From: Dan Connolly (connolly@w3.org)
Date: 05/15/02
On Wed, 2002-05-15 at 13:17, Peter F. Patel-Schneider wrote: > Here are my (initial comments) on the RDF WDs. It looks like you went over everything with a fine tooth comb. Thanks! Some quick feedback... > I'm willing to collaborate > with others to jointly come up with a joint response from the joint > committee. :-) > > peter > > > > 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. sounds like a bug, yes. > 2/ How is base-uri set from the root node? It just is, per XML specs. (infoset in particular). > 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. I don't think I understand this; maybe an example would help? > 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. That's a good question. I advocated dropping it altogether. http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jan/0218.html The decision seems to have been made in the 15Feb telcon, with discussion in several previous telcons.... http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Feb/0476.html The chair took an action to add a "fix/drop reification" issue 11Jan http://lists.w3.org/Archives/Public/w3c-rdfcore-wg/2002Jan/0095.html but I don't see it in the issues list. http://www.w3.org/2000/03/rdf-tracking/ So I'd agree that the WG owes a rationale for keeping reification. > 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. Indeed; this issie is currently open. http://www.w3.org/2000/03/rdf-tracking/#rdfms-seq-representation > 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). Hmm... I don't see why it would/should be otherwise. > Comments on the Primer: I presume you mean this version http://www.w3.org/TR/2002/WD-rdf-primer-20020426/ (I haven't read the primer closely...) > 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. yup. > 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 > entirely. agreed. > The primer mentions ``RDF Schema (and datatypes)'' but there is no treatment of > datatypes in the primer. That's a sort of synchronization error; in mid/late Feb, the primer editor was led to believe that datatypes would be merged into RDFS. It didn't work out that way. > 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. Hmm... good point. > 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, > misleading. > > 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. The primer is wrong if it suggest otherwise, indeed. > 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, How so? Are you referring to this text? So far, we've been describing resources that have been defined (and given URIs) already. For instance, in our initial examples, we've been providing descriptive information about example.org's web page, whose URI was http://www.example.org/index.html. We referred to this resource (defined elsewhere) using an rdf:about attribute. However, obviously we also want to be able to define new resources. For example, suppose a company, example.com, wanted to provide an RDF-based catalog of its products as an RDF/XML document, identified by http://www.example.com/2002/04/products. Within that resource, each product might be given a separate RDF description. An example of one of these descriptions (the catalog entry for a tent) might be: 1. <?xml version="1.0"?> 2. <rdf:RDF xmlns:rdf="http://www.w3.org/1999/02/22-rdf-syntax-ns#" 3. xmlns:ex="http://www.example.com/terms/"> [...] I don't see anything incorrect there. rdf:ID can still be used that way. > nor > is it the case that there must be at most one rdf:ID for a given URI in a > document. Yes, it is the case. "Constraint: The names used as values of rdf:ID and rdf:bagID attributes must be unique in a single RDF/XML document..." http://www.w3.org/TR/2002/WD-rdf-syntax-grammar-20020325/#idAttr > 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. Which example? I don't see the problem. > 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. It says that the well-knonwn names don't have related well-known meaning/semantics/axioms? Where? > This section blurs the distinction between RDF > and RDF Schema, particularly in its treatment of rdf:type. Hmm... I haven't read it closely enough to know what you mean by that, I guess. > 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. Yes, it's frustrating that we didn't get a datatyping WD out. -- Dan Connolly, W3C http://www.w3.org/People/Connolly/
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