LC Responses/JR6a

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RDF-based semantics

I have only read a small part of this document. I am concerned about the clarity of the recommendation so my comments are mostly editorial.


Comment on use of DL/Full -- see JR6a


It took me a while to determine that the function of the document is to define what it means for something to be an OWL 2 Full model of an RDF graph. The title and introduction do not help readers to understand this. I suggest a title change, perhaps "OWL 2 Full semantics of RDF graphs", and that the introduction should come out and say something like this.

Going over the first few paragraphs:

  This document defines the RDF-compatible model-theoretic semantics of
  OWL 2, called "OWL 2 Full".

I think what you really mean here is semantics of "RDF graphs". And are you sure that you want "OWL 2 Full" to be the name of a semantics? That seems OK to me, but it's sort of weird. In common use I think it will be taken to mean a language consisting of a combination of syntax (RDF in any of its serializations) and semantics (conditions on interpretation of the OWL 2 vocabulary).

Of course, as a side effect of giving the semantics of graphs, you obtain an alternative semantics for OWL 2 (DL), via the reverse mapping. But that is a separate point.

The semantics given here is the OWL 2

  semantic extension of RDFS [RDF Semantics].

wouldn't it be better to say "OWL 2 Full semantic extension"? It gives a meaning to many graphs not in the image of the reverse mapping (IIUC).

Therefore, the semantic

  meaning

"semantic meaning" is redundant - there is no such thing as a non-semantic meaning. I think you mean one of "meaning", "semantics", "formal meaning", or "formal semantics".

given to an RDF graph by OWL 2 Full includes the meaning given

  to the graph by RDFS. Beyond that, OWL 2 Full gives additional  

meaning

  to all the language features of OWL 2,

By "OWL 2" you mean OWL 2 DL, as defined in the structural specification? A hyperlink to a definition of "OWL 2" would help.

by following the design

  principles that have been applied to the semantics of RDF.
  OWL 2 Full accepts every well-formed RDF graph [RDF] as a
  syntactically valid OWL 2 Full ontology, and gives a precise semantic
  meaning to it.

Instead of "accepts" may I suggest "gives a meaning to". Otherwise one is left wondering what kind of thing OWL 2 Full is that it's able to accept or reject graphs.

I have no idea what an RDF graph that is not well-formed would be. The cited document uses "well-formed" in several different ways, none of which is what I think you mean. Please delete all occurrences of "well-formed" from this document unless you can provide or cite a particular definition.

RDF graphs (which include all OWL 2 Full ontologies) are not syntactic, and therefore cannot be syntactically valid.

Please use "ontology" consistently across all documents. It has a formal meaning defined in the SSFSS document which does not apply to uses in this document. Either change the term used in SSFSS, or change or remove the term used in this document.

You don't exactly define "OWL 2 Full ontology" but I think what you mean is an RDF graph that is intended to be interpreted according to OWL 2 Full. Since "intended" is not operational this seems like a dubious term, and you should consider just saying "RDF graph" instead.

The semantic meaning is determined by the set of OWL 2

  Full semantic conditions, which include and extend all the semantic
  conditions for RDF and RDFS specified in [RDF Semantics].

What is the difference between "include" and "extend"?

See above re "semantic meaning"

OWL 2 Full

  acts as a vocabulary interpretation for the RDF and the RDFS
  vocabularies, and for the OWL 2 Full vocabulary. The OWL 2 Full
  vocabulary is a set of URIs that occur in the sets of RDF triples,
  which define the RDF syntax of OWL 2 [OWL 2 RDF Mapping].

Again I think talking about the "syntax" of an RDF graph is dubious and unnecessary. The OWL 2

  Full semantic conditions specify exactly which triple sets are
  assigned a specific meaning, and what this meaning is.

Why introduce the term "triple set"? I think you're still talking about RDF graphs here.

"the RDFS universe" -- this is not defined anywhere, not even in a cited document. The RDF semantics recommendation is very careful to be "semantically neutral" and only talks about "a universe", not "the universe". The word "the" is distracting (which universe? what's in it, exactly?) and not in accord with my understanding of how model theory is supposed to work.


Section 6.3: The word 'valid' is used but I can't find a definition for it anywhere. By the SSFSS, "ontologies" by definition have a certain amount of validity. If used formally it should be hyperlinked; if used informally I think it is unnecessary and should be deleted. "ontology" is defined formally and should be hyperlinked.

Also in theorem 6.1, I think you mean structural specification, not functional-style syntax, since the reverse mapping produces the former, not the latter.

Dear Jonathan,

Thank you for your message <http://lists.w3.org/Archives/Public/public-owl-comments/2009Jan/0068.html> on one of the OWL 2 Web Ontology Language working drafts.

Some of your comments in the message relate to the use of "OWL 2", "OWL 2 DL", and "OWL 2 Full". These comments are being addressed in another reply. This response addresses only your comments about specific editorial concerns with the RDF-Based Semantics document.

As a general note, please be aware that the RDF-Based Semantics is not yet a Last Call working draft, and it has been considerably edited since the last publication in December. In particular, the two sections you refer to have both changed significantly since then. Several further changes are planned due to your feedback (see below).

In the next release of the document, the first paragraphs of the introduction section are planned to be more clear about the purpose of the document. In particular, it is intended to explicitly state that the document specifies a semantics for arbitrary RDF graphs. The working group does, however, not intend to change the title of the document.

It is intended to not use the name "OWL 2 Full" anymore for the semantics only. Instead, it is planned to consistently refer to the semantics by the term "OWL 2 RDF-Based Semantics".

The text saying that "the semantics given here is the OWL 2 semantic extension of RDFS" is planned to be replaced by other text of a different form, which will hopefully not lead to confusion anymore. You are invited to comment on the new version of the text, when the document is re-published.

Concerning the mentioned redundancy of the word "semantic" in the term "semantic meaning", the working group will leave it to the editor of the document to decide about following your proposed editorial changes.

In the next publication, the introduction is intended to not saying anymore that the semantics "accepts" RDF graphs. Also, in that version the term "well-formed RDF graphs" is intended to be removed. The phrase "include and extend" is also planned to be replaced.

The text talking about "the RDF syntax of OWL 2" is planned to be changed to talk about the "RDF encodings of all OWL 2 language constructs" instead. You are invited to comment on the new version of the text again when the document is re-published.

Section 0.3 of the RDF Semantics specification [RDF Semantics] talks about an RDF graph as a "set of RDF triples", and so does Section 6.2 of the RDF Concepts specification [RDF Concepts]. In the next release of the document, an explicit note on this is planned.

It is intended to not use the term "RDFS universe" in the document anymore. The term "the OWL 2 Full universe" was chosen, because Section 5 of the OWL Semantics and Abstract Syntax specification [OWL 1 SAS] talks about "the OWL universe". However, talking about "the" universe is probably confusing. In the next publication, this is planned to be changed.

Concerning section 6, please note that this section has been in a very preliminary state at the time of the last publication. You are invited to comment on the new version of the section again, when the document is re-published.

[RDF Concepts] <http://www.w3.org/TR/rdf-concepts/> [RDF Semantics] <http://www.w3.org/TR/rdf-mt/> [OWL 1 SAS] <http://www.w3.org/TR/owl-semantics/>

This is a response to a Non-LC comment. If you want to let us know whether or not you are satisfied with the working group's response to your comment, please send your answer to <mailto:public-owl-comments@w3.org> (replying to this email should suffice).

Regards, Michael Schneider on behalf of the W3C OWL Working Group