N00b question: unique attributes

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May 29th, 2009, 04:42 PM

TheJim01

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N00b question: unique attributes

What I'm trying to do: Provide a schema-based method of creating unique values of my "id" attribute. I'll be referencing them later.

I've been to the end of Google and back, and as far as I can tell I'm creating a valid schema for limiting the ids, but when I try to break the XML, it continues to validate.

I validated my schema with the W3C validator.

I validate my XML with XMLCopy, and have the schema associated with the XML document.

Here are my files:
test.xsd

XML Code:

Original - XML Code

<?xml version="1.0" encoding="UTF-8"?>
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema" 
targetNamespace="http://www.blahblahblah.tv/NS"
xmlns="http://www.blahblahblah.tv/NS"
elementFormDefault="qualified">
 
  <xs:complexType name="somethingType">
    <xs:attribute name="id" type="xs:nonNegativeInteger"/>
  </xs:complexType>
 
  <xs:complexType name="rootType">
    <xs:sequence>
      <xs:element name="something" type="somethingType" maxOccurs="unbounded"/>
    </xs:sequence>
  </xs:complexType>
 
  <xs:element name="root" type="rootType">
    <xs:key name="blahKey">
      <xs:selector xpath="./something"/>
      <xs:field xpath="@id"/>
    </xs:key>
  </xs:element>
  
</xs:schema>

test.xml

XML Code:

Original - XML Code
<?xml version="1.0" encoding="UTF-8"?> <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://www.blahblahblah.tv/NS" xsi:schemaLocation="http://www.blahblahblah.tv/NS test.xsd"> <something id="0" /> <something id="1" /> <something id="1" /> </root>

<?xml version="1.0" encoding="UTF-8"?>
 
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://www.blahblahblah.tv/NS"
xsi:schemaLocation="http://www.blahblahblah.tv/NS test.xsd">
 
<something id="0" />
<something id="1" />
<something id="1" />
 
</root>

The XML file validates, even though my key should force the "id" attribute of "something" elements to be unique.

They're very simple, so I'm obviously missing something trivial--I just can't put my finger on it. Is my validator not working correctly? If so, what would you recommend?

May 30th, 2009, 12:45 PM

xml-profi

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<xsd:attribute name="id" type="xsd:ID" use="required"/>

xsd:ID

A1
not start with numbers

Comments on this post

TheJim01 agrees: Danke schön

__________________
Helmut Hagemann Germany

wer lesen und google kann ist klar im Vorteil
who can read and google is a clear advantage

June 1st, 2009, 09:31 AM

TheJim01

if(a==b && b==c) a=c;

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I understand that your suggestion implements the standard formatting for IDs, and forces each to be unique (based on the NCName data type from DTD). However, I would like to use a number as my unique ID, which means I can't use this datatype. As an example, consider detailing a list of books, where each book's IBSN will be its unique identifier. This usage would not allow the use of xsd:ID for the unique identifier field.

Every tutorial I've seen indicates this is possible by using xsd:unique or xsd:key to indicate an element or attribute is unique, regardless of data type. I chose xsd:key because I will be referencing my data at a later point. When that didn't work, I tried using xsd:unique, but that validates the bad XML just like xsd:key.

I suppose an important aspect to consider is my attribute does not need to use the name "id". For all purposes, the attribute could be named "isbn", "modelNumber", or "telephoneNumber"--it really doesn't matter. All that matters is that I have a numbers-only field that validates unique values.

June 2nd, 2009, 05:47 AM

xml-profi

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better answer

hello again

http://www.zvon.org/xxl/XMLSchemaTu...r_keys_st4.html

learning by doing

Code:


<xsd:schema xmlns:xsd="http://www.w3.org/2001/XMLSchema" >

  <xsd:element name="root" type="myList">
    <xsd:unique name="myId">
      <xsd:selector xpath="./a"/>
      <xsd:field xpath="id"/>
    </xsd:unique>
    <xsd:unique name="myart">
      <xsd:selector xpath="./a"/>
      <xsd:field xpath="@art"/>
    </xsd:unique>
  </xsd:element>

  <xsd:complexType name="myList">
    <xsd:sequence minOccurs="1">
      <xsd:element name="a" minOccurs="1" maxOccurs="unbounded">
      
        <xsd:complexType>
          <xsd:sequence minOccurs="1">
            <xsd:element name="id" type="xsd:NCName" nillable="true"/>
            
          </xsd:sequence>
          <xsd:attribute name="art" type="xsd:nonNegativeInteger" use="required"/>
        </xsd:complexType>
        
      </xsd:element>
    </xsd:sequence>
    
  </xsd:complexType>
  
</xsd:schema>

Code:


<?xml version="1.0" encoding="UTF-8"?>
<root xsi:noNamespaceSchemaLocation="einzig.xml" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance">
	<a art="1">
		<id>a</id>
	</a>
	<a art="2">
		<id>f</id>
	</a>
	<a art="3">
		<id>d</id>
	</a>
</root>

Helmut Hagemann

June 2nd, 2009, 10:37 AM

TheJim01

if(a==b && b==c) a=c;

Join Date: Feb 2004

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I agree, learning by doing is a very good way to learn.

I re-wrote the XSD and XML. After trying several methods of forcing validation errors, I found a significant difference between code that correctly enforces the key, and code that doesn't.

The issue lies in the namespaces. For my first attempt, I declared a target namespace in the schema, and referenced that namespace in the XML file (as I did above). The schema would enforce types, for example xsd:nonNegativeInteger would cause id="-1" to cause an error. The schema would not enforce keys, for example two elements of the same type with id="1" would not cause an error.

When I removed the namespace from the schema, and used xsi:noNamespaceSchemaLocation in the XML, it enforced both types and keys.

I found it hard to believe that keys are intended to be implemented without namespaces, so I did some more digging. I found that xpath tends to ignore default namespaces. To fix this, I updated my schema with a declared namespace, pointing to the default namespace. I then updated my xpath variables with the named default namespace prefix, and validation was successful. I also noticed that I only needed to add the prefix to the selector path, but that could have been a fluke in my simple schema.

My final working example is below:

test.xsd:

XML Code:

Original - XML Code

<?xml version="1.0" encoding="UTF-8"?>
 
<xs:schema xmlns:xs="http://www.w3.org/2001/XMLSchema"
targetNamespace="http://blah.com/NS"
xmlns="http://blah.com/NS"
xmlns:tns="http://blah.com/NS"
elementFormDefault="qualified">
 
<xs:element name="root" type="rootType">
  <xs:key name="someKey">
    <xs:selector xpath="./tns:someNode"/>
    <xs:field xpath="@uniqueId"/>
  </xs:key>
</xs:element>
 
<xs:complexType name="rootType">
  <xs:sequence>
    <xs:element name="someNode" type="someType" minOccurs="1" maxOccurs="unbounded"/>
  </xs:sequence>
</xs:complexType>
 
<xs:complexType name="someType">
  <xs:attribute name="uniqueId" type="xs:nonNegativeInteger"/>
</xs:complexType>
 
</xs:schema>

test.xml:

XML Code:

Original - XML Code
<?xml version="1.0" encoding="UTF-8"?> <root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xmlns="http://blah.com/NS" xsi:schemaLocation="http://blah.com/NS asdf.xsd"> <someNode uniqueId="0"/> <someNode uniqueId="1"/> <someNode uniqueId="2"/> </root>

<?xml version="1.0" encoding="UTF-8"?>
 
<root xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xmlns="http://blah.com/NS"
xsi:schemaLocation="http://blah.com/NS asdf.xsd">
 
<someNode uniqueId="0"/>
<someNode uniqueId="1"/>
<someNode uniqueId="2"/>
 
</root>

Changing one of the uniqueID values to anything but a positive integer will now cause validation to fail.

Thank you very much for your help.

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