Re: Strict and lax schema validation (PR#87)

Hi Erik,

Based on your further explanations as well as explanations from Michael
Sperberg-McQueen, the working group resolved to adopt the default of lax schema
processing for initializing the schema validation episode.  Furthermore, the
applicability of schema definitions is based on this definition with the
*requirement* to recursively descend when a schema declaration is not found for
an element.  This mirrors the wording in XSLT 2.0.

The editor's draft now reflects this information in the model element
definition, and an informative note was added to the revalidate event to point
to the definition.

Best regards,
John Boyer

> 
> All,
> 
> XForms 1.1 mentions in 4.3.5:
> 
>      "the node satisfies all applicable XML schema definitions
>      (including those associated by [...] an external or an inline
>      schema [...])
> 
> I would like a precision on what "applicable" means for schema types
> when types are not assigned with xforms:bind or xsi:type. If I do a
> correct job below, then you will see that things are currently not
> clear.
> 
> Assume a schema defining types in the:
> 
>     xmlns:foo="http://example.org/schema/foo"
> 
> namespace (that schema does not import other schemas). I import the
> schema into a model with three instances:
> 
>     <xforms:model schema="foo.xsd">
> 
>       <xforms:instance id="instance-1">
>         <foo:form>
>           ...
>         </foo:form>
>       </xforms:instance>
> 
>       <xforms:instance id="instance-2">
>         <bar:form>
>           ...
>         </bar:form>
>       </xforms:instance>
> 
>       <xforms:instance id="instance-3">
>         <foo:undefined>
>           ...
>         </foo:undefined>
>       </xforms:instance>
> 
>     </xforms:model>
> 
> Assume foo.xsd defines only a complex type for foo:form, but no type
> for foo:undefined, and no type for bar:form (bar maps to a different
> namespace, and there is no schema for "bar").
> 
> It seems to me that foo:form for sure has an "applicable" schema
> definition. So no problem here.
> 
> Now what's the algorithm for bar:form? It certainly doesn't have any
> schema definition: there is no schema for namespace "bar". So I guess
> this means there is no "applicable" definition for bar:form. However,
> you could decide to recurse the tree and validate further, or not.
> 
> Now what about foo:undefined? There is a schema for namespace "foo",
> but none for the type foo:undefined. Does this mean there there is an
> applicable definition or not? Same thing, you could decide to recurse
> the tree and validate further, or not.
> 
> Now I shouldn't even have to discuss this in these terms, because XML
> schema provides options already, see "3.10.1 The Wildcard Schema
> Component" in [1].
> 
> There are three ways you can process a subtree in schema:
> 
>     *strict*
> 
>       There must be a top-level declaration for the item available, or
>       the item must have an xsi:type, and the item must be ?valid? as
>       appropriate.
> 
>     *skip*
> 
>       No constraints at all: the item must simply be well-formed XML.
> 
>     *lax*
> 
>       If the item has a uniquely determined declaration available, it
>       must be ?valid? with respect to that definition, that is,
>       ?validate? if you can, don't worry if you can't.
> 
> So it seems to me that here the question is whether we process
> instances with "strict" or "lax" processing (and possibly "skip" as
> well).
> 
> XSLT 2.0 solves the problem by providing a "validation" attribute [2]
> which can have value "strict", "lax", and two others ("preserve" and
> "strip") which are probably not relevant here.
> 
> XSLT 2.0 also provides a "type" attribute, exclusive with
> "validation". In XForms, we have a similar situation: we can
> explicitly bind a type to the root element of an instance with
> xforms:bind or with xsi:type. If we do, everything is fine. If we
> don't, THEN we want to specify whether we want strict or lax
> validation.
> 
> It seems to me then, if my understanding is correct, that there is an
> omission in XForms at this point regarding how validation is
> performed. We should:
> 
> 1. Explicitly specify whether instance validation is performed in
>      "strict" or "lax" mode when no type is assigned to the root element
>      of the instance.
> 
> 2. Ideally, provide an option to specify whether "strict", "lax" or
>      even "skip" mode is applied. This could be done with a simple
>      attribute on xforms:instance:
> 
>        <xforms:instance validation="lax">
> 
> 3. Possibly, also provide the option for "skip" mode, to specifically
>      exclude an instance from validation.
> 
> Comments on this are of course welcome.
> 
> -Erik
> 
> [1] http://www.w3.org/TR/xmlschema-1/
> [2] http://www.w3.org/TR/xslt20/#validation
> 
> -- 
> Orbeon Forms - Web Forms for the Enterprise Done the Right Way
> http://www.orbeon.com/
> 
>

Received on Monday, 5 November 2007 23:03:20 UTC