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[SWC] my review (part I - excl. informative Appendix)

From: Axel Polleres <axel.polleres@deri.org>
Date: Mon, 18 May 2009 00:12:31 +0100
Message-ID: <4A1099DF.7060706@deri.org>
To: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>
attached my review for SWC.

I still need to review the informative Appendix (hopefully  by 
tomorrow), but since I promised to send my review by today, I think it 
is better to split this in two parts.

best,
Axel
-- 
Dr. Axel Polleres
Digital Enterprise Research Institute, National University of Ireland, 
Galway
email: axel.polleres@deri.org  url: http://www.polleres.net/

Section 1:
==========

* "The Rule Interchange Format (RIF) is a format for interchanging
  logical rules over the Web."

remove "locigal" or refer to BLD/FLD only.

* "however, for exchange purposes you assume they are represented
  using RDF graphs. "

you assume->we assume


* "A consumer of the rules retrieves the OWL ontology and translates
  the ontology and document into a combined ontology+rules description
  in its own rule extension of OWL."

It is a bit unfortunate that this import in only unidirectional.
It may be worthewhile (though maybe too late) to ask the OWL WG
whether they would consider a simlar import mechanism on their side
for RIF rules. This way they could e.g. refer to DL-safe RIF rulesets
from OWL ontologies. I didn't check the OWL documents yet, but the
ycould simply accomodate for this by referring to SWC.


* Simple, RDF, RDFS, and Datatype.
 -> Simple, RDF, RDFS, and Datatype entailment.


* "specifying the context of this import,"

shouldn't this be 

"specifying the profile of this import,"

* 
"The following namespace prefixes are used throughout this document:
ex refers to the example namespace http://example.org/example#, xs
refers to the XML schema namespace http://www.w3.org/2001/XMLSchema#,
[...]"

We probably don't want to speak about "the XML schema namespace"
http://www.w3.org/2001/XMLSchema# because only the non-hash version 
of this URI is the actual XML namespace in the sense of XML
Namespaces. If we just change
"refers to the XML Schema namespace"
to
"refers to"
we should be fine. Alternatively, we have to clarify our terminology.


Section 2:
==========

* "2 Symbols in RIF Versus RDF/OWL (Informative)"

I wouldn't capitalize "versus" even in a heading.

Section 3:
==========

* "Note that, even when considering *Simple entailment*"

Optional: Wouldn't it make sense for the convenience of the reader to
link each mention of an entailment relation with its resp. definition in the RDF aand OWL documents?

* 
"For example, the RIF BLD document consisting of the fact
   "a"="b"
"

Note that equality in facts is AT RISK in BLD, and therefore this
example as well. 

* "containing types literals"
--> "containing typed literals"

*
"One consequence of the difference of the alphabets of RDF in RIF"
-->
"One consequence of the difference of the alphabets of RDF and RIF"

*
"These entailments are sanctioned by the semantics of plain literals and xs:strings."
->
"These entailments are sanctioned by the semantics of plain literals and <tt>xs:string</tt>s."

Section 3.1
===========

* Section 3.1.2 
"A RIF-RDF combination consists of a RIF document and zero or more RDF graphs"

Why do we allow only 1 RIF dcoument and arbitrary RDF graphs in a
combination?

* Section 3.1.3.
"Definition. Let T be a set of datatypes."

I suggest to use DTS for sets of datatypes instead of T, compliant with other
defintions speaking aboutsets of datatypes.

Section 3.2
===========

* 3.2.1.1
 
* Section: 3.2.1.3

* "I is a semantic multi-structure [...] "

weren't muli-structures denoted by \hat{I} in BLD/FLD? I suggest in
order to use consistent notation, you use \hat{I} to denote the whole 
multi-structure, whereas you use I to denote the common part only:

"Given a semantic multi-structure \hat{I}={I1, ..., In}, we use the
symbol I to denote the common part of the individual structures I1,
..., In. In the following, we will - slightly simplifying - also refer
to I as a multi-structure, meaning only this common part of \hat{I}."

Would that make sense?


BTW: Why do we need multi-structures, if a combination has always
exactly one RDF graph?


* 
Conditions 4,6,7,8 in the definition in Section 3.2.1.3
enforce some "parts of" D-entailment, i.e. somewhat "D minus RDFS", right? 

E.g. let S1= {{ :s :p "foo" }}, S2= {{ :s :p "foo"^^xs:string }}
and R be an emtpy ruleset. That mean that

<R,S1> |=_simple <R,S2>  

Likewise, given  S3= {{ :s :p "blabla"^^xs:integer }}
would <S3,R> |=_simple <S,R> , where S is an arbitrary graph, i.e. 
is any combination with a graph containing an ill-typed literal inconsistent?

This means that simple entailment in combination with an empty ruleset 
is not the same as simple entailment in RDF... I think that should be 
pointed out explicitly. It would be also worthwhile to add this example,
i.e. I suggest to add (at the end of Section 3.2.3): 

"Note that simple entailment in combination with an empty ruleset 
is not the same as simple entailment in RDF, since certain entailments
regarding datatypes are enforced by the RIF-BLD semantics in
combinations. For instance, given two graphs

 G1= { :s :p "foo" .} and
 G2= { :s :p "foo"^^xs:string }

as well as an empty RIF document R.

 G1 |=/=_simpleRDF G2 

following [http://link-to-rdf-mt-simple-entailment RDF simple entailment] , but

 <R,{G1}> |=_simple <R,{G2}>
"

* Section 3.2.2

"Definition. Let (I, I) be a model of a combination C and let D be a
datatype map conforming with the set of datatypes in I"
-for clarification->
"Definition. Let (I, I) be a model of a combination C and let D be a
datatype map conforming with the set DTS of datatypes in I."


Section 4:
==========

*
"Since RIF frame formulas are interpreted using an extension function,
as in RDF, defining the correspondence between them and OWL 2 DL
statements would change the semantics of OWL statements, even if the
RIF document were empty."

Remark: As mentioned before, I think change of the semantics in
combination with an empty ruleset is already the case in RDF, not sure
whether you mean the same here.


*
"It is, however, also desirable that there be uniform syntax for the RIF component of both OWL 2 DL and RDF/OWL 2 Full combinations, because one may not know at the time of constructing the rules which type of inference will be used."
-->
"It is, however, also desirable that there be uniform syntax for the
RIF component of both RIF-OWL 2 DL and RIF-RDF/OWL 2 Full
combinations, because one may not know at the time of constructing the
rules which type of inference will be used."

* 
"the interpretation of frame formulas s[p -> o] in the RIF-OWL DL
combinations [...]"
-->
"the interpretation of frame formulas s[p -> o] in RIF-OWL DL
combinations [...]"


* "A combination consists of a RIF document and a set of OWL
  ontologies."

Again, I see no reason why not to define semantics in terms of sets of
RIF documents.


* "which are pairs of RIF and OWL 2 DL, respectively OWL 2 Full
  interpretations."
-->
 "which are pairs of RIF semantic (multi-)structures and OWL 2 DL,
  respectively OWL 2 Full interpretations."

* Section 4.1.1
"Given a set of OWL 2 DL ontologies O, a variable ?x in a RIF rule Q H
:- B is DL-safe if it occurs in an atomic formula in B that is not of
the form s[P -> o] or s[rdf:type -> A], where P or A occurs in one of
the ontologies in O."

That doesn't seem to be sufficient, take:

?X [rdf:type -> d ] :- Or ( ?X [rdf:type -> c ] p(?X) )

this is DL-safe according to the definition above but can be expanded
to two rule one of which wouldn't be DL-safe.

Rather, we need to adopt a safeness notion similar to Core.

* Section 4.1.2

"We note here that the definitions of datatype and datatype map in the
OWL 2 direct semantics specification OWL2-Semantics ... "
-add brackets around reference->
"We note here that the definitions of datatype and datatype map in the
OWL 2 direct semantics specification [OWL2-Semantics] ..."

same here:
"The definitions of datatype and datatype map we use are isomorphic,
and, indeed, the same as in the OWL 2 RDF-based semantics
specification OWL2-RDF-Based-Semantics."

* Section 4.2.1

There is one peculiar thing which I am wondering about:
since we talk about generalized RDF graphs in combinations 
and in the definition of entailment, does that mean that
generalized RDF graphs could be entailed by non-generalized ones?

particularly:

G1 = 
 :s :p :o

G2= 
 :o [] :p.
 
Would:
<R,{G1}> |= <R,{G2}> 
?

* Section 4.2.2.1


*
Definition (dl-semantic multi-structure):
"I<sub>1C</sub>, ..., I<sub>1C</sub>"

looks weird, better use 1...n as superscripts as in
http://www.w3.org/2005/rules/wiki/BLD#def-bld-semantic-multistruct

Again, shouldn't we use \hat{I} rather than I for
multi-structures as in BLD to be consistent?

*
same definition:
Bullet 1 ends with "and ; "
That looks incomplete, is there anything missing?

*
"I(&phi;), for any other formula or symbol &phi;, and the truth valuation
function TValI are defined as in BLD semantic structures. "

I am, honestly, getting confused with the definitions of
multi-structures in BLD vs. SWC.

dl-multistructures consist of {I_1, ..., I_n}
whereas BLD multistructures are {J,I; I_i1, I_i2, ...}
so, I am unsure what "defined as in BLD semantic structures."
means to say.

(BTW: I sent an amendment to my BLD review  per mail 
in this regard as well)

* Definition common-RIF-OWL DL-interpretation:
 
"(IR union LV) is D<sub>ind<sub>;"

looks visually a bit strange in my browser, since the ";" appears like a prime on "ind"
i.e. like " ind' " in the subscript and a strange dot on top... 
Suggest to add a space:

"(IR union LV) is D<sub>ind<sub> ;"

* Definition of model:

"(I, I) is an OWL DL-model of a DL-condition formula &phi if TVal_I(&phi;)=t."

See above, since dl-multi-structures don't talk about J, which seems
to be necessary to interpret non-document formulas, according to the
BLD definitions, I am a bit confused here how TVal_I(&phi;) is meant
to be defined.

Section 5
=========

*
"A RIF document contains a number of Import statements. Unary Import
statements are used for importing RIF documents, and the
interpretation of these statements is defined in [RIF-BLD]. 
"

Would be nice to directly link to the respective section:
[http://www.w3.org/2005/rules/wiki/BLD#Interpretation_of_Documents
Section 3.5]

i.e.

"A RIF document contains a number of Import statements. Unary Import
statements are used for importing RIF documents, and the
interpretation of these statements is defined in 
[http://www.w3.org/2005/rules/wiki/BLD#Interpretation_of_Documents
Section 3.5] of [RIF-BLD]."

*
"This section defines the interpretation of two-ary Import
statements:"

"two-ary" -- better? --> "binary" 

* 
General question:
What happens if a RIF documents imports ontologies, as well as other
RIF documents that respectively import ontologies?
Is that covered? Where/how?
That is, I am not sure whether/how this "recursive case" is covered in
Section 5.2.

Section 6
=========

* "Each RIF processor has sets T of supported datatypes and symbol
  spaces"
   ->
  "Each RIF processor has a set T of supported datatypes and symbol
  spaces"
  
  - that sentence is confusing is T the set of datatypes? the set of
    sumbol spaces?
  - mentioned before: I'd personally prefer to refer to sets of datatypes
    uniformly by DTS, instead of T. (There might be a reason for the
    distinction, I don't understand it, also made this remark to BLD.)
 
* 
"Formally, for any pair (&phi;, &psi;), where &phi is a BLDT,E-P
combination [...]"

I think you want to write here:

"Formally &mu; is a semantics preserving mapping *to* the language of L
if for any pair (&phi;, &psi;), where &phi is a BLDT,E-P
combination [...]"

*
"Formally, for any pair (&phi;, &psi;) of formulas in L [...]"

I am not sure what you want to say here, maybe:

""Formally ν is a semantics preserving mapping *from* the language of L
if for any pair (&phi;, &psi;), where &phi is a BLDT,E-P
combination [...]"
Received on Sunday, 17 May 2009 23:13:22 GMT

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