[Request] Xerces-J: XML Schema 1.1 feature feedback

[Khaled Noaman <knoaman@ca.ibm.com>]

Hi,

The W3C Schema WG has released a last
call working draft of XML Schema 1.1 Part 1: Structures. We are considering
implementing features from this draft in Xerces-J. We would like to understand
which features users are most interested in and what scenarios they plan
on using them in.

Here's a summary of the major features
introduced in the spec:

All Group 
XML Schema 1.0 imposed many restrictions
on <all> groups. XML Schema 1.1 has relaxed several of those constraints:

• <all> groups can now be extended by adding more members to them.
• Wildcards are now allowed.
• Particles in <all> groups can now have the value of maxOccurs be greater than 1.

<xs:complexType name="applianceType">
 <xs:all>
  <xs:element name="item"
type="xs:string"/>
  <xs:element name="description"
type="xs:string"/>
 </xs:all>
</xs:complexType>

<xs:complexType name="heaterType">
 <xs:complexContent>
  <xs:extension base="applianceType">
   <xs:all>
    <xs:element name="power_in_watt"
type="xs:integer"/>
    <xs:any processContents="lax"/>
   </xs:all>
  </xs:extension>
 </xs:complexContent>
</xs:complexType>

Assertions
A form of co-occurrence constraint,
using XPath 2.0 expressions, that is associated with a complex type to
constrain element and attribute values. The list of assertions is evaluated
when a complex type is used to validate an element. 

<xs:complexType name="intRange">
 <xs:attribute name="min"
type="xs:int"/>
 <xs:attribute name="max"
type="xs:int"/>
 <xs:assert test="@min
le @max"/>
</xs:complexType>

The value of the ‘min’ attribute must
be less than the value of the ‘max’ attribute.

<xs:complexType name="arrayType">
 <xs:sequence>
  <xs:element name="entry"
minOccurs="0" maxOccurs="unbounded"/>
 </xs:sequence>
 <xs:attribute name="length"
type="xs:int"/>
 <xs:assert test="@length
eq fn:count(./entry)"/>
</xs:complexType>

The value of the ‘length’ attribute
must be equal to the number of occurrences of the ‘entry’ sub-elements.

Open Content Models
A new mechanism to allow content models
to accept elements other than those explicitly defined. The schema author
controls the degree of openness of the content model. They can specify
whether elements should be accepted everywhere or at the end of the content
model.

<xs:complexType name="name">
  <xs:openContent mode="suffix">
    <xs:any namespace="##other"
processContents="skip"/>
  </xs:openContent>
  <xs:sequence>
    <xs:element name="given"
type="xs:string"/>
    <xs:element name="middle"
type="xs:string" minOccurs="0"/>
    <xs:element name="family"
type="xs:string"/>
  </xs:sequence>
</xs:complexType>

A schema author can also define a default
open content at the schema document level, thus saving many copy/paste
if the open content is the same across the complex types.

<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.example.com/example">
  . . .
  <xs:defaultOpenContent mode="interleave">
    <xs:any processContents="lax"/>
  </xs:defaultOpenContent>
  . . .
</xs:schema>

Enhanced Wildcards
In XML Schema 1.0, a schema author was
only allowed to exclude elements and attributes from one namespace, the
target namespace,  by using ##other. In XML Schema 1.1, a schema author
can define wildcards that exclude:

• Elements and attributes from a set of namespaces by using [notNamespace]
• A particular set of qualified elements and attributes by using [notQName]
• “not-in-schema” elements and attributes (those that do not match any declaration in the schema)  by including the ##defined keyword in [notQName]

<xs:any namespace="http://www.w3.org/1999/XSL/Transform"
        xmlns:xsl="http://www.w3.org/1999/XSL/Transform"
        notQName="xsl:comment
xsl:fallback"/>

<xs:anyAttribute xmlns:ns1="http://ns1"
  notNamespace="ns1 ##targetNamespace"/>

Complex Type Restriction
The rules for checking validity of complex-type
restrictions have been simplified. The set of elements or attributes accepted
by a restriction must be a subset of those accepted by its base type.

Conditional Type Assignment
A form of co-occurrence constraint,
using XPath 2.0, that allows for a type to be assigned to an element instance
based on its properties (typically attribute values).

<xs:complexType name="valueType">
 <xs:simpleContent>
  <xs:extenstion base="xs:long">
   <xs:attribute name="kind"
type="xs:string"/>
  </xs:extension>
 </xs:simpleContent>
</xs:complexType>

<xs:element name="value"
type="valueType">
 <xs:alternative test="@kind='int'"
type="xs:int"/>
 <xs:alternative test="@kind='short'"
type="xs:short"/>
 <xs:alternative test="@kind='byte'"
type="xs:byte"/>
</xs:element>

Default Attributes
A new mechanism that makes it easier
for schema authors to include common attributes like xml:base and xml:lang
in all their content models.

<xs:schema
    xmlns:xs="http://www.w3.org/2001/XMLSchema"
    targetNamespace="http://www.example.com/example"

    defaultAttributes="defaultAttrGroup">
  . . .
</xs:schema>

Conditional Inclusion
A mechanism that allows conforming XML
Schema 1.1 processors to successfully ignore new constructs introduced
in future version of the spec. It also allows schema authors to define
schemas with newer constructs and be able to fall back to older versions
when the newer constructs are not available.

<xsd:schema 
  xmlns:xsd="http://www.w3.org/2001/XMLSchema"
  xmlns:vc="http://www.w3.org/2007/XMLSchema-versioning">

  <xsd:element name="e"
vc:minVersion="3.2">
    <!--* declaration suitable
for 3.2 
        * and later
processors *-->
  </xsd:element>
  <xsd:element name="e"

    vc:minVersion="1.1"
    vc:maxVersion="3.1">
    <!--* declaration suitable
for processors
        * supporting
versions 1.1 through 3.1
        *-->
  </xsd:element>
  ...
</xsd:schema>


We would appreciate your feedback.
 
Regards,
Khaled