[xquery-talk] about "module" in XQuery spec
he harrison
harrison076 at gmail.com
Fri Jan 11 11:00:54 PST 2008
Thank you Michael, seems we are now getting closer about this issue.
We all agree that modules in XQuery could be compiled independently.
(Original definition:A *module* is a fragment of XQuery code
that conforms to the Module
<http://www.w3.org/TR/xquery/#doc-xquery-Module>grammar and can
independently undergo
the static analysis phase
<http://www.w3.org/TR/xquery/#dt-static-analysis>described in
*2.2.3 Expression
Processing*<http://www.w3.org/TR/xquery/#id-expression-processing>.
)
Then to what extent this definition "can independently undergo
the static analysis phase
<http://www.w3.org/TR/xquery/#dt-static-analysis>" should be followed?
Is it an optional feature of module, or a strict rule for any XQuery
implementation?
This two choices will lead to two design---although for "normal" case the
two
designs will show no difference, but still the two designs are different in
essence, and will
show different behavior under some special case such as "redefine".
For example, if we consider it's a strict rule, then any design
that could not be implemented in independent module compilation
should be considered as not conformant to spec.
Otherwise, we have to consider that, "can independently undergo
the static analysis phase
<http://www.w3.org/TR/xquery/#dt-static-analysis>" is an optional
feature of XQuery's module.
Harrison
2008/1/11, Michael Kay <mike at saxonica.com>:
>
> You are quite correct that the XQuery specification says nothing about
> how xs:redefine is handled. This was a deliberate choice, the WG discussed
> the matter and decided that nothing useful could be said. This is because
> the specification quite deliberately doesn't say, in the case of "import
> schema", where the schema components are obtained from, and this means that
> if (as in this case) there are different versions of the schema components
> available then it's not defined (by the specification) which version is
> loaded.
>
> I think there are two possibilities:
>
> (a) both modules use the same schema components for namespace *
> http://www.w3.org/XQueryTest/simple*, which must be the post-redefine
> components. In this case the answer is true.
>
> (b) the two modules use different schema components for namespace
> http://www.w3.org/XQueryTest/simple - one gets the pre-redefine
> components, the other gets the post-redefine version. This violates the
> consistency requirements documented in the specification; the specification
> says that in this situation the results are completely undefined. Clearly a
> good processor will detect the inconsistency and refuse to run the query,
> but the spec makes it clear that anything might happen - it's like
> submitting a random binary file to the Java VM.
>
> If you're a user, the clear implication is: don't do this.
>
> If you're an implementor, the implication is: either ensure that both
> modules use the post-redefine version of the type (which probably isn't
> feasible if the modules are compiled separately). Alternatively, detect and
> report the inconsistency if you can, but your product is not nonconformant
> if you don't.
>
> Incidentally, it's no different from having the two modules import the
> schema from different locations and picking up different versions; it
> doesn't require xs:redefine to trigger this problem.
>
> You're right that XSLT handles the issue quite differently. XSLT builds a
> single schema that serves all modules, both statically and dynamically. This
> has the disadvantage that it makes independent compilation of modules
> extremely difficult. But then, it's almost impossible to compile modules
> independently in XSLT anyway.
>
> Michael Kay
> http://www.saxonica.com/
>
> ------------------------------
> *From:* talk-bounces at x-query.com [mailto:talk-bounces at x-query.com] *On
> Behalf Of *he harrison
> *Sent:* 09 January 2008 02:48
> *To:* talk at x-query.com
> *Subject:* [xquery-talk] about "module" in XQuery spec
>
> Hi,
> I come up with a problem when reading XQuery1.0 spec., following is my
> case:
>
> a.xq:
>
> module namespace ma=" http://www.w3.org/TestModules/moduleA";
> import schema namespace simple=" http://www.w3.org/XQueryTest/simple " at
> "schema_a.xsd";
> declare function ma:funcA()
> {
> "40" cast as simple:myType
> };
>
> b.xq:
>
> declare namespace mb=" http://www.w3.org/TestModules/moduleB ";
> import module namespace ma="http://www.w3.org/TestModules/moduleA" at "
> a.xq";
> import schema namespace simple=" http://www.w3.org/XQueryTest/simple" at
> "schema_b.xsd";
>
> declare function mB:funcB()
> {
> ma:funcA() instance of simple:myType
> };
>
> <result>{mb:funcB()}</result>
>
> schema_a.xsd:
>
> <xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
> xmlns:simple=" http://www.w3.org/XQueryTest/simple "
> targetNamespace="http://www.w3.org/XQueryTest/simple"
> elementFormDefault="qualified" attributeFormDefault="qualified"
>
> >
> <xs:simpleType name = "myType">
> <xs:restriction base = "xs:int">
> <xs:minInclusive value = "1"/>
> <xs:maxInclusive value = "50"/>
> </xs:restriction>
> </xs:simpleType>
> </xs:schema>
>
> schema_b.xsd:
>
> <xs:schema xmlns:xs=" http://www.w3.org/2001/XMLSchema "
> xmlns:simple="http://www.w3.org/XQueryTest/simple"
> targetNamespace=" http://www.w3.org/XQueryTest/simple "
> elementFormDefault="qualified" attributeFormDefault="qualified"
> >
> <redefine
> schemaLocation="schema_a.xsd">
> <extension base="simple:myType">
> <xs:minInclusive value = "51"/>
> <xs:maxInclusive value = "100"/>
> </extension>
> </redefine>
> </xs:schema>
>
> What would be the result of this case?
> true? false? runtime error? or implementation define?
> Or in another word, would the type in module a.xq should
> be redefined by module c.xq's imported schema definition?
>
> This case is related with how to understand the XQuery's "module".
>
> Let me give my understanding:
> XSLT's module, in my understanding, should be "included" in
> another module to compile, could not be compiled independently,
> in other words, it's a "white box", its semantic
> depends on where it's included or imported(because its schema type could
> be
> differently redefined in different including or importing module).
>
> While I think XQuery's module is different with XSLT's module, I think
> XQuery spec.
> allow its module be compiled independently, no matter where the module is
> imported,
> module's semantic should not be changed, in other words, XQuery's module
> is a "black box", wherever module is imported, module's schema type
> definition should not be
> affected by type redefine mechanism.
>
> The reason why I make such conclusion is from following XQuery spec
> statement:
> 1 "A module import <http://www.w3.org/TR/xquery/#dt-module-import> imports
> only functions and variable declarations; it does not import other objects
> from the imported modules, such as in-scope schema definitions<http://www.w3.org/TR/xquery/#dt-issd>or statically
> known namespaces <http://www.w3.org/TR/xquery/#dt-static-namespaces>. Module
> imports are not transitive¡ªthat is, importing a module provides access
> only to function and variable declarations contained directly in the
> imported module."
>
> Here XQuery's statement is clearly different with XSLT's statement about
> module import.
> In XSLT spec, module imports are transitive while XQuery clearly stated
> that they
> are not, so XQuery's module import must be something different with XSLT's
> module import.
> My thought is, XQuery's module is a "black box" while XSLT's module is a
> "white box"
>
> 2 "It is a static error <http://www.w3.org/TR/xquery/#dt-static-error> [
> err:XQST0036 <http://www.w3.org/TR/xquery/#ERRXQST0036>] to import a
> module if the importing module's in-scope schema types<http://www.w3.org/TR/xquery/#dt-is-types>do not include definitions for the schema type names that appear in the
> declarations of variables and functions (whether in an argument type or
> return type) that are present in the imported module and are referenced in
> the importing module."
>
> Here spec. force user to import interface needed schema types, if we
> consider XQuery's
> module as "white box", then all imported types in "white box" has already
> imported, then
> this statement seems lead to redundancy, however if we consider XQuery's
> module
> as a "black box", then this statement is quite nature to understand.
>
> Could someone offer me some comment?
> Many thanks!
>
>
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