Allow only other existing XML values in XSD? (xs:key and xs:keyref)

Question

Let\'s take the following example XML:

  NiceDevice
  123


  

        

Answer 1

Use xs:key and xs:keyref to constrain usesDevices to have a value of a device name:

Then this XML will be valid:

  
    NiceDevice
    123
  
  
    user1
    NiceDevice
  
  
    user2
    NiceDevice
  

But this XML,

  
    NiceDevice
    123
  
  
    user1
    NiceDevice
  
  
    user2
    BadDevice
  

will not,

[Error] try.xml:16:5: cvc-identity-constraint.4.3: Key 'deviceKeyRef' with value 'BadDevice' not found for identity constraint of element 'r'.

as requested.

Note that I've added to your XML a single root element, which is required for your XML to be well-formed.