Dave Reynolds wrote:
On Mon, 2011-01-17 at 16:51 +0100, Martin Hepp wrote:
Dear all:
RFC 2616 [1, section 3.2.3] says that
"When comparing two URIs to decide if they match or not, a client
SHOULD use a case-sensitive octet-by-octet comparison of the entire
URIs, with these exceptions:
- A port that is empty or not given is equivalent to the default
port for that URI-reference;
- Comparisons of host names MUST be case-insensitive;
- Comparisons of scheme names MUST be case-insensitive;
- An empty abs_path is equivalent to an abs_path of "/".
Characters other than those in the "reserved" and "unsafe" sets (see
RFC 2396 [42]) are equivalent to their ""%" HEX HEX" encoding.
For example, the following three URIs are equivalent:
http://abc.com:80/~smith/home.html
http://ABC.com/%7Esmith/home.html
http://ABC.com:/%7esmith/home.html
"
Does this also hold for identifying RDF resources
a) in theory and
No. RDF Concepts defines equality of RDF URI References [1] as simply
character-by-character equality of the %-encoded UTF-8 Unicode strings.
Note the final Note in that section:
"""
Note: Because of the risk of confusion between RDF URI references that
would be equivalent if derefenced, the use of %-escaped characters in
RDF URI references is strongly discouraged.
"""
which explicitly calls out the difference between URI equivalence
(dereference to the same resource) and RDF URI Reference equality.
I'd suggest that it's a little more complex than that, and that this may
be an issue to clear up in the next RDF WG (it's on the charter I believe).
For example:
When a URI uses components of the generic syntax, the component
syntax equivalence rules always apply; namely, that the scheme and
host are case-insensitive and therefore should be normalized to
lowercase. For example, the URI <HTTP://www.EXAMPLE.com/> is
equivalent to <http://www.example.com/>.
- http://tools.ietf.org/html/rfc3986#section-6.2.2.1
However, that's only for URIs which use the generic syntax (which most
URIs we ever touch do use).
It would be great if a normalized-IRI with specific normalization rules
could be drafted up as part of the next WG charter - after all they are
a pretty pivotal part of the sem web setup, and it would be relatively
easy to clear up these issues.
Best,
Nathan
