"Software is commonly required to compare two URIs. Such comparisons can have two outcomes, in this document labeled "equivalent" and "different". Since URIs exist to identify resources, presumably they should be considered equivalent when they identify the same resource. This definition of equivalence is not of much practical use for reasons which include:
* Resources may have many different identifiers.
* Web architecture defines how resources are named and how their representations are interchanged, but doesn't define resource equivalence."