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MPEG-7 Problem Issues and Queries

From: Jane Hunter <jane@dstc.edu.au>
Date: Mon, 01 Jan 2001 21:19:17 +1000
Message-Id: <200101011118.f01BIsH26490@piglet.dstc.edu.au>
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?


<attribute name="myAtt" type="integer"/>

   <!-- can we expect the default value, 0, is specified
        in the following local attribute? -->
    <attribute ref="myAtt" use="default" value="0"/>

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. 

<simpleType name="referenceType">
  <union memberTypes="IDREF uriReference mpeg7:xPathType"/>

4. Union and attributes

In Sec of XML Schema Part 2, an example is given as:

  <xsd:element name='size'>
          <xsd:restriction base='integer'/>
          <xsd:restriction base='string'/>

A possible instance is:

  <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?


<element name="LinearMatrix">
      <restriction base="mpeg7:IntegerMatrixType">
        <minInclusive value="0"/>
        <maxInclusive value="65535"/>

      <attribute name="sizes" use="fixed" value="3 3"/>
        <!-- IMPOSSIBLE both extension and restriction -->



6. Is there any way to constrain the length of a locally defined 


<element name="ColorValueIndex">
    <list itemType="mpeg7:unsigned12"/>
        <!-- <length value="3"/> POSSIBLE ?? -->

   <list itemType="mpeg7:unsigned8"/>
       <!-- <minLength value="32"/> IMPOSSIBLE -->
       <!-- <maxLength value="256"/> IMPOSSIBLE -->
   <!-- </list> -->


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


9. Using derivation by restriction, can we change the content model of a group 
from choice[0,n] to sequence?

Received on Monday, 1 January 2001 06:19:24 UTC

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