XML : Putting in a link in XML with XLink but the link address contains entities and operators

I am trying to put a link into my xml. The link directs it to the student handbook. This is part of my XML

  <?xml version="1.0" encoding="UTF-8" standalone="yes" ?>      <units xmlns:xlink="http://www.w3.org/1999/xlink">              <unit>                  <unit_code>code</unit_code>                  <unit_title>unit title</unit_title>                  <unit_coordinator>Title fname sname</unit_coordinator>                  <unit_outline xlink:type="simple" xlink:href="http://www.ecu.edu.au/handbook/unit?id=CSP2103&year=2016">http://www.ecu.edu.au/handbook/unit?id=CSP2103&year=2016</unit_outline>              </unit>      </units>    

The problem is that when I try to validate this XML it says that 'year' is an unassigned and not a default entity. The '=' is also an error cause it is not referenced to anything. My question is how do I use the link and is there anything missing from my codes ?