Doubts about RDF

Discussion in 'XML' started by 418928@cepsz.unizar.es, May 7, 2007.

  1. Guest

    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 Is this out-of-date?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
    , May 7, 2007
    #1
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  2. () 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.
    Malcolm Dew-Jones, May 9, 2007
    #2
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