Re: [xml-dev] An element with more than one possible type

[noah_mendelsohn@us.ibm.com]

I believe it's fair to say that there will likely be a number of ways of 
solving this problem in Schema 1.1, should it go forward to Recommendation 
status.  Since some of the mechanisms I have in mind have not yet been 
clearly explained in public working drafts, I'll have to hold off on 
discussing them in detail on this public list.    I expect that detailed 
proposals will be available publicly quite soon.   Roughly, you can look 
for mechanisms that will apply Schematron-like XPath predicates to the 
subtree validated by a complex type.  Furthermore, there is some chance 
that the final Recommendation will provide means for choosing the type 
itself based on the value of attribute(s) other than xsi:type.  So, if 
you're interested in a W3C XML Schema-based solution, keep an eye on the 
Schema 1.1 working drafts as they come out. 

Noah

--------------------------------------
Noah Mendelsohn 
IBM Corporation
One Rogers Street
Cambridge, MA 02142
1-617-693-4036
--------------------------------------








Rick Marshall <rjm@zenucom.com>
02/04/2007 01:22 AM
 
        To:     pau carre <pau.carre@gmail.com>
        cc:     xml-dev@lists.xml.org, (bcc: Noah 
Mendelsohn/Cambridge/IBM)
        Subject:        Re: [xml-dev] An element with more than one 
possible type


curious about this. why not the traditional data solution of an extra 
attribute specifying the type of measure? as in
<item name="water" measure="volume" value="22" />

it also opens up lots of extra, easy, possibilities for analysis.

Rick

pau carre wrote:
> I am trying to code a XML Schema (XSD file) for a web service in such 
> a way:
>
> <items>
>   <item name = "water" volume ="22">
>   <item name = "meat" weight = "10" >
> </items>
>
> It is to say, if name is "water" , then use the "volume" attribute.
> When name is "meat" then use "weight" attribute.
>
> What I have done is to define a simple type for name attribute
>
> <xs:simpleType name="nameType">
>        <xs:restriction base="xs:string">
>                <xs:enumeration value="water"/>
>                <xs:enumeration value="meat"/>
>        </xs:restriction>
> </xs:simpleType>
>
> Then I defined an abstract complex type for "item" element:
>
> <xs:complexType name="itemType" abstract = "true">
>        <xs:attribute name = "name" type = "nameType"/>
> </xs:complexType>
>
> I restricted the "name" attribute to "meat":
>
> <xs:complexType name="itemTypeMeat">
>        <xs:complexContent>
>                <xs:restriction base="itemType">
>                        <xs:attribute name = "name" type = "nameType"
> fixed="meat"/>
>                </xs:restriction>
>        </xs:complexContent>
> </xs:complexType>
>
> ... and finally I added an attribute "weight":
>
> <xs:complexType name="itemTypeMeatWeight">
>        <xs:complexContent>
>                <xs:extension base="itemTypeMeat">
>                        <xs:attribute name = "weight" type = "xs:int"/>
>                </xs:extension>
>        </xs:complexContent>
> </xs:complexType>
>
> For the "water" is the same as "meat". First I restricted the "name"
> attribute to "water":
>
> <xs:complexType name="itemTypeWater">
>        <xs:complexContent>
>                <xs:restriction base="itemType">
>                        <xs:attribute name = "name" type = "nameType"
> fixed="water"/>
>                </xs:restriction>
>        </xs:complexContent>
> </xs:complexType>
>
> ... and finally I added the "volume" attribute
>
> <xs:complexType name="itemTypeWaterVolume">
>        <xs:complexContent>
>                <xs:extension base="itemTypeWater">
>                        <xs:attribute name = "volume" type = "xs:int"/>
>                </xs:extension>
>        </xs:complexContent>
> </xs:complexType>
>
> The problem is to define the type for "item" element. If I use
> "itemType" as type it the XML does not validated because
> "itemType" is abstract. I I use:
>
> <xs:element  name="items">
>        <xs:complexType>
>                <xs:sequence>
>                        <xs:choice>
>                                <xs:element name="item"
> type="itemTypeWaterVolume"/>
>                                <xs:element name="item"
> type="itemTypeMeatWeight"/>
>                        </xs:choice>
>                </xs:sequence>
>        </xs:complexType>
> </xs:element>
>
> the XML does not validate because the validator assumes that the
> "item" type is the first defined (itemTypeWaterVolume). If I
> change the declaration of "item"  element then the validator
> assumes that the type of "item" is "itemTypeMeatWeight".
>
> Do you know how to solve this problem?
>
> Thanks in advance.
>
> Pau
>
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