation that validators SHOULD do so.

For what it's worth, my own recommendation is 2, or 3.
Comment 7 David Ezell 2008-11-28 16:44:02 UTC
The WG discussed the proposals by MSM in comment #6, and chose to decide the issue using option #2.
Comment 8 John Arwe 2008-12-01 13:27:43 UTC
great, supah

(nb: I'm not sure at this point if I should be marking it resolved, or if in the Schema wg that is done by the editors to help manage workflow, so I am leaving it re-opened.  Feel free to resolve and close it once you are done with any work its existence signals a need for.)