Doubts about RDF

4

418928

Hi everybody,

I have some doubts about RDF. I hope you can help me with them:

-In http://www.w3.org/TR/rdf-primer, they use the namespace
"http://www.example.org/terms/">", but the URL "http://
www.example.org"
does not exist, so it doesn't define any terms. Is this out-of-date?

-Difference between rdf:about and rdf:ID. Can I use only rdf:about?
Can I
use only rdf:ID?

-The RDF graph data model is the same in any collection (e.g., using
"Alt"
or "Bag" or "Seq"). How is this possible? It seems it does not make
sense
that the data model is the same...

-When we say something like:

<rdf:Statement rdf:about="#triple12345">

how should I build the entire URI (#triple12345). Is it relative to
the
current document? Can I omit the "#"?

-Can multiple inheritance be used regarding properties (besides
classes)?

-Why some of the elements in RDFS are defined with the namespace "rdf"
and
others with "rdfs"? For example, "rdf:Bag" and "rdfs:Container" or
"rdfs:subclassOf". I would expect all of them defined with "rdfs"
(otherwise, it seems they are part of RDF, although they appear in the
RDFS description). Can anybody clarify me this confusion?

-In the RDF Primer (http://www.w3.org/TR/rdf-primer/, Example 26),
there
are two lines:

<rdfs:range rdf:resource="&xsd;integer"/>

<rdfs:Datatype rdf:about="&xsd;integer"/>

My question is: is the second line needed? What does it mean? For me,
it
makes no sense, as "&xsd;integer" is a standard datatype.

-In the example 29 of that same document, it defines a
xml:base="http://example.org/things". Despite the explanation below, I
don't understand what does this mean or what is the purpose of this. I
think the xml:base could be removed. Any idea?

-In that same example, they clarify that "the range declaration does
not
automatically assign a datatype to a plain literal, and so a typed
literal
of the appropriate datatype must be explicitly provided". I was
wondering
why the datatype should not be assigned implicitly. Is there any
reason
for having to do the user by himself/herself?

-I think I read somewhere the definition of RDF using RDF itself. But
I
cannot find it now... Can anybody please point me to the place where I
can
find this?

-How is the state of the art in query languages for RDF? Is RQL the
best?
RDQL? Any other?

-If I want to specify a URI that points to a local document. How can I
do
it? If I indicate that a class is subclass of another class that is
defined in a document whose URI is a URL, every time that a reasoner
uses
this information, does it have to access the URL to check the
superclass
definition? Or does it cache the remote document?

-I have read that RDF cannot prevent contradictions, although a
reasoner
could detect them. What does this mean? I far as I know, if the
reasoner
can detect it, that's fine. What more could we get? Does OWL provide
something better in this regard?

Thanks a lot in advance,

Sergio
 
M

Malcolm Dew-Jones

(e-mail address removed) ([email protected]) wrote:
: Hi everybody,

: I have some doubts about RDF. I hope you can help me with them:

: -In http://www.w3.org/TR/rdf-primer, they use the namespace
: "http://www.example.org/terms/">", but the URL "http://
: www.example.org"
: does not exist, so it doesn't define any terms. Is this out-of-date?

A name space is not a web site, it has no need to exist. It is just a
string used as a name in an xml file. Now ask yourself, What if you
wanted to combine two xml files created by two different authors that both
used the same name for different things? That would be inconvenient - it
is very useful if different authors can guarantee they always use
different names. The best way to ensure different authors use different
names is for each author to include their own domain name as part of the
name. If every author does that then every name will always be unique,
since noone else will ever use the same name.
 

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