see also http://groups.google.com/group/metalink-discussion/browse_thread/thread/566c588f85ed5b32/9d427439d57a3d4d
(note: this covered metalink 3, not the current version/RFC) On Tue, Sep 28, 2010 at 1:40 AM, Ivan Shmakov <[email protected]> wrote: > RDF increasingly becomes the preferred model for metadata on the > Web. It thus provoked me to do a bit of research into the RDF > and RDF/XML compatibility of the Metalink XML format. > > Regarding the previous discussion of using RDF (and Dublin Core) > I was able to locate [1], my understanding is that the point > isn't about making Metalink XML compatible with RDF/XML, but > rather about defining a mapping, which can be used to “import” > Metalink metadata into RDF-based models. > > As shown below, the most valuable elements of Metalink XML > cannot be parsed with an RDF/XML parser, which is somewhat > unfortunate. > > Dublin Core is less of a problem. Apparently, the “best current > practice” for an RDF-based representation is to define its own > vocabulary of predicates, while also specifying how these > predicates relate to the similar ones in other vocabularies, > including Dublin Core. Such relations may be described in OWL. > > Now, into the technicalities… > > The subsection 2.13 of the RDF/XML specification [2] reads: > > It is common for RDF graphs to have rdf:type predicates from subject > nodes. These are conventionally called typed nodes in the graph, or > typed node elements in the RDF/XML. RDF/XML allows this triple to > be expressed more concisely. by replacing the rdf:Description node > element name with the namespaced-element corresponding to the RDF > URI reference of the value of the type relationship. There may, of > course, be multiple rdf:type predicates but only one can be used in > this way, the others must remain as property elements or property > attributes. > > This way, some Metalink documents may be read as RDF/XML > documents, provided that the following two superficial changes > are made: > > • the top-level ‘metalink’ element be replaced with ‘rdf:RDF’; > > • all the attributes are given namespace prefixes. > > Consider, e. g.: > > $ cat < example.metalink > <?xml version="1.0" ?> > <rdf:RDF > xmlns="urn:ietf:params:xml:ns:metalink" > xmlns:mtl="urn:ietf:params:xml:ns:metalink" > xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#";> > <file mtl:name="example.ext"> > <size>14471447</size> > <url>ftp://ftp.example.com/example.ext</url> > <url>http://example.com/example.ext</url> > </file> > </rdf:RDF> > $ rdfproc example-metalink \ > parse example.metalink rdfxml > rdfproc: Parsing URI file:... with rdfxml parser > $ rdfproc example-metalink \ > serialize turtle > @prefix rdf: <http://www.w3.org/1999/02/22-rdf-syntax-ns#> . > > [] > a <urn:ietf:params:xml:ns:metalinkfile> ; > <urn:ietf:params:xml:ns:metalinkname> "example.ext" ; > <urn:ietf:params:xml:ns:metalinksize> "14471447" ; > <urn:ietf:params:xml:ns:metalinkurl> "ftp://ftp.example.com/example.ext";, > "http://example.com/example.ext"; . > $ > > Note, however, that (apart from the changes shown above) RDF/XML > representation is incompatible with Metalink in that the > “objects” (RDF graph “nodes”) must be interspersed with > “properties” (RDF “arcs”), which is incompatible with, e. g.: > > <file ...> > ... > <metaurl > mtl:mediatype="torrent" > >http://example.com/example.ext.torrent</metaurl> > ... > </file> > > There, the ‘metaurl’ element is directly contained within > ‘file’, and thus is considered a “proprety” by the RDF/XML > parser, while it should be a “node” in order to contain the > ‘mtl:mediatype’ attribute (which would then be considered a > property by RDF/XML.) > > Unfortunately, most of the valuable elements of Metalink are > specified as both having attributes, and being direct > descendants of the ‘file’ element, which makes them incompatible > with RDF/XML. In particular, these are: ‘metalink:pieces’, > ‘metalink:hash’, ‘metalink:metaurl’, ‘metalink:origin’, > ‘metalink:publisher’, ‘metalink:signature’, ‘metalink:url’. > > While this particular issue could be solved by providing a > separate Metalink XML parser to the RDF tool in question (or by > providing an XSLT transformation), it isn't clear as to whether > the elements above should name (typed) RDF nodes or arcs (or > both?) > > [1] http://article.gmane.org/gmane.comp.web.metalink.devel/318 > [2] http://www.w3.org/TR/REC-rdf-syntax/#section-Syntax-typed-nodes > > -- > FSF associate member #7257 > -- (( Anthony Bryan ... Metalink [ http://www.metalinker.org ] )) Easier, More Reliable, Self Healing Downloads -- You received this message because you are subscribed to the Google Groups "Metalink Discussion" group. To post to this group, send email to [email protected]. To unsubscribe from this group, send email to [email protected]. For more options, visit this group at http://groups.google.com/group/metalink-discussion?hl=en.
