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From: Peter F. Patel-Schneider (pfps@research.bell-labs.com)
Date: 05/15/02

  • Next message: Dan Connolly: "re: RDF Core working drafts"
    Here are my (initial comments) on the RDF WDs.  I'm willing to collaborate
    with others to jointly come up with a joint response from the joint
    committee.  :-)
    Comments on the Syntax Specification:
    In general the new syntax specification is a giant step forward.  It
    finally makes RDF/XML real XML.  
    I do not understand why the information
    set nodes are transformed into a sequence of events, however.  Why not just
    work directly on the information set nodes.
    Problems and Specific Comments:
    1/ The rule for abbreviation of string-valued properties (Section 2) is not
       correct, because of the XML requirement that attributes names be unique
       within an XML element.
    2/ How is base-uri set from the root node?
    3/ The semantic action for an empty subject on a nodeElement could be
       executed even for element nodes with an rdf:ID or rdf:about attribute.
       This is probably benign, but would cause the blank node identifier
       generator to be pointlessly run resulting in distinct (but
       model-theory-equivalent) sets of n-triples resulting from a single
       RDF/XML document.
    Comments on the Model Theory:
    The model theory makes it very clear that RDF reification is not related in
    any way to reificiation.  This is good, but does raise the issue of why
    reification has been retained.
    The model theory, along with the recent decision allowing multiple rdf:_<n>
    statements in containers for a particular <n>, makes it very clear that
    rdf:Seq is not related to sequences, rdf:bag is not related to bags, and
    rdf:Alt is not related to alternatives.  This is again good, but does raise
    the issue of why these have been retained.
    The theory of literals in the model theory is very weak.  This means that
    there is no relationship whatsoever between literals the differ only on
    their language (or on the presence of a language).
    Comments on the Primer:
    1. Introduction -
    The primer starts 
    	The Resource Description Framework (RDF) is a general-purpose
    	language for representing information in the World Wide Web.
    OK, let's take this at face value.  How can I, in RDF, represent the
    information that right now either it is Tuesday or the sun is shining?
    Well, I can't, of course, because RDF is not a general-purpose language for
    representing information.  Instead RDF is a special-purpose language for
    representing some limited kinds of information.   
    The first example in the primer continues this sort of overstatement.  The
    example contains the RDF statement (in n-triple format)
      <http://www.w3.org/People/EM/contact#me> <personalTitle>
      	"Semantic Web Activity Lead" .
    and claims that this can be read as that there is ``someone who is the
    Semantic Web Activity Lead''.  Well, this is not the reading of this
    n-triple.  A much better reading would be that there is ``someone who's
    personalTitle is "Semantic Web Activity Lead"'', quite a different reading
    The primer mentions ``RDF Schema (and datatypes)'' but there is no treatment of
    datatypes in the primer.
    2. Making Statements About Resources
    This section moves from the very grandiose claims of the Introduction to
    much more defensible descriptions of what RDF can do.  The beginning of
    this section would make a decent introduction section.
    The repeated use of ``a creator whose value is'', and similar constructs,
    are difficult to parse.  As the statement that is being produced here has a
    URI for the creator, it should be possible to just use ``a creator who
    is'', a similarly in several other cases.
    The use of ``temporary identifier'' for blank nodes is wrong and, moreover,
    3. An XML Syntax for RDF
    It is not possible to use namespaces for the URI labels for object nodes,
    except (sometimes) for the labels of types.  In general, only edge labels
    can employ namspaces.  This is illustrated in the example RDF/XML syntax,
    which does not use namespaces for http://www.example.org/index.html.
    The abbreviation example incorrectly states that rdf:resource is (always)
    used when ``the property value is another (existing) resource''.  There
    are, instead, lots of ways to do this in RDF/XML.
    This section retains the notion that rdf:about is used for existing
    resources and rdf:ID is used for new ones.  This is no longer correct, nor
    is it the case that there must be at most one rdf:ID for a given URI in a
    The example for parseType="Resource" misleadingly implies that an rdf:ID
    attribute here would provide a name for the resource.  Instead an rdf:ID
    here is a reification mechanism.
    4. Defining RDF Vocabularies: RDF Schema
    This section give the impression that RDF Schema is nothing more than a
    well-known set of names, to be used in RDF.  Instead RDF Schema is a
    semantic extension to RDF.  This section blurs the distinction between RDF
    and RDF Schema, particularly in its treatment of rdf:type.
    This section is confused about classes.  In one place it states that
    classes are defined as those resources ``whose rdf:type property has a
    valud which is the pre-defined resource rdfs:[C]lass''.  In the next
    paragraph, it states that ``Individual classes [...] will always have an
    rdf:type property whose value is rdfs:Class (or some subclass of rdfs:Class
    5. RDF Containers
    This section dramatically overstates the abilities of RDF containers.  This
    is only partially remedied by the caveats near the end of the section.
    Comments on RDF Schema:
    Overall comments:
    The lack of any treatment of datatyping in RDF (except for a few mentions
    that state that datatyping is deferred to the future) is surprising, and
    disappointing, particularly in light of the mention of XML Schema datatypes
    in the RDF Core WG charter.

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