John,

You can't enforse this using Xml Schema.  However, if both elements are 
required and the attributes, in both cases, are required and fixed, why do 
you need the attributes?  If you have a business reason to require those 
attributes, does the order matter?  You can create a global type that allows 
both values ("data" and "tra1") and require two reference elements in the 
sequence and then use a uniqueness constraint (xs:unique) to make sure that 
URI attributes are unique.  Alternatively you can rename the elements to 
something like reference-data and reference-tra1.

-- 
Stan Kitsis
Program Manager, XML Technologies
Microsoft Corporation

This posting is provided "AS IS" with no warranties, and confers no rights. 
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"John Smith" <john.smith@m...> wrote in message 
news:g83Zf.1507$oj5.597142@n......
>
> Can you suggest me some solution? I was thinking that it is enough for XML 
> parser to differ elements by its position: first and second.
>
> Thank you.
>
>
>
> "swapna guddanti [MSFT]" <swapnag@m...> wrote in message 
> news:443402ea$1@n......
>> hi,
>> you cannot have two elements with the same name in the same scope that
>> differ only in attributes.
>> Reason:
>> A content model must be formed such that during validation of an element,
>> the items inside it can be uniqhely determined without examining the 
>> content
>> or attributes of that item.
>>
>> hope this helps,
>> swapna
>>
>>
>> "John Smith" <john.smith@m...> wrote in message
>> news:z1LYf.1475$oj5.582887@n......
>>>
>>> I have created a schema, but I got an error validating it. Is it 
>>> possible
>> to
>>> have 2 ds:Reference elements (with different attributes)?
>>>
>>> Error message:
>>>
>>> Element "ds:Reference" occurs more than once in the same content model 
>>> but
>>> does not refer to top-level type definition.
>>>
>>> Schema:
>>>
>>> <schema xmlns="http://www.w3.org/2001/XMLSchema"
>>> xmlns:ds="http://www.w3.org/2000/09/xmldsig#"
>>> targetNamespace="http://www.w3.org/2000/09/xmldsig#"
>>> elementFormDefault="qualified" version="0.1">
>>> <!-- Basic Types Defined for Signatures -->
>>> <simpleType name="CryptoBinary">
>>> <restriction base="base64Binary"/>
>>> </simpleType>
>>> <!-- Start Signature -->
>>> <element name="Signature" type="ds:SignatureType"/>
>>> <complexType name="SignatureType">
>>> <sequence>
>>> <element ref="ds:SignedInfo"/>
>>> <element ref="ds:SignatureValue"/>
>>> <element ref="ds:KeyInfo"/>
>>> </sequence>
>>> <attribute name="Id" type="string" use="required" fixed="sig1"/>
>>> </complexType>
>>> <element name="SignatureValue" type="ds:SignatureValueType"/>
>>> <complexType name="SignatureValueType">
>>> <simpleContent>
>>> <extension base="base64Binary">
>>> <attribute name="Id" type="ID" use="optional"/>
>>> </extension>
>>> </simpleContent>
>>> </complexType>
>>> <!-- Start SignedInfo -->
>>> <element name="SignedInfo" type="ds:SignedInfoType"/>
>>> <complexType name="SignedInfoType">
>>> <sequence>
>>> <element ref="ds:CanonicalizationMethod"/>
>>> <element ref="ds:SignatureMethod"/>
>>> <element name="Reference">
>>> <complexType>
>>> <sequence>
>>> <element ref="ds:DigestMethod"/>
>>> <element ref="ds:DigestValue"/>
>>> </sequence>
>>> <attribute name="URI" type="anyURI" use="required" fixed="#data1"/>
>>> </complexType>
>>> </element>
>>> <element name="Reference">
>>> <complexType>
>>> <sequence>
>>> <element ref="ds:DigestMethod"/>
>>> <element ref="ds:DigestValue"/>
>>> </sequence>
>>> <attribute name="URI" type="anyURI" use="required" fixed="#tra1"/>
>>> </complexType>
>>> </element>
>>> </sequence>
>>> <attribute name="Id" type="ID" use="optional"/>
>>> </complexType>
>>> <element name="CanonicalizationMethod"
>>> type="ds:CanonicalizationMethodType"/>
>>> <complexType name="CanonicalizationMethodType" mixed="true">
>>> <attribute name="Algorithm" type="anyURI" use="required"/>
>>> </complexType>
>>> <element name="SignatureMethod" type="ds:SignatureMethodType"/>
>>> <complexType name="SignatureMethodType" mixed="true">
>>> <attribute name="Algorithm" type="anyURI" use="required"/>
>>> </complexType>
>>> <element name="DigestMethod" type="ds:DigestMethodType"/>
>>> <complexType name="DigestMethodType" mixed="true">
>>> <attribute name="Algorithm" type="anyURI" use="required"/>
>>> </complexType>
>>> <element name="DigestValue" type="ds:DigestValueType"/>
>>> <simpleType name="DigestValueType">
>>> <restriction base="base64Binary"/>
>>> </simpleType>
>>> <!-- End SignedInfo -->
>>> <!-- Start KeyInfo -->
>>> <element name="KeyInfo" type="ds:KeyInfoType"/>
>>> <complexType name="KeyInfoType" mixed="true">
>>> <choice>
>>> <element ref="ds:X509Data"/>
>>> </choice>
>>> <attribute name="Id" type="ID" use="optional"/>
>>> </complexType>
>>> <!-- Start X509Data -->
>>> <element name="X509Data" type="ds:X509DataType"/>
>>> <complexType name="X509DataType">
>>> <sequence>
>>> <choice>
>>> <element name="X509Certificate" type="base64Binary"/>
>>> </choice>
>>> </sequence>
>>> </complexType>
>>> <!-- End X509Data -->
>>> <!-- End KeyInfo -->
>>> <!-- End Signature -->
>>> </schema>
>>>
>>>
>>
>>
>
>