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Re: [DTB] summary of editorial issues (completes ACTION-552)

From: Axel Polleres <axel.polleres@deri.org>
Date: Wed, 27 Aug 2008 15:31:28 +0100
Message-ID: <48B56540.2020500@deri.org>
To: Jos de Bruijn <debruijn@inf.unibz.it>
CC: "Public-Rif-Wg (E-mail)" <public-rif-wg@w3.org>

Jos de Bruijn wrote:
> <snip/>
> 
>> 3) In the course of the rdf:text discussions, we discussed that a
>> function/predicate for implementing language-pattern matching according
>> to subtag matching according to RFC4647 is needed. (This is not yet
>> reflected by an editor's not in the current draft.) I propose
>> to add:
>>
>> pred:matches-langtag( ?arg1 , ?arg2 )
>>
>>  intended domains:
>>    - arg1 rdf:text
>>    - arg2 valid language range according to
>>        http://www.rfc-editor.org/rfc/rfc4647.txt
> 
> Why would this be necessary/useful?  We already have a function for
> extracting language tags.
> 
> pred:matches-langtag( ?arg1 , ?arg2 )
> is the same as
> func:lang(?arg1)=?arg2

jos, if you mean that the same functionality could be achieved with

   pred:matches

(http://www.w3.org/2005/rules/wiki/DTB#pred:matches_.28adapted_from_fn:matches.29)

then the answer is: yes and no

lang-pattern-matching in
  http://www.rfc-editor.org/rfc/rfc4647.txt
is different from regular expression  matching in pred:matches.

For example, the extended language range "en-*-US" maps to "en-US"
(English, United States), also matching is case insensitive, which is 
quite different from matching a regexp (although I don't say it can't 
all be expressed in a regexp, this regexp might become fairly nasty)

Since lang-pattern wildcards are still something which seems to be often 
used in connection with language tags, I suggest to have a separate 
function for that.

> <snip/>
> 
>> 5) Editor's Note: It was noted in discussions of the working group, that
>> except guard predicates, also an analogous built-in function or
>> predicate to SPARQL's datatype function is needed. This however has some
>> technical implications, see
>> http://lists.w3.org/Archives/Public/public-rif-wg/2008Jul/0096.html
>>
>> PROPOSED: We could  - analogous to  pred:iri-to-string, define predicates
>>
>>  pred:matches-datatype( ?arg1 ?arg2)
>>
>> such that the predicate is true iff ?arg1 is in the value space of
>> the datatype denoted by ?arg2 . An open question is whether we should
>> use the rif:iri or the string representing the datatypeIRI for the
>> second argument, i.e. what is the intended domain for ?arg2 ??
> 
> I don't really see how this could be defined in a meaningful way.  In
> any case, we already have the guard predicates, so I don't see the use.

The use case is simple: I want to emulate the datatype function from 
SPARQL in RIF... I want to know whether a literal is an integer or a
decimal. It is quite obvious, that we can't define a function which does 
this, the predicate is an alternative suggestion, I will not fight for 
it if no one else sees the need to at least cover the expressivity of 
the built-ins in SPARQL... although I find this awkward at least.

  <snip/>
> 
>> 7) Editor's Note: In the following, we adapt several cast functions from
>> [XPath-Functions]. Due to the subtle differences in e.g. error handling
>> between RIF and [XPath-Functions], these definitions might still need
>> refinement in future versions of this draft.
>>
>> Indeed I need to check back Jos exact concerns here, he thought that
>> referring to the [XPath-Functions] conversions is not precise enough
>> here, see also 8)
> 
> Basically, the interpretations of the functions are not completely defined.

yes.

>> 8) Editor's Note: We might split this subsection into separate
>> subsections per casting function in future versions of this document,
>> following the convention of having one separate subsection per
>> funtcion/predicate in the rest of the document. However, it seemed
>> convenient here to group the cast functions which purely rely on XML
>> Schema datatype casting into one common subsection.
>>
>> I can separate them, if the majority of the working group thinks this is
>> necessary.
> 
> I'd say: either follow the principle of having one subsection per
> predicate/function (I personally don't see the use of that) or don't
> follow this principle.
> in the former case, you need to split up the mentioned subsection.  In
> the latter case, many subsections in the document can be merged.

yes.

>> 9) Editor's Note: The cast from rif:text to xs:string is still under
>> discussion, i.e. whether the lang tag should be included when casting to
>> xs:string or not.
>>
>> PROPOSED. replace rif:text by rdf:text, otherwise leave as is.
> 
> I don't remember whether we discussed this in the working group.

yes, it needs to be discussed/approved. casts from rdf:text to xs:string 
are not covered by standard conversions in XPath/XQuery, but the 
suggested treatment covers it analogously to:

    http://www.w3.org/TR/rdf-sparql-query/#func-str

> <snip/>
> 
>> 12) Editor's Note: The working group is currently discussing, whether in
>> addition to adopting the fn:compare function from [XPath-Functions], own
>> predicates pred:string-equal, pred:string-less-than,
>> pred:string-greater-than, pred:string-not-equal,
>> pred:string-less-than-or-equal, pred:string-greater-than-or-equal not
>> defined in [XPath-Functions] shall be introduced, following the
>> convention of having such predicates for other datatypes.
>>
>> PROPOSED: introduce additional comparison predicates.
> 
> Why would we want to have these comparison predicates and what does it
> mean for one string to be less than another?

Suggested by Gary, the idea is to have uniformity, i.e. predicates
less-than, greater-than, equal, less-than-or-equal, 
greater-than-or-equal, for all (or ate least most) datatypes, where this 
can be defined in a feasible manner.

If there is disagreement here for the sake of redundancy,
then we also have to revisit the and  less-than-or-equal, 
greater-than-or-equal predicates which were approved by the group, since 
they are likewise superfluous.

>> 13) Editor's Note: No less-than-or-equal or greater-than-or-equal
>> predicates are defined in this draft for durations, since there are no
>> separate op:dayTimeDuration-equal nor
>> op:yearMonthDuration-equalpredicates in [XPath-Functions], but only a
>> common predicate op:duration-equal. Future versions of this working
>> draft may resolve this by introducing new equality predicates
>> pred:dayTimeDuration-equal and pred:yearMonthDuration-equal with
>> restricted intended domains.
>>
>> PROPOSED: introduce a single predicate duration-equal that only
>> evaluates to true if the arguments are both of the same duration subtype
>> and equal.
> 
> Agreed.
> 
>> 14) Editor's Note: Predicates for rdf:XMLLiteral such as at least
>> comparison predicates (equals, not-equals) are still under discussion in
>> the working group.
>>
>> PROPOSED: introduce equals and not-equals for XMLLiteral which matches
>> modulo white-spaces in non-text content.
> 
> Two XML literals are equal if their values (as defined in [1]) are the
> same and not-equal if their values are not the same. I cannot imagine
> any other meaningful definition for equality of XML literals.
> 
> [1] http://www.w3.org/TR/rdf-concepts/#section-XMLLiteral

ok, that doesn't include white-space normalization or alike...
for that actually "=" suffices, doesn't it?

If the group is fine with

pred:XMLLiteral-not-equals("<a/>"^^rdf:XMLLiteral
                            "<a />"^^rdf:XMLLiteral)

then fair enough. As far as I understood, XML prescribes some 
normalization of end-of-lines

  http://www.w3.org/TR/2000/REC-xml-20001006#sec-line-ends

and for white spaces in attribute values

  http://www.w3.org/TR/2000/REC-xml-20001006#AVNormalize

Do we need to bother about this?



>> 15) Editor's Note: The current name of this function is still under
>> disscussion in the working group. Alternative proposals include e.g.
>> func:lang-from-text, which follows the XPath/XQuery naming convention
>> for extraction functions from datatypes than the SPARQL naming convention.
>>
>> PROPOSED: change to func:lang-from-text and only add a remark that this
>> is related to SPARQL's lang-function.
> 
> Agreed.
> 
>> 16) Editor's Note: We have not yet included comparison predicates
>> (equal, less-than, greater-than, or compare ...) for rif:text. Future
>> versions of this document might introduce these.
>>
>> PROPOSED: only add equal and not-equal for rdf:text, for more
>> sophisticated comparisons conversions to strings and the more
>> fine-grained comparisons on  strings can be used.
> 
> Agreed.
> 
> 
> 
> Best, Jos
> 


-- 
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 Wednesday, 27 August 2008 14:32:12 GMT

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