- From: Jane Hunter <jane@dstc.edu.au>
- Date: Mon, 01 Jan 2001 21:19:17 +1000
- To: www-xml-schema-comments@w3.org
- Cc: mpeg7-ddl@darmstadt.gmd.de
Below is a list of queries raised by the MPEG-7 community whilst developing
MPEG-7 schemas. On a lot of the issues we're fairly sure of the answer already
but would be highly appreciative of definite clarification.
regards (and best wishes for 2001),
Jane Hunter
-----------------------------------------------
1. Global attributes
When referring to a global attribute whilst declaring a local attribute,
can you modify its "use" attribute value and expect this to overwrite the
original value?
Ex:
<attribute name="myAtt" type="integer"/>
<complexType>
<!-- can we expect the default value, 0, is specified
in the following local attribute? -->
<attribute ref="myAtt" use="default" value="0"/>
</complexType>
--------------------------------------------------------------------
2. Root Elements
Is there a way to specify the root element amongst global elements in an
instance document ?
-------------------------------------------------------------------
3. Union and IDREF
Each IDREF must match a corresponding ID within the XML instance document in
which it occurs. Can we expect that this rule also applies when IDREF is used
within a <union>? According to XML Schema definition, it seems not:
[Definition:] Union datatypes are those whose *value spaces* and
*lexical spaces* are the union of the value spaces and lexical
spaces of two or more other datatypes.
Ex:
<simpleType name="referenceType">
<union memberTypes="IDREF uriReference mpeg7:xPathType"/>
</simpleType>
------------------------------------------------------------------
4. Union and attributes
In Sec 2.5.1.3 of XML Schema Part 2, an example is given as:
<xsd:element name='size'>
<xsd:simpleType>
<xsd:union>
<xsd:simpleType>
<xsd:restriction base='integer'/>
</xsd:simpleType>
<xsd:simpleType>
<xsd:restriction base='string'/>
</xsd:simpleType>
</xsd:union>
</xsd:simpleType>
</xsd:element>
A possible instance is:
<size>1</size>
<size>large</size>
<size xsi:type='xsd:string'>1</size>
What happens in the last instance when "size" is also declared as an
attribute? There seems no way to specify the type using xsi:type
when the size is also an attribute.
------------------------
5. Is it possible to both extend and restrict a locally defined
datatype simultaneously?
Ex:
<element name="LinearMatrix">
<complexType>
<simpleContent>
<restriction base="mpeg7:IntegerMatrixType">
<minInclusive value="0"/>
<maxInclusive value="65535"/>
</restriction>
<attribute name="sizes" use="fixed" value="3 3"/>
<!-- IMPOSSIBLE both extension and restriction -->
</simpleContent>
</complexType>
</element>
------------------------------------------------------
6. Is there any way to constrain the length of a locally defined
list?
Ex:
<element name="ColorValueIndex">
<simpleType>
<list itemType="mpeg7:unsigned12"/>
<!-- <length value="3"/> POSSIBLE ?? -->
</simpleType>
</element>
<simpleType>
<list itemType="mpeg7:unsigned8"/>
<!-- <minLength value="32"/> IMPOSSIBLE -->
<!-- <maxLength value="256"/> IMPOSSIBLE -->
<!-- </list> -->
</simpleType>
______________________________________________________
7. When deriving a complexType by restriction on a complexType which
was itself derived by extension, must you repeat the content models of
all of the earlier base types in the type hierarchy - or do you only
need to specify the extended components?
This is a repetition of an earlier question posted on Dec 18 which has yet to
be answered.
-------------------------------------------------------
8. Is it possible to derive an abstract complexType from a non-abstract
complexType?
-------------------------------------------------------
9. Using derivation by restriction, can we change the content model of a group
from choice[0,n] to sequence?
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Received on Monday, 1 January 2001 06:19:24 UTC