Arcrole attribute

The value of the arcrole attribute must be a URI reference. It identifies some resource that describes the intended property.

<mythology     xmlns:xlink="http://www.w3.org/1999/xlink"     xlink:type="extended">    <hero       xmlns:xlink="http://www.w3.org/1999/xlink"       xlink:type="locator"       xlink:href="http://www.greece.antique/database/heracles.xml"       xlink:role="http://www.greece.antique/hero"       xlink:title="Heracles"       xlink:label="heracles">    </hero>    <god       xmlns:xlink="http://www.w3.org/1999/xlink"       xlink:type="locator"       xlink:href="http://www.greece.antique/database/zeus.xml"       xlink:role="http://www.greece.antique/god"       xlink:title="Zeus"       xlink:label="zeus">    </god>    <relation       xmlns:xlink="http://www.w3.org/1999/xlink"       xlink:type="arc"       xlink:from="zeus"       xlink:to="heracles"       xlink:arcrole="http://www.greece.antique/relations/father">    </relation>  </mythology>

Error - illegal value of the arcrole attribute

The value of the arcrole attribute must be a URI reference.

... <relation    xmlns:xlink="http://www.w3.org/1999/xlink"    xlink:type="arc"    xlink:from="zeus"    xlink:to="heracles"    xlink:arcrole="is father of"> </relation> ...

For human-readable description use title-type element(s) or attribute

The value of the arcrole attribute must be a URI reference. If more descriptive or human-readable explanation is required, the title-type element(s) or attribute can be used.

... <relation    xmlns:xlink="http://www.w3.org/1999/xlink"    xlink:type="arc"    xlink:from="zeus"    xlink:to="heracles"    xlink:arcrole="http://www.greece.antique/relations/father"    xlink:title="is father of"> </relation> ...