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

["Pete Cordell" <petexmldev@tech-know-ware.com>]

Hi Pau,

It's not possible to do this exactly how you want.  You could use schemas 
xsi:type mechanism to approximate it.  In this case your last construct 
would be defined as:

<xs:element  name="items">
        <xs:complexType>
                <xs:sequence>
                    <xs:element name="item" type="itemType"/>
                </xs:sequence>
        </xs:complexType>
</xs:element>

and your XML instance would become:

<items>
   <item xsi:type = "itemTypeWaterVolume" volume ="22"/>
   <item xsi:type = "itemTypeMeatWeight" weight = "10" />
</items>

Although you could use simpler names if you like.  (Also your restrictions 
to itemTypeMeat and so on would not be required.)

You could also aim for something like:

<items>
   <itemTypeWaterVolume volume ="22"/>
   <itemTypeMeatWeight weight = "10" />
</items>

Other than that you would need something like Schematron (or wait for 
assertions to appear in XSD1.1!)

HTH,

Pete.
--
=============================================
Pete Cordell
Tech-Know-Ware Ltd
for XML to C++ data binding visit
http://www.tech-know-ware.com/lmx
(or http://www.xml2cpp.com)
=============================================

Original Message From: "pau carre"


>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="itemTypeWaterVolume">
>        <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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