RE: relative uri references

But hasn't Peter just shown us that all URIs are essentially absolute? Given this fact, all URIs can be round-tripped without any
problem.

	Boris

> -----Original Message-----
> From: Alan Ruttenberg [mailto:alanruttenberg@gmail.com]
> Sent: 24 November 2008 16:22
> To: Boris Motik
> Cc: Peter F. Patel-Schneider; ivan@w3.org; public-owl-wg@w3.org
> Subject: Re: relative uri references
> 
> Hi Boris,
> 
> I want to reiterate my concern about the issue of relative URIs in
> imports. Having things defined so that these can not possibly be round
> tripped would be a real problem.
> 
> -Alan
> 
> On Mon, Nov 24, 2008 at 11:14 AM, Boris Motik
> <boris.motik@comlab.ox.ac.uk> wrote:
> > Hello,
> >
> > I think this is actually much better. Given that we can't have relative IRIs anyway, there is no
> point in not having the default
> > prefix defined. Hence, I've changed the spec according to your suggestion.
> >
> > Regards,
> >
> >        Boris
> >
> >> -----Original Message-----
> >> From: Peter F. Patel-Schneider [mailto:pfps@research.bell-labs.com]
> >> Sent: 24 November 2008 15:39
> >> To: ivan@w3.org
> >> Cc: boris.motik@comlab.ox.ac.uk; alanruttenberg@gmail.com; public-owl-wg@w3.org
> >> Subject: Re: relative uri references
> >>
> >> Actually the structural specfication uses IRIs (from RFC 3987) as
> >> identifiers (but it calls them URIs - section 2.3).  My reading of
> >> RFC3987 http://www.ietf.org/rfc/rfc3987.txt has an IRI as absolute and
> >> has an optional fragment (at least, IRI has the same expansion as
> >> absolute-IRI plus an optional fragment).  Thus the structural
> >> specfication is correct with respect to the need for absolute URIs.
> >>
> >> In the functional syntax (section 2.3) one can use
> >> - an IRI - which is absolute and allows fragments
> >> - a curie - which is the combination of
> >>   - a optional namespace name - which expands to an IRI
> >>   - an irelative-ref - which is appended to the IRI
> >>
> >> The only issue then is ontologies that use curies with no namespace
> >> names in documents that do not have a namespace expansion for the empty
> >> namespace.  The rule for this just uses the irelative-ref, which can
> >> result in a relative URI (but this is forbidden because "[t]he full URI
> >> obtained by this expansion must be a valid URI" [Section 3.2.1.]).
> >>
> >> Therefore the following document is not a valid OWL 2 ontology:
> >>    Ontology(foo)
> >> because the ontology URI does not expand into a valid IRI.
> >>
> >> However, in my view it would be better to be more clear, by modifying
> >> the CURIE expansion rules at the end of 3.2.1 as follows.
> >>
> >> * If the prefix of the CURIE is not present, then
> >>   prefix definitions of the ontology document being parsed MUST contain
> >>   a definition of the empty (missing) prefix. The resulting
> >>   full URI is obtained by concatenating the namespace with the CURIE's
> >>   reference.
> >> * If the prefix of the CURIE is present, then either Table 2 or the
> >>   prefix definitions of the ontology document being parsed MUST contain
> >>   a definition for the prefix. The resulting
> >>   full URI is obtained by concatenating the namespace with the CURIE's
> >>   reference.
> >>
> >> peter
> >>
> >>
> >> From: Ivan Herman <ivan@w3.org>
> >> Subject: Re: relative uri references
> >> Date: Mon, 24 Nov 2008 15:49:59 +0100
> >>
> >> > Boris,
> >> >
> >> > at the moment, the syntax document says that OWL uses URIs for
> >> > identifiers which are more than just symbols. And yes, one of the core
> >> > approach on the Semantic Web is to use URIs (well, plus bnodes and
> >> > literals, but let us put that aside as they are not relevant for the
> >> > discussion). So I would propose to that on the structural level we
> >> > indeed have full blown, ie, absolute URIs.
> >> >
> >> > Ivan
> >> >
> >> > Boris Motik wrote:
> >> > > Hello,
> >> > >
> >> > > Well, it is clear that in the context of Internet protocols, relative URIs don't make sense:
> you
> >> can't make a GET request from a
> >> > > relative URI; instead, you always need an enclosing base URI to do so.
> >> > >
> >> > > From a logic point of view, however, a URI is nothing more than a symbol. Thus, a URI
> <blah.owl>
> >> is a symbol that is completely
> >> > > different from, say, <http://www.example.com/blah.owl>. These two URIs are not identical, so
> >> there is no problem from a logical
> >> > > point of view. In other words, from a logical point of view, URIs are just symbols, and we
> don't
> >> care whether they are absolute or
> >> > > relative.
> >> > >
> >> > > I don't know whether this may be objectionable from a Semantic Web point of view. This
> question
> >> is not as relevant to the
> >> > > functional-style syntax as it is relevant to the structural specification (after all, FS just
> >> encodes the structural specification).
> >> > > There, we are currently not requiring URIs to be absolute -- that is, we are allowing classes
> >> that are fully identified with the
> >> > > relative URI <blah.owl>. Note that, <blah.owl> is in this case the full name of the class, so
> you
> >> shouldn't perform any expansion.
> >> > >
> >> > > To summarize, we need to decide whether it is OK to have classes that are completely
> identified
> >> by a relative URI. If we ban them
> >> > > from the structural specification, then the FS should just follow suit.
> >> > >
> >> > > Regards,
> >> > >
> >> > >   Boris
> >> > >
> >> > >> -----Original Message-----
> >> > >> From: Ivan Herman [mailto:ivan@w3.org]
> >> > >> Sent: 24 November 2008 13:02
> >> > >> To: Boris Motik
> >> > >> Cc: 'Alan Ruttenberg'; 'W3C OWL Working Group'
> >> > >> Subject: Re: relative uri references
> >> > >>
> >> > >> Hi Boris,
> >> > >>
> >> > >> I actually tried to re-read what you wrote in your original reply and, I
> >> > >> must admit, I am not sure I understand. You say:
> >> > >>
> >> > >> [[[
> >> > >>                                In the functional-style syntax ontology
> >> > >> documents, only namespace declarations are expanded, and relative URIs
> >> > >> are not expanded. I think this is correct: we never say that the URIs of
> >> > >> ontology entities must be absolute. Thus, if someone actually creates
> >> > >> ontology entities with relative URIs, the functional-style syntax will
> >> > >> correctly capture this.
> >> > >>
> >> > >> Note that URIs have a well-defined identity. Therefore, a relative URI
> >> > >> provides a perfect way of identifying some ontology entity - that is, it
> >> > >> is a URI just like any other.
> >> > >> ]]]
> >> > >>
> >> > >> What I do not understand is your statement that 'relative URI [...] is a
> >> > >> URI just like any other'.
> >> > >>
> >> > >> Looking at the URI spec (I use the Apache version because it has nice
> >> > >> hyperlinks built in),
> >> > >>
> >> > >> http://labs.apache.org/webarch/uri/rfc/rfc3986.html#relative-ref
> >> > >>
> >> > >> says that a relative URI expresses a 'real' URI (they call it target URI
> >> > >> there) using the references resolution mechanism in
> >> > >>
> >> > >> http://labs.apache.org/webarch/uri/rfc/rfc3986.html#reference-resolution
> >> > >>
> >> > >> which also says that
> >> > >>
> >> > >> [[[
> >> > >> relative references are only usable when a base URI is known. A base URI
> >> > >> must be established by the parser prior to parsing URI references that
> >> > >> might be relative.
> >> > >> ]]]
> >> > >>
> >> > >> According to
> >> > >>
> >> > >> http://labs.apache.org/webarch/uri/rfc/rfc3986.html#base-retrieval
> >> > >>
> >> > >> [[[
> >> > >> If no base URI is embedded and the representation is not encapsulated
> >> > >> within some other entity, then, if a URI was used to retrieve the
> >> > >> representation, that URI shall be considered the base URI.
> >> > >> ]]]
> >> > >>
> >> > >> Ie, a relative URI is not a 'URI just like any other', it makes sense
> >> > >> only in term of a base URI (which can be, of course, a file:/// URI of
> >> > >> the encapsulating file). This is not dependent on the syntax used.
> >> > >>
> >> > >> As a consequence, I believe that a relative URI in a FS syntax document
> >> > >> should be viewed as an abbreviation for a full URI with the file name or
> >> > >> retrieval URI of that FS document serving as a base. This is by no means
> >> > >> different from what happens in the M'ter syntax, OWL/XML, RDF/XML, or
> >> > >> Turtle.
> >> > >>
> >> > >> If all this is true, then introducing a @base to the FS and the M'ter
> >> > >> syntax does make sense if we want a final control over the exact
> >> > >> interpretation of the relative URI-s in the FS.
> >> > >>
> >> > >> (Alternatively, we could say that the base URI for a relative URI is the
> >> > >> Ontology URI if it exists, but I am not 100% sure that mixing
> >> > >> functionalities on that level is wise.)
> >> > >>
> >> > >> Cheers
> >> > >>
> >> > >> Ivan
> >> > >>
> >> > >>
> >> > >> Boris Motik wrote:
> >> > >>> Hello,
> >> > >>>
> >> > >>> The main difficultly I see is that turning base off on a particular subset of the document
> >> might
> >> > >> not be straightforward. You might
> >> > >>> need to turn base off in case you really want to use relative Uris to identify entities. Now
> in
> >> > >> XML, this is not difficult because
> >> > >>> any element can contain xml:base; hence, you can always locally turn xml:base off by placing
> >> > >> xml:base on the element with its value
> >> > >>> equal to some opaque URI. To simulate that, we'd need to be able to enclose arbitrary
> subsets
> >> of
> >> > >> the FS document into a local base
> >> > >>> declaration. It is doable, but I wonder whether it is worth the trouble.
> >> > >>>
> >> > >>> Note that in FS you can have a default namespace. Although this is not identical to xml:base
> >> (for
> >> > >> example, this default namespace is
> >> > >>> not affected by the physical URI of the document, and namespace expansion is by simply
> pasting
> >> the
> >> > >> prefix rather than using URI
> >> > >>> resolution algorithm), it achieves a similar goal as xml:base: you can write most of the
> URIs
> >> in
> >> > >> the document without prefixing them
> >> > >>> with any namespace.
> >> > >>>
> >> > >>> Please let me know if you consider this insufficient.
> >> > >>>
> >> > >>> Regards,
> >> > >>>
> >> > >>>         Boris
> >> > >>>
> >> > >>>> -----Original Message-----
> >> > >>>> From: Ivan Herman [mailto:ivan@w3.org]
> >> > >>>> Sent: 24 November 2008 11:49
> >> > >>>> To: Boris Motik
> >> > >>>> Cc: 'Alan Ruttenberg'; 'W3C OWL Working Group'
> >> > >>>> Subject: Re: relative uri references
> >> > >>>>
> >> > >>>> Boris,
> >> > >>>>
> >> > >>>> did we ever consider adding a 'base', like 'xml:base', to the functional
> >> > >>>> and the m'ter syntaxes?
> >> > >>>>
> >> > >>>> Note that this is the only difference, for example, between the turtle
> >> > >>>> specification as a team submission[1] and the earlier turtle
> >> > >>>> specification: the former introduced a @base directive (alongside the
> >> > >>>> @prefix ones). It might make sense to do this for the FS and M'Ter.
> >> > >>>>
> >> > >>>> Just a thought
> >> > >>>>
> >> > >>>> Ivan
> >> > >>>>
> >> > >>>>
> >> > >>>>
> >> > >>>> [1] http://www.w3.org/TeamSubmission/turtle/
> >> > >>>>
> >> > >>>> Boris Motik wrote:
> >> > >>>>> Hello,
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> In the RDF syntax, the resolution of URI references is governed fully by
> >> > >>>>> the underlying RDF format. For example, if you are working with RDF/XML,
> >> > >>>>> then the RDF parser should use xml:base. In addition, the XML parser
> >> > >>>>> will expand any XML entities as well. There is no equivalent of the
> >> > >>>>> Namespace declaration in the RDF syntax.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> In the XML Syntax, there are no Namespace declarations either. Again,
> >> > >>>>> you have is xsd:base for relative URIs, and this is explicitly mentioned
> >> > >>>>> in the document. Furthermore, we don't need a specific URI abbreviation
> >> > >>>>> mechanism is because XML Syntax ontology documents can use XML entities
> >> > >>>>> for abbreviation of long URIs.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> The functional-style syntax and the Manchester syntax, in contrast,
> >> > >>>>> cannot rely on other specifications (such as RDF of XML) for
> >> > >>>>> abbreviation and expansion of URI references, so they need their own URI
> >> > >>>>> resolution mechanisms. In the functional-style syntax ontology
> >> > >>>>> documents, only namespace declarations are expanded, and relative URIs
> >> > >>>>> are not expanded. I think this is correct: we never say that the URIs of
> >> > >>>>> ontology entities must be absolute. Thus, if someone actually creates
> >> > >>>>> ontology entities with relative URIs, the functional-style syntax will
> >> > >>>>> correctly capture this.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> Note that URIs have a well-defined identity. Therefore, a relative URI
> >> > >>>>> provides a perfect way of identifying some ontology entity - that is, it
> >> > >>>>> is a URI just like any other.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> Hence, it seems to me that we don't really need to say anything more
> >> > >>>>> than what we've already said. We might only introduce additional
> >> > >>>>> clarification into the XML Syntax document about relative URIs: we might
> >> > >>>>> say that if you want to store such URIs, then you should explicitly turn
> >> > >>>>> xml:base off on the element whether you are doing so; otherwise, your
> >> > >>>>> relative URIs will accidentally be resolved against the xml:base and
> >> > >>>>> that wopuld lead to problems. You can turn this resolution off by
> >> > >>>>> placing on the element an xml:base with some opaque URI.
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> Regards,
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>             Boris
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> ------------------------------------------------------------------------
> >> > >>>>>
> >> > >>>>> *From:* public-owl-wg-request@w3.org
> >> > >>>>> [mailto:public-owl-wg-request@w3.org] *On Behalf Of *Alan Ruttenberg
> >> > >>>>> *Sent:* 24 November 2008 06:05
> >> > >>>>> *To:* W3C OWL Working Group
> >> > >>>>> *Subject:* relative uri references
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> Do we not  have to say how these are resolved in the functional and
> >> > >>>>> manchester syntax, and might it not be best to explicitly say so for all
> >> > >>>>> syntaxes?
> >> > >>>>>
> >> > >>>>>
> >> > >>>>>
> >> > >>>>> -Alan
> >> > >>>>>
> >> > >>>> --
> >> > >>>>
> >> > >>>> Ivan Herman, W3C Semantic Web Activity Lead
> >> > >>>> Home: http://www.w3.org/People/Ivan/
> >> > >>>> PGP Key: http://www.ivan-herman.net/pgpkey.html
> >> > >>>> FOAF: http://www.ivan-herman.net/foaf.rdf
> >> > >>>
> >> > >> --
> >> > >>
> >> > >> Ivan Herman, W3C Semantic Web Activity Lead
> >> > >> Home: http://www.w3.org/People/Ivan/
> >> > >> PGP Key: http://www.ivan-herman.net/pgpkey.html
> >> > >> FOAF: http://www.ivan-herman.net/foaf.rdf
> >> > >
> >> >
> >> > --
> >> >
> >> > Ivan Herman, W3C Semantic Web Activity Lead
> >> > Home: http://www.w3.org/People/Ivan/
> >> > PGP Key: http://www.ivan-herman.net/pgpkey.html
> >> > FOAF: http://www.ivan-herman.net/foaf.rdf
> >
> >

Received on Monday, 24 November 2008 16:37:27 UTC