On Jan 31, 2005, at 7:10 PM, Martin Duerst wrote:
5) Add a note saying something like "Comparison functions provided by many URI classes/implementations make additional assumptions about equality that are not true for Identity Constructs. Atom processors therefore should use simple string functions for comparing Identity Constructs." I think such a note could be a good balance to the normalization advice.
That would be a falsehood. Identifiers are not subject to "simplification" -- they are either equivalent or not. We can add all of the implementation requirements we like to prevent software from detecting false negatives, but that doesn't change the fact that equivalent identifiers always identify the same resource. It is the author's responsibility to use URIs (or IRIs) that are actually different, not the responsibility of the protocol or implementation.
I am disappointed that a MUST requirement was added to IRI in the last draft without working group review. This part
Applications using IRIs as identity tokens with no relationship to a protocol MUST use the Simple String Comparison (see section 5.3.1). All other applications MUST select one of the comparison practices from the Comparison Ladder (see section 5.3 or, after IRI-to-URI conversion, select one of the comparison practices from the URI comparison ladder in [RFC3986], section 6.2)
is completely missing the point of the ladder. The identifiers may or may not be equivalent and there is absolutely no reason for protocols to require inaccurate comparisons. The reason for simplification of comparison is ONLY that false negatives are an acceptable fact of life and their elimination is an implementation-specific decision that has no impact on interoperable use of identifiers. That is why there is no such requirement for URIs.
....Roy
