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Re: [SWC] comments/review SWC - replies to Jos' replies on part 1 of the review.

From: Axel Polleres <axel.polleres@deri.org>
Date: Mon, 30 Jun 2008 15:31:52 +0100
Message-ID: <4868EE58.7020300@deri.org>
To: Jos de Bruijn <debruijn@inf.unibz.it>
CC: RIF WG <public-rif-wg@w3.org>

Jos de Bruijn wrote:
> 
> Axel,
> 
> Thanks a lot for the detailed review.  I implemented all your 
> suggestions, with the exception of the ones mentioned below.
> 
> 
>> *) "A typical scenario for the use of RIF with RDF/OWL is the
>> exchange of rules that either use RDF data or an RDFS or OWL
>> ontology" -> "A typical scenario for the use of RIF with RDF/OWL is
>> the exchange of rules that use RDF data possibly along with some
>> RDFS or OWL ontologies"
> 
> Your suggested wording seems to require the use of RDF data when using 
> RDFS or OWL ontologies.  Instead, I changed the first or to "and/or":
> "RDF data and/or RDFS or OWL ontologies"
> 
>>
>> *) "The notation of certain symbols particularly IRI's and plain
>> literals is slighlty different from the noation in RDF/OWL. This
>> diference is illustrated in Section [...]." --> "The notation of
>> certain symbols particularly IRI's and plain literals is slighlty
>> different from the noation in RDF/OWL. These differences is
>> illustrated in Section [...]."
> 
> Done.
> 
>>
>> Do we need this at all? do we need section 2 at all? the latest PS
>> reconciles most of the differences, and section 2 has some flaws
>> anyway, see later comments below.
> 
> We need a section to explain the differences.  Even if the shortcut 
> syntax looks the same for some cases, the syntax is still different, as 
> illustrated, for example, at the end of section 3.2.1.2.
> 
>>
>> *) "The Appendix [...] describes how reasoning with combinations of
>> RIF rules with RDF and a sub set of OWL DL can be reduced to
>> reasoning with RIF documents."
>>
>> If this is a particular fragment of OWL 2 which we can *name*, then
>> this should be mentioned, or another Editor's note should be added.
> 
> 
> We are *not* concerned with OWL 2; we are concerned with OWL.
> 
>>
>> *) "If the interchange partner B does not have an RDF/OWL aware rule
>> system,but B can process RIF rules[...]" --> "If the interchange
>> partner B does not have an RDF/OWL aware rule system,but B can
>> process RIF BLD rules[...]"
> 
> At the end of the second paragraph in the overview I state "In the 
> remainder, RIF is understood to refer to RIF BLD".  I think that is a 
> sufficient explanation; I think it would be a bad idea to change all 
> mentions of RIF to RIF BLD .
> 
>>
>> *) "All RIF statements are written using the RIF presentation syntax
>> (RIF-BLD). Where possible, this document uses the shortcut syntax for
>> IRIs and strings as defined in (RIF-DTB)." It was descided that the
>> shortcut notation will be copied to BLD, so probably no need to
>> cross-reference DTB here.
> 
> Wake me up when this happens...
> In the meantime I included an editor's note saying that the reference 
> might change.
> 
>> BTW, section 2 seems to duplicate some od
>> this stuff anyway.
 >
> This text in the overview is about notational conventions used in the 
> document.  Section 2 is just some explanation of the differences between 
> the RDF/OWL syntax and the RIF syntax.  Where is the duplication exactly?

I suggest to add a fifth column the table in Section 2 then which shows 
the corresponding RIF shortcuts in RIF's presentation syntax, to 
illustrate that RIF allows shortcuts very similar looking to the RDF 
symbols.

>> *) "[...] compact IRIs prefix:localname or typed literals
>> "literal"^^datatype-IRI." "[...] compact IRIs prefix:localname or
>> typed literals "literal"^^<datatype-IRI>."
> 
> Isn't it also allowed to write compacts IRIs as datatype identifiers? 
> The previous sentence already says how IRIs may be written; so it should 
> be clear that they are either delimited by angle brackets or they are 
> written as compact IRIs.
> 
>>
>> Section 2 : Symbols in RIF vs RDF/OWL (Informative) 
>> ---------------------------------------
>>
>> *) "Unicode sequences with symbol space IRIs (DTB)." --> "Unicode
>> sequences  with IRIs denoting their symbol spaces (DTB)."
> 
> I am reluctant to make this change, because I use the same wording in 
> several places in this paragraph.

You can help yourself by saying somewhere that you speak about symbol 
space IRI when meaning the IRI denoting a symbol space.

>>
>> *) possible problem: In simple RDF there is not entailment for plain
>> literals to literals of type xsd:string, but in your treatment you
>> seem to treat both synonymously, 
> 
> Indeed, they are simply the same.  That they have a different syntax in 
> RDF is simply a bug (or a feature, depending on how you look at it).
> 
>> isn't that a problem for simple RDF
>> entailment?
> 
> If you want to support RIF you have to support data types.  So if you 
> want to combine your RDF data with RIF rules you have to support data 
> types.  What's the problem?

For instance, that with a RIF-implementation that implements the 
embedding, you cannot check simple RDF entailment? I think the subtle 
difference with plain literals and string typed literals probably 
doesn't make a difference normally, but at least, a clarifying remark 
pointing this out would be in order, I think!

>> I used xsd:  as the prefix
>> throughout DTB, I suggest to stick with this and not use xs:
> 
> I guess I did not catch that in DTB. You should actually not use the xsd 
> prefix, but rather the xs prefix.
> The xsd prefix is conventionally associated with the namespace 
> http://www.w3.org/2001/XMLSchema-datatypes#, which is deprecated.
> The xs prefix is conventionally associated with the namespace 
> http://www.w3.org/2001/XMLSchema#, which is the one we use.

ok, we fixed that to xs: for all.

>> *) I find several things confusing in Table 1. All this should be
>> clear from the explanation of shortcuts in DTB/BLD, no need to
>> duplicate here.
> 
> There *is* a need for duplication here, because this section is meant to 
> explain the syntax for RIF symbols to the semantic Web crowd who may not 
> have read DTB or BLD.

fine, but see above, I suggest to add another column.

>>  I find this table more confusing than enlighning.
>> E.g. -  "IRI" is used instead of "constant in the <tt>rif:iri</tt>
>> symbol space -  "String" is used instead of "constant in the
>> <tt>xs:string</tt> symbol space - "Symbol in  symbol space" looks
>> strange. - 
> 
>> we need to mention then that our
>> entailment is strictly speaking doing more than simple RDF
>> entailment.
> 
> There is already an example at the end of section 3.2.1.2.  Do you think 
> we need more?

The additional example I'd put is that

  a b "c".

implies, in a RIF-RDF combination

  a b "c"^^xs:string.

and vice versa, because this not obvious for RDF people, I guess.


>> Section 3: RDF Compatibility ---------------------
>>
>>
>> *) "conclusions that may be drawn from the RIF rules are reflected in
>> the RDF graphs" -> "conclusions that may be drawn from RIF rules are
>> reflected in the RDF graphs"
> 
> In that case, I guess the article in front of RDF graphs would also have 
> to be removed.
> I actually think we should keep the articles, because we are referring 
> to rules and graphs in a particular combination.
> 
>>
>> *) "there is  a corresponcence between RDF triples of the form s p o
>> and RIF frame formulas of the form s[p->o]" -> "there is  a
>> corresponcence between ground (i.e., blank node free) RDF triples of
>> the form s p o and RIF frame formulas of the form s[p->o]"
> 
> This seems to excludes the use of blank nodes and of variables.  I don't 
> think we want to do that.

So, how does an RDF triple with  blank nodes have a correspondence?
I mean: the correspondence with bnodes is not obvious and defined in 
this document (sometimes you replace bnodes by variables sometimes by 
sk... so s p o does NOT correspond to s[p->o] for triples with bnodes) 
whereas for ground triples it is.

>> *) in the example: why use john, jack and mary and not the good old
>> alice bob and charles everybody is familiar with? ;-)
> 
> John, Jack, and Mary are much nicer people :-)

Well, that almost sounds like Johnny, Jim and Jack... cheers.
and other specs from the RDF realm already use alice, bob, just seems 
more coherent.

>> *) I find the "nameBearer" example a bit too artificial ... personal
>> taste... what about "namedObject" instead?
> 
> John is not an object, but a person. how about "named"?

A person is also an object, so what?
"named" is a strange class name, isn't it?

>> *) "The syntax of the names in these sets [...]" -> "an abstract
>> syntax for the names in these sets [...]"
>
> Isn't there just one abstract syntax? 

There are more than one syntaxes, e.g. the RDF/XML syntax.

>  Besides, the reader might not be 
> familiar with the term "abstract syntax", so I'm rather hesitant to make 
> this change.

I would still suggest it strongly, because this is not THE syntax.

>>
>> *) My only worry about "generalized RDF graphs is: Does this imply
>> that RIF compliant implementations need to support generalized
>> graphs?
> 
> No
> First of all, there is no notion of compliance defined for RIF-RDF 
> combinations.
> Second, if one does not encounter generalized RDF graphs, one does not 
> need to support them.
> Third, if you already support RIF-RDF combinations with standard RDF 
> graphs, then dealing with generalized RDF graphs is easy (nearly trivial).
> 
>> As mentioned in earlier discussions I think there is reasons
>> NOT to assume the generalization for bnodes in pred positions in
>> future versions of RDF.
> 
> If there are no RDF graphs with blank nodes in predicates positions, you 
> do not have to deal with them.
> Note also that one of the editors of the RDF concepts document is 
> strongly in favor of generalized RDF graphs [1].
> 
> [1] 
> http://lists.w3.org/Archives/Public/public-rif-comments/2008May/0003.html 
> (comment A)
> 
> 
>> *) I consistently changed "datatype" to "data type" in DTB, we should
>> b e consistent over all documents.
> 
> I tried to be consistent and chose "datatype", as in the XML schema 
> datatypes specification, as well as the RDF and OWL specification 
> documents.
> It would indeed be good to be consistent in all documents and change 
> "data type" to "datatype".

not sure, what does the group think? the change only rquires a couple of 
minutes, but I want to have some 3rd party opinions here.

>> *) "conforming datatype map" ... conforming to what? maybe better use
>> something like "well-defined datatype map"
> 
> "Conforming" may not be the best term, but I could not think of anything 
> better.

It is weird. Something that "conforms" conforms to *something*, so what 
is this something here?

> I would argue that any partial mapping from IRIs to datatypes is 
> a well-defined datatype map.

you can define the term "well-defined".


>> *) "The notion of well-typed literal loosely correspond with the
>> notion of legal symbol in RIF" -> "The notion of well-typed literal
>> loosely corresponds to the notion of legal symbol in RIF" - is there
>> a link reference here to "legal symbol"? (can't see in my pdf print) - 
>> I don't like "loosely coresponds", this doesn't say anything.
> 
> I removed the reference to "legal symbol", because you said you had no 
> intention of defining it in DTB.
> 
>>
>>
>> Section 3.2 =======
>>
>> *) I do not understand your rationale on capitalizing or
>> non-capitalizing rdf and rdfs. In my opinion, you should use RDF and
>> RDFS in capital letter anywhere. rdf/rdfs looks awkward.
> 
> I do not capitalize semantic concepts, following the RDF semantics 
> specification.
> 

It is weird already there.

>> Section 3.2.1 ========
>>
>> *) "correspondence between RDF triples of the form s p o and RIF
>> frames ... (cf. Table 1)" "correspondence between ground RDF triples
>> of the form s p o and RIF frames ." - Table 1 doesn't cover bnodes!
>>
> 
> If we want to be very precise here, we need a lot of additional text to 
> cover the case of variables.  I would prefer to keep the more general 
> statement that's there now.

see above. the bnodes make a big differnce. there are no variables in 
RDF graphs (except bnodes)... so, what's the problem with this slight 
rewording which is much clearer?

>>
>> *) possible problem/remark: OWL/RDF data or knowledge bases by no
>> means restrict the usage of RIF reserved identifiers or built-ins  as
>> identifiers for arbitrary resources in RDF triples or as OWL classes
>> etc. Is this a possible problem which we should make a remark over?
> 
> I don't see a problem.
> 
>> e.g. that we ignore triples using the "RIF vocabulary" (to be
>> defined.)
> 
> We certainly do not ignore such triples , and in some cases the use of 
> RIF vocabulary has semantic consequences (e.g., the example at the end 
> of section 3.2.1.2).
> 
> I do not think further remarks are necessary.
> 
>>
>> *) "frame is a mapping from Dind to functions of the form
>> SetOfFiniteBags(Dind  Dind) ? D,"
>>
>> I am not sure wether I understand this. E.g. rdf:type, are not
>> finite... so what does this setoffinitebags mean?
> 
> The bag is necessary for interpreting frames consisting of one object 
> with multiple properties.  The set (of bags) may be infinite.
> this comes from the BLD specification.

yes, it is hard to grasp. well...

>> *) "considered datatypes" ... I am a bit worried about these pointers
>> to dtb. Actually, you definition of required RIF datatype points to
>> the required *symbol spaces* definition in DTB
>>
>> Did you add the respective anchor <span id="def-required-datatypes"
>> class="anchor"> in the DTB document? this anchor is confusing, since
>> the list defines symbol spaces, not data types.
> 
> The anchor was in the wrong location.  I moved it to the definition in 
> section 2.2.
> 
>>
>> Section 3.2.1.2: ==========
>>
>> *) In ther first definition, I miss a bullet point for plain
>> literals, 6. only seems to cover typed literals.
> 
> The interpretation of plan literals in RDF interpretations is fixed. So, 
> we don't need a condition here.
> 
>>
>>
>> Section 3.2.2: =========
>>
>> *) You use  "a" = "b" as an inconsistency... 
> 
> I'm not "using" this statement.  There is merely an example putting 
> something out.

well, that's nitpicking...  you use it for inconsistency, yes?

>> Don' we again have
>> problems in simple entailment, if we treat plain literals
>> synonymously with xsd:strings? In simple RDF interpretations
>> "a"^^xsd:string = "b"^^xsd:string wouldn't be an inconsistency,
>> right?
> 
> Again, I don't see what the problem is.

the problem is: by

"a"^^xsd:string = "b"^^xsd:string

You imply that this is interpreted as an inconsistency.
In simple RDF such an equality is not an inconsistency.
Anyway, If you add the clarifying remark I talked about before, you can 
simply reference it here again and just point out that the reader shall 
be aware of this treatment in RIF. Just wanted a pointer, because I 
think it is not obvious.

>> Section 5: ======
>>
>> *) "Here, ti is an IRI constant of the form <absolute-IRI>, where
>> absolute-IRI is the location of an RDF graph to be imported, and pi
>> is an IRI constant denoting the profile to be used."
>>
>> - by "location" you mean web-accessible? 
> 
> Not necessarily.  It may also be the location on the local file system, 
> for example.
> You may even print a book consisting of an RDF graph, in which case you 
> would could the ISBN-IRI :-)
> 
>> or named graphs a la Carrol?
> 
> I don't know what those are.  Is there a standard about them?

Here some maybe useful paragraph from the SPARQL spec on that for 
explainin the maening of the FROM NAMED clause, maybe we can reuse this 
analogously:

"The FROM NAMED syntax suggests that the IRI identifies the 
corresponding graph, but the relationship between an IRI and a graph in 
an RDF dataset is indirect. The IRI identifies a resource, and the 
resource is represented by a graph (or, more precisely: by a document 
that serializes a graph). For further details see [WEBARCH]."

Would need to check in which sense this is clarified in WEBARCH

[WEBARCH]
     Architecture of the World Wide Web, Volume One, I. Jacobs, N. 
Walsh, Editors, W3C Recommendation, 15 December 2004, 
http://www.w3.org/TR/2004/REC-webarch-20041215/ . Latest version is 
available at http://www.w3.org/TR/webarch/ .

>> maybe needs clarification 
> 
> I thought to use of IRIs to denote locations, especially locations on 
> the Web, is quite obvious to a Web audience.

If other specs think it is necessary to clarify this with a remark like 
the above, we are maybe also better off to follow this practice.

>> - it would be worthwhile to
>> forward-reference to the predifined list of profiles in this document
>> in section 5.1 here. Otherwise, I am a bit lost what a profile IRI
>> actuall is.
> 
> There is a mention of profile in the first paragraph.  If anything 
> should be further explained, it should be done there.  Do you think any 
> change is necessary?

yes: add a forward reference to the predifined list of profiles in this 
document in section 5.1 here.

>>
>> *) "In case several graphs are imported in a document, and these
>> imports specify different profile, the highest of these profiles is
>> used."
>>
>> - At this point the reader has no idea that there is actually an
>> order among profiles, so the meaning of "highest" is unclear... again
>> a remark/forward-reference would be worthwhile for clarification.
> 
> I added the text "Profiles are assumed to be ordered.".  Do you think 
> this is sufficient?

Profiles are assumed to be ordered (see ... below).

>> *) to the best of his ability - > to the best of its ability
> 
> I'm not so sure about this; "its" seems rather impersonal.
> you have some native speakers around in your office in Galway.  Address 
> them what they think?

"his" is not gender neutral, I suggest 'its' or 'her/his', I don;t need 
a native speaker for making this suggestion which is purely driven by 
concerns about political correctness. ;-)

>> *) The sentence: "Any profile that is used with RIF must specify an
>> IRI that identifies it and notions of model, satisfiability, and
>> entailment for combinations." seems to contradict the notion of the
>> "generic" profile, probably you want to weaken or drop this
>> statement. e.g. "Any non-<tt>generic</tt> profile [...]"
> 
> I do not think others should specify generic profiles. 

Fine, it is just not clear from your current wording.

>  There is already one generic profile and one should choose 
> this whenever one needs a  generic profile.

That's why I say you should reformulate the sentence to
  "Any non-<tt>generic</tt> profile [...]"
then there is no problem, because the sentence doesn't hold for the 
<tt>generic</tt> profile.

>> *) Final remark: I have some worries about the following: What if/How
>> can someone define profile orders for new profiles, particularly, how
>> does someone define profiles which are in a "<" relation with
>> existing profiles defined in this document? I.e., what is rthe
>> intended semantics of "<"? does it mean "monotonicity of (ground?)
>> entailments" or something else?
> 
> it does not have an intended semantics.

ah. ... well.

>> I think this should be defined
>> somehow. Otherwise, some third party could define a complete nonsense
>> order of profiles.
> 
> People can always do nonsensical things, whatever constraints you can 
> think of.
> I do not really the need for defining further restrictions.

Any other opinions? Anybody else read so far? :-)

>> Section 7: Appendix =============
>>
>> *) "RIF-RDF combinations can be embedded into RIF Documents in a
>> fairly straightforward way, thereby demonstrating how a RIF-compliant
>> translator without native support for RDF can process RIF-RDF
>> combinations." --> "RIF-RDF combinations can be embedded into RIF
>> Documents which enables RIF-compliant translators without native
>> support for RDF to process RIF-RDF combinations."
> 
> I like my text better, because the appendix shows just one possible 
> embedding, so it is a demonstration of how it can be done, not an 
> enabling technology.

I tried to suggest you a more crisp and readable wording.

>> *) "The embeddings are defined using the embedding function tr," make
>> tr italic.
> 
> I already use italicizing for meta-variables, so I don't think it is a 
> good thing to italicize tr.

It looks weird if you use the same font as floating text.

>> BTW: maybe you should simply move this to the overview and also
>> introduce the func: and pred: prefixes there.
> 
> I deliberately did not include them in the overview, because they are 
> not used anywhere else (besides the appendix) in the document.

Doesn't matter. I still suggest this, these prefixes hold for all RIF 
documents.

>> Section 7.1 =======
>>
>> *) "The embedding of RIF-RDF combinations is not defined for
>> combinations that include infinite RDF graphs and for combinations
>> that include RDF graphs with RDF URI references that are not absolute
>> IRIs."
>>
>> Why are relative IRIs a problem? can be resolved anyway, or no?
> 
> I'm not talking about relative IRIs.  I'm talking about the RDF URI 
> references that are not IRIs.

Can you give me an example? ...

> Relative IRIs are merely a surface syntax issue; the definition of 
> combinations is on the abstract syntax level, and there all IRIs are 
> absolute.
> 
>> probably, a reference to the respective section on relative/absolute
>> IRIs in BLD is in order.
> 
> I included a reference to the endnote explaining the issue

... ah, ok, now I got you, you say that RDF is more liberal than rfc3987.

>> Section 7.1.1 ========
>>
>> *) I am worried about row 3 in the table... i.e. the translation of
>> plain literals into xsd:string constants, as I think this can be
>> problematic with respect to simple entailment.
> 
> Your concern is a semantics issue, not an issue for this appendix

:-) yes, it is the same concern as expressed already several times 
above. If we have the generic remark that clarifies the slight semantic 
difference between rdf entailment and rif-rdf entailment, I am fine.

>> *) in the last row of the table: "Local constant s^^u' that is not
>> used in C" What is u'?
> 
> s^^u' is obtained from "s"^^u.

How? That is weird.

You write now:
"Local constant s^^u' obtained from "s"^^u that is not used in C"

this is still not understandable. I would make an alternative 
suggestion, it I understood it!


>> *) "tr("s"^^u) = "s^^u'"^^rif:local" Unfortunately,  "s^^u'" is not
>> possible in the lexical space of rif:local: From DTB (this was
>> basically discussed at the f2f in galway): "The lexical space of
>> rif:local is a subspace of the lexical space of xsd:string. Namely,
>> we allow unicode strings which are also valid XML NCNames as defined
>> in [XML-NS]."
> 
> As discussed (and no also changed in DTB) "The lexical space of 
> rif:local is the same as the lexical space of xsd:string, i.e. all 
> Unicode strings."

right, this is done.

>> Section 7.1.2 ========
>>
>> *) write the function "sk" in italic.
> 
> As for tr, I am reluctant to italicize functions.

you might be reluctant, it still looks odd in the text.
3rd arty opinions would be good, but again let's see who else reads that 
far. :-)

>> *) "and variables are Skolemized, i.e., replaced with constant
>> symbols" -> "and variables are Skolemized, i.e., replaced with
>> "fresh" constant symbols"
>>
>> This is not full Skolemization, maybe you should write rather
>> "replaced with fresh constants, similar to Skolemization."
> 
> why is it not full Skolemization?

becaus skolemization introduces skolem-*functions* (not necessarily only 
constants)

>> This constant-only-Skolemization only works for a RIF representation
>> of an RDF graph, 
> 
> Yes
>>
>> *) In the last row of the translation table: It seems to me that
>> variable names and bnodes need to be standarized apart as a
> 
> What does "standarized apart" mean?

that blank nodes labels are disambiguated beforehand:
http://www.w3.org/TR/rdf-mt/

"A merge of a set of RDF graphs is defined as follows. If the graphs in 
the set have no blank nodes in common, then the union of the graphs is a 
merge; if they do share blank nodes, then it is the union of a set of 
graphs that is obtained by replacing the graphs in the set by equivalent 
graphs that share no blank nodes. This is often described by saying that 
the blank nodes have been 'standardized apart'. It is easy to see that 
any two merges are equivalent, so we will refer to the merge, following 
the convention on equivalent graphs. Using the convention on equivalent 
graphs and identity, any graph in the original set is considered to be a 
subgraph of the merge."

>> preprocessing step  before in <R,S>, to make this work.
> 
> Is there an error in the embedding?  what is the error precisely?

If you don't disambiguate bnodes before merging the graphs in R, you 
risk unwanted corellations.

>> Section 7.1.3 ========
>>
>> *) "Even though the semantics of the RDF vocabulary does not need to
>> be axiomatized for simple entailment, the connection between RIF
>> class membership and subclass statements and the RDF type and
>> subclass statements needs to be axiomatized."
>>
>> hmmm, something in this sentence is confusing, not sure what...
> 
> Let me know if you find out.  In the meantime I changed the text to
> 
> "The semantics of the RDF vocabulary does not need to be axiomatized for 
> simple entailment.  Nonetheless, the connection between RIF class 
> membership and subclass statements and the RDF type and subclass 
> statements needs  axiomatization."

sounds better :)

>> mayb
>> just cutting it down to: "The connection between RIF class membership
>> and subclass statements and the RDF type and subclass statements
>> needs to be axiomatized." would be fine.
>>
>> *) "by using the embeddings of RDF graphs defined in the previous
>> section." -> "by using the embeddings of RDF graphs defined above." 
>> (the previous section is section 6...)
>>
>> *) General comment on the embedding theorems and proofs:
>>
>> It seems to me that you should rather group.
>>
>> "A RIF-RDF combination <R,{S1,...,Sn}> is satisfiable iff there is a
>> semantic multi-structure I that is a model of merge({R, Rsimple,
>> trR(S1), ..., trR(Sn)}). "
>>
>> and
>>
>> "A RIF-RDF combination C=<R,{S1,...,Sn}> simple-entails a generalized
>> RDF graph T if and only if merge({R, trR(S1), ..., trR(Sn)}) entails
>> trQ(T)."
>>
>> in one theorem, and proof it by the Lemma:
>>
>> "C simple-entails an existentially closed RIF-BLD condition formula ?
>> if and only if merge({R, Rsimple, trR(S1), ..., trR(Sn}) entails ?."
>>
>> That seems more logical than grouping the latter two in a theorem,
>> i.e.: the important (theorem) are the former two, the latter is a
>> lemma from which these two follow. As it looks now, the second
>> theorem says two different things at once, which are not logically
>> related. If you group it the other way around, you can just proof the
>> last one, and the other two follow logically...
> 
> Entailment of condition formulas is certainly just as important as 
> entailment of graphs, especially when considering RDFS/OWL ontologies as 
> data model for the ruleset.
> Thinking a bit about it, it also seems logical to consider both notions 
> of entailment in the same theorem, as there are also defined in the same 
> definition.
> 
> I did move the theorems concerning satisfiability down, below the 
> theorem concerning entailment.

saw that. fine for me.

>> proof: => side:
>>
>> *) In the proof, why doe we need the paragraph "Assume now that R'
>> does not entail trQ(T), [...]" in the end of the => direction at all?
>> It seems that the proof of the => side is complete before, and this
>> paragraph could, especially if you regroup the theorem/lemma as
>> suggested just be mentioned as "a consequence of the lemma".
> 
> It is necessary, because the embedding of non-ground graphs is different 
> between the entailing and the entailed graph.
> 
>>
>> proof: <= side:
>>
>> *) What is I$,
> 
> it is a definition, not a reference.
> 
>> I find the use of the '$' symbol a bit confusing.
>> Couldn't you use I' instead of I$?
> 
> I could not get the "'" to work with the wiki formatting.

did you try <nowiki>'</nowiki> ?

>> *) By the way: I find the ambiguous use of the letter 'C' for C and
>> I_C possibly confusing.
> 
> C is consistently used for combinations, so there will probably not be 
> that much confusion.
> Do you have a better suggestion?

S = <G,R>

insead of

C = <S,R>

maybe?

because then G is a set of *g*raphs, R is a *r*uleset and we use S for 
the combination (I wondered about S for the graph set anyway...)

>> *) Again, the paragraph  "Assume now that C doe not entail ..." seems
>> a bit redundant. Again, regrouping the theorem, and then saying that
>> this is a consequence of the application of the lemma as mentioned
>> above, would make this shorter.
> 
> Again, this is certainly not redundant, because the embedding of the 
> graph is different.
> 
>>
>> Section 7.1.4 ========
>>
> 
>> *) Can't we use pred:isXMLLiteral instead of ex:illxml? If not,
>> shouldn't we define ex:illxml as a predicate in DTB?
> 
> As discussed over the phone, the answer is no in both cases.

I think I would like to have the pred for illxml in DTB... since people 
who want to *implement* rif-rfd, need to implement it anyway... or no?

>> 3) The lemma has a long proof, but you can drop some paragraphs.
> 
> This doesn't help me much.  Which paragraphs can be dropped and why?

Is better now with the new structuring, I guess.

Axel

-- 
Dr. Axel Polleres, Digital Enterprise Research Institute (DERI)
email: axel.polleres@deri.org  url: http://www.polleres.net/

Everything is possible:
rdfs:subClassOf rdfs:subPropertyOf rdfs:Resource.
rdfs:subClassOf rdfs:subPropertyOf rdfs:subPropertyOf.
rdf:type rdfs:subPropertyOf rdfs:subClassOf.
rdfs:subClassOf rdf:type owl:SymmetricProperty.
Received on Monday, 30 June 2008 14:32:40 GMT

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