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Re: RDF Semantics: 11 comments

From: pat hayes <phayes@ai.uwf.edu>
Date: Mon, 24 Feb 2003 09:51:51 -0600
Message-Id: <p05111b47ba7fedf1752d@[]>
To: herman.ter.horst@philips.com
Cc: www-rdf-comments@w3.org, bwm@hplb.hpl.hp.com

(Brian, see end.)

>RDF Semantics document
>Last Call version, 23 January 2003
>Below I give comments to indicate several
>places where a small correction / clarification
>should be made, in my view.
>This list of commentswas mailed earlier to the WebOnt WG [1].

For the record, most of these comments have been accepted as 
editorial changes by the editor and suitable corrections are now in 
the editor's draft.

>Section 0.3, third paragraph, last sentence:
>...to obtain another set S' of graphs which are isomorphic
>to those in S.
>Here 'isomorphic' is not defined: it should be 'equivalent'
>(if this is the term that will be used)


>The same remark applies to a sentence near the end of
>Section 0.3: "By our convention, such isomorphic
>graphs are considered to be identical."

deleted, text re-worded

>1.3 last sentence: "A simple interpretation can be viewed
>as having an empty vocabulary".  This is confusing, as
>the vocabulary of any useful interpretation is not empty.
>Perhaps a term such as "special vocabulary"
>should be more formally introduced, so that the cited
>sentence could speak of an 'empty special vocabulary'.

Sentence deleted

>The next paragraph in Section 1.3 speaks of
>"simple literals", which are not defined.  I guess that
>plain literals is what is meant here.


>Section 2, first paragraph.
>The definition of entailment is given for
>a "set of expressions" S and an (unspecified) E.
>Later, S always stands for a finite set of RDF graphs
>or for one RDF graph and E stands for an RDF graph.
>I believe that the readability would be much improved
>by introducing these intended meanings of S and E
>here already.  Otherwise, the reader needs to match
>the word expression with the word RDF graph, which
>is not directly intuitive.
>It would also help the reader if it is stated here explicitly
>that if S entails E, then the vocabulary of S includes
>that of E.

Changes made as suggested

>Suggestion for clarification in the next paragraph:
>>  Any process which constructs a graph E from some other
>>  graph(s) S is said to be (simply) valid if
>[add] in each case
>>  S entails E, otherwise invalid.
>Without this addition, the meaning is not entirely
>clear, in my view.

changes made

>Section 2.1, second paragraph
>>  Such an internally redundant graph is equivalent to one
>>  of its own instances ...
>Here 'equivalent' is not defined: it is not 'RDF graph
>equivalence' (see other remark).
>What is apparently meant here is that there is
>entailment in both directions.

wording corrected

>Section 3.1, first sentence
>The abbreviation rdfRV is not clear: what does R stand for?
>It seems that this abbreviation could be omitted as it is
>not used elsewhere.
>The more fundamental vocabulary seems to be rdfV,
>introduced later.

True. Text rewritten for clarity.

>Section 3.1, example
>IR = {1,2,T,P} should be replaced by IR = LV union {1,2,T,P}


>Section 3.4, Datatype monotonicity lemma.
>This lemma involves the notion of D-entailment, which
>is not yet defined at this point in the text.
>This seems to need some more explanation, moreover.
>In order to prove the lemma, if the D'-interpretation
>I satisfies S, it needs to be proved that I satisfies
>E.  So it is given that ICEXT((I(rdfs:Datatype))=D'.
>How is it concluded that ICEXT((I(rdfs:Datatype))=D,
>as is needed to conclude that I satisfies E?

Text rewritten and lemma re-stated in a different form to fix this.

>It is clear that the new version of the RDF Semantics
>document depends strongly on the RDF Concepts and
>Abstract Syntax document.
>The Semantics document is the more mathematically oriented
>document, and can be made more self-contained by just
>recalling/including in the beginning of Section 0.2
>the abstract definition of RDF graph:
>given three pairwise disjoint sets U (urirefs), B (blank
>nodes), and L (literals), an RDF graph is a subset of
>U union B  x  U  x  U  union B union L.
>This would clarify the Semantics document very much,
>and diminish strongly the dependence on another 23 page
>document.  Much of the content of the RDF Semantics document
>depends only on this.
>For specific details about urirefs/literals, one needs
>to go to the Concepts document, of course.

This change is possible, but is an action which requires work by 
several editors so is not yet completed.

Brian, can be we have an issue number for this? The issue is, to what 
extent should the various documents attempt to be self-contained in 
giving definitions, etc. (for readability) as opposed to 
cross-referenced (to reduce risk of mismatched definitions) ? Right 
now we have a mixture of policies and it would be better if there was 
a single one to which we could all cleave.


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Received on Monday, 24 February 2003 10:51:43 UTC

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