XML Linking Language (XLink) Version 1.0 W3C REC (2001-06-27), 5.1.3 Traversal Rules for an Extended Link (arc-Type Element):
... The arcrole attribute corresponds to the [RDF] notion of a property, where the role can be interpreted as stating that "starting-resource HAS arc-role ending-resource." This contextual role can differ from the meaning of an ending resource when taken outside the context of this particular arc. For example, a resource might generically represent a "person," but in the context of a particular arc it might have the role of "mother" and in the context of a different arc it might have the role of "daughter."