Just putting this on the record
I've just discovered a technical detail wrt xml:base attribute in RDF/XML docs - if you put a hash at the end of the base URI it is ignored when constructing relative URIs.
I.e. the following RDF/XML:
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
xml:base="http://example.com/foo#"
xmlns:rdf="#"
xmlns:rdfs="#">
<rdf:Description rdf:about="">
<rdfs:label>this</rdfs:label>
</rdf:Description>
</rdf:RDF>
gives the following triple:
<http://example.com/foordfs:label "this".
It doesn't matter if you put more than one hash at the end of the base URI, they are all ignored. I.e. the following RDF/XML:
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
xml:base="http://example.com/foo"
xmlns:rdf="#"
xmlns:rdfs="#">
<rdf:Description rdf:about="">
<rdfs:label>this</rdfs:label>
</rdf:Description>
</rdf:RDF>
gives the same triple as above:
<http://example.com/foordfs:label "this".
Note however that the absolute URI <http://example.com/spongis treated by RDF parsers as different from the absolute URI <http://example.com/spong#(which spec can verify that this?). I.e. the following RDF/XML:
<?xml version="1.0" encoding="UTF-8"?>
<rdf:RDF
xmlns:rdf="#"
xmlns:rdfs="#">
<rdf:Description rdf:about="http://example.com/spong#">
<rdfs:label>spong#</rdfs:label>
</rdf:Description>
<rdf:Description rdf:about="http://example.com/spong">
<rdfs:label>spong</rdfs:label>
</rdf:Description>
</rdf:RDF>
gives the following triples:
<http://example.com/spong#rdfs:label "spong#".
<http://example.com/spongrdfs:label "spong".
Interestingly, the URI <http://example.com/spong raises an error when using the W3C RDF validation service (running ARP) -
Error: {W107} Bad URI <http://elsewhere.org/spong: Fragment contains invalid character:#
However, Sesame 1.2.3 doesn't raise an error, and creates a new URI resource in the graph.
I remember vaguely Jeremy Carroll saying that hashes are actually allowed in fragment ids is this right or wrong?
Finally, this has implications for RDFS/WL vocabularies/ontologies that use a hash namespace, because it means we have to be careful not to confuse the 'vocabulary URI' (a.k.a. the 'ontology URI', i.e. the URI that identifies the vocabulary/ontology) and the 'namespace URI' (i.e. the actual URI you append the local name of each term to). E.g.
http://example.com/vocab - vocabulary URI.
http://example.com/vocab# - namespace URI.
For RDFS/WL vocabularies/ontologies that use a slash namespace both the vocabulary URI and the namespace URI are the same, e.g.
- vocabulary URI.
- namespace URI.
Cheers,
Al.
Alistair Miles
Research Associate
CCLRC - Rutherford Appleton Laboratory
Building R1 Room 1.60
Fermi Avenue
Chilton
Didcot
X11 0QX
United Kingdom
Email: a.j.miles (AT) rl (DOT) ac.uk
Tel: +44 (0)1235 445440

Bjoern Hoehrmann wrote:
* Miles, AJ (Alistair) wrote:
>I remember vaguely Jeremy Carroll saying that hashes are actually
>allowed in fragment ids is this right or wrong?

You have to %xx-escape them, http://example.org/## is not allowed.

I may have said that; but if I did I was wrong.
In a URI or IRI only a single # is allowed and it separates the main URI
from the fragment.

Personally, I prefer omitting any # and fragment, from an xml:base
because it is simply confusing.

Jeremy

Bjoern Hoehrmann wrote:
* Miles, AJ (Alistair) wrote:
>I remember vaguely Jeremy Carroll saying that hashes are actually
>allowed in fragment ids is this right or wrong?

You have to %xx-escape them, http://example.org/## is not allowed.

I may have said that; but if I did I was wrong.
In a URI or IRI only a single # is allowed and it separates the main URI
from the fragment.

Personally, I prefer omitting any # and fragment, from an xml:base
because it is simply confusing.

Jeremy

Bjoern Hoehrmann wrote:
* Graham Klyne wrote:
>According to RFC 3986 [1], a base URI is not permitted to have a fragment. See
>sections 5.1 and 4.3.

Though note that the value of the xml:base attribute is a string that
can be converted to a URI reference using a specific algorithm, it's
not a "Base URI" as defined in RFC 3986 though it can be transformed
into that.

Yes. xmlbase specifies:

[[
The value of this attribute is interpreted as a URI Reference as defined
in RFC 2396 [IETF RFC 2396], after processing according to Section 3.1.
]]

and then implicitly suggests dropping any fragment, since the latter
parts of the document talks about URIs rather than URI Reference.

Jeremy

Bjoern Hoehrmann wrote:
* Graham Klyne wrote:
>According to RFC 3986 [1], a base URI is not permitted to have a fragment. See
>sections 5.1 and 4.3.

Though note that the value of the xml:base attribute is a string that
can be converted to a URI reference using a specific algorithm, it's
not a "Base URI" as defined in RFC 3986 though it can be transformed
into that.

Yes. xmlbase specifies:

[[
The value of this attribute is interpreted as a URI Reference as defined
in RFC 2396 [IETF RFC 2396], after processing according to Section 3.1.
]]

and then implicitly suggests dropping any fragment, since the latter
parts of the document talks about URIs rather than URI Reference.

Jeremy