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Review Mapping to RDF Graphs

From: Markus Krötzsch <mak@aifb.uni-karlsruhe.de>
Date: Tue, 7 Apr 2009 23:38:07 +0200
To: OWL Working Group WG <public-owl-wg@w3.org>
Message-Id: <200904072338.16607.mak@aifb.uni-karlsruhe.de>
Hi Boris, hi Peter,

below are my review comments for the RDF mapping. Overall, I found the 
document sufficiently clear and accessible, even if some minor glitches 
remain. My version was from this morning, so some things may overlap with 
Michael's comments.

Cheers,

Markus



* [Minor] Ontology O maps to RDF graph T(O), but graph G maps to ontology O_G; 
better use a consistent syntax (regarding the position of the parameter O/G)?

* [Editorial] Naming issues: I guess "OWL DL" should now be "OWL 1 DL" (see 
http://www.w3.org/2007/OWL/wiki/Naming).

* [Editorial, minor] "word &mdash; word": AFAIK there are two ways of writing 
dashes correctly in English: "word&mdash;word"
and "word &ndash; word" (or, in LaTeX: "word---word" or "word -- word").

* [Minor] Section 1 and 2: Regarding the style of introducing the meaning of 
entity labels/placeholders:
** Section 1 says "*:x denotes an IRI" but this is not used in Section 2 where 
it says "U denotes an IRI" instead. Other notation of Section 1 (like "_:x") 
is used in Section 2, however. I see that "U" refers to the structural spec 
while "_:x" is RDF syntax; maybe introduce "*:x" only later (i.e. in Sec. 3)?
** Many other labels are used without being introduced, e.g. "ontologyIRI". I 
assume the current policy is to use unintroduced (mnemonic) identifiers 
whenever the meaning of the identifier is clear from the context -- maybe one 
could mention this.

* [Minor] Section 2.1: "if the mapping of a construct refers to the mapping of 
a subconstruct" Maybe it would be clearer to say "if the mapping T(E) of a 
construct E is used in the position of a subject, predicate or object of a 
generated triple".

* [Editorial] Table 1 for "DisjointObjectProperties( OPE1 OPE2 )" uses "op1" 
and "op2" in the second column where "OPE1" and "OPE2" should be used.

* [Minor] The second example in Section 2.2 is actually an example for the 
axiom annotations introduced only in Section 2.3. Up to that point, only 
annotations for ontologies have appeared (in Table 1). Not sure if this is a 
real problem.

* [Bug] Section 3: Generally, it is somewhat unfortunate that "G" is both the 
input graph and the place where remaining triples are stored. The outcome of 
the parsing, e.g., is denoted O_G, but G at the end of the parsing is not the 
same as G at the beginning of the parsing. So when recursively adding content 
to O_G while changing G, the expression O_G is actually different in each 
loop. Similar remarks apply to expressions like Decl(G) and Imp(G). I fear 
that this can only be solved by using another G' (or whatever) for triples 
that still require processing, although this adds more notation to the 
document.

* [Editorial] Section 3: the bullet points say "curly braces { }" but "square 
brackets '[ ]'" -- use single quotes consistently.

* [Bug?] "When a list pattern is matched to G, all variables yi and yj with i 
≠ j MUST be matched to different nodes; furthermore it MUST NOT be possible to 
match the list pattern to two maximal subsets of G such that some variable in 
the first pattern instance is matched to the same node as some (possibly 
different) variable in the second pattern instance." Doesn't this disallow 
multiple lists to have the same (concrete, IRI-named) elements? I guess only 
list bnodes should not be reused, while list members can (but the bnodes are 
the "xi" in this pattern, not the "yi").

* [Bug] Section 3.1.1 state that "the triple  x owl:imports *:y .  is removed 
from G." but also that there is a precondition that "the values for x and *:y 
have not already been considered"  If it can actually occur that a triple is 
found in the parsing for which x and *:y have already been considered, then 
this triple is not removed. Is this intended? But I guess this simply cannot 
occur and the precondition is redundant.

* [Bug] Section 3.1.1: "ontology document accessible from the IRI *:y is 
retrieved [...] The document is parsed into an RDF graph G'." There is some 
confusion of terminology here, I think:
** An "ontology document" according to Syntax must represent an instance of 
Ontology, and hence is never lacking its header.
** Ontology documents may have arbitrary encodings, so to parse them into RDF 
graphs, one would need to apply the mapping T to the extracted ontology 
structure.

But I think "parsing" here really refers to parsing an RDF syntax (only 
RDF/XML syntax?), and the imported non-ontology document must be in some RDF 
syntax for the further steps to be meaningful. Some reference to an RDF spec 
for possible syntaxes and their parsing might be in order.


* [Bug?] Related to the previous note, 3.1.1 also mentions "an owl:imports 
triple pointing to an RDF graph G'"  But the "graph" in RDF seems to be what 
the "ontology" is in OWL, and the property really points to an RDF document.

* [Editorial] In Table 6, row 2, column 3, line 1 there is an additional final 
single quote in "*:x rdf:type owl:ObjectProperty' .'".

* [Minor] Defintion of the set "RIND".
** This notation differs from others such as Imp(G) and Decl(G) where G is 
always included as an argument. Even if it is intended to distinguish RIND 
from Imp() and other notation that appears in Syntax, it should still depend 
on G.
** I did not find the mnemonics of "RIND" very obvious.
** It is somewhat strange that it is emphasised that RIND is initialised to 
the empty set. Should this also be stated for Ind(G) etc. then?

* [Minor] Section 3.2  "This section specifies [...] the set AllDecl(G) of all 
declarations for G"  This sentence is not very clear. This section does not 
say anything more about AllDecl(G), and it certainly does not specify it 
(indeed, it is already required initially in Table 9). Maybe one could have 
two sentences: one saying that the section defines the parsing and the 
resulting ontology, and another one stating that AllDecl(G) is defined as in 
Syntax.

* [Editorial] Section 3.2.1  I think "map an IRI or a blank node x" should be 
"map an IRI or blank node x".

* [Minor] Section 3.2.1  "this is written as CE(x) = ε ..."  Here "this" 
refers to a universal condition over all possible x, while the quoted 
statement refers to only one such x.

* [Editorial] Section 3.2.2: "to each IRI or a blank node x" (remove "a")

* [Bug] Section 3.2.4: According to Syntax, no 0-ary data ranges are possible, 
hence the cases for DataSomeValuesFrom and DataAllValuesFrom in Table 13 
should also require that n >= 1 like it is done in Table 14 (based on Table 14 
I assume that this is not silently assumed for this notation).

* [Bug] Section 3.2.5: A similar remark applies to the last row of Table 18 
(oneOf with at least one member).



-- 
Markus Krötzsch
Institut AIFB, Universität Karlsruhe (TH), 76128 Karlsruhe
phone +49 (0)721 608 7362          fax +49 (0)721 608 5998
mak@aifb.uni-karlsruhe.de          www  http://korrekt.org


Received on Tuesday, 7 April 2009 21:39:02 GMT

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