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Re: Reference vs import <-- RIF Core shortened

From: Gary Hallmark <gary.hallmark@oracle.com>
Date: Fri, 21 Nov 2008 13:25:13 -0800
Message-ID: <49272739.5010102@oracle.com>
To: Christian de Sainte Marie <csma@ilog.fr>
CC: Dave Reynolds <der@hplb.hpl.hp.com>, kifer@cs.sunysb.edu, Paul Vincent <pvincent@tibco.com>, Patrick Albert <palbert@ilog.fr>, "Boley, Harold" <Harold.Boley@nrc-cnrc.gc.ca>, Adrian Paschke <Adrian.Paschke@gmx.de>, Axel Polleres <axel.polleres@deri.org>, RIF WG <public-rif-wg@w3.org>

challenge accepted, so below

Christian de Sainte Marie wrote:
> Dave,
>
> thanx for the clarification.
>
> Here is how I understand PRD needs, at this point. Please, all, 
> complete and/or correct me:
>
> 1. Production rules needs subclass relationships. But in most, if not 
> all, cases, the class hierachy is fixed and there is, therefore, no 
> need to test it explicitely. However, it may be used by classification 
> tests, and it is, thus, needed in the semantics. Since it is, in most, 
> if not all, cases, externally defined, it has to be imported. But the 
> import can be specified without requiring that subclass relationships 
> be explicitely asserted in rules or facts.
>
> Hence, (my current understanding is that) PRD can do without ## in the 
> concrete syntax.
very odd to have ## in the abstract syntax and semantics but not let 
people use it.
>
> So, it would be interesting to challenge that assertion:
>
> 1a. What would be an use case where a subclass relationship test would 
> need be explicit in the condition of a rule (as opposed to the test 
> being carried silently as a consequence of importing the class 
> hierarchy)?
Here's a production rule I'd very much like to write if I'm trying to 
translate between RDF and Java objects:

if ?o # ?c1 and ?o # ?c2 and not(?c1 = ?c2 or exists( ?c ?o # ?c and ?c 
## ?c1 and ?c ## ?c2))
then ConstraintViolation("found an object that cannot have a Java Object 
Model")
>
> 1b. What would be an use case where a subclass relationship would need 
> be explicitely asserted in a fact (as opposed to being taken into 
> account as a consequence of importing the class hierachy)?
Let's say several vendors have RIF translators but not all have an 
import mechanism that works for Java objects, XML documents, and OWL 
ontologies.  An enterprising vendor could build a comprehensive set of 
importers that output standard RIF so it can be used with all the 
current and future RIF translators (assuming the RIF dialect supports # 
and ## facts, of course)
>
> 1c. What would be an use case where a subclass relationship would need 
> be asserted as a consequence of a rule (as opposed to the class 
> hierachy being immutable)?
I don't want to support this
>
> 2. Production rules need to test membership relationships, though. But 
> in most, if not all, cases, class membership is immutable. So that 
> class membership needs be asserted only at an object's creation. It 
> can thus be part of the semantics of the creation action (e.g. as 
> proposed in [1]).
>
> Hence, (my current understand is that) PRD can do with # being allowed 
> in tests and variable bindings only.
No, we need # and ## as facts to support the Import Vendor use case.
>
> The only challenge to that assertion that I can imagine would be an 
> use case for class membership assignement or mutation as a consequence 
> of a rule (but you all know how poor my imagination :-)
I don't want to support # and ## as conditional assertions, only as 
facts (i.e. unconditional)
>
> 2a. What would such an use case look like?
>
> 2b. Other ways to challenge the assertion, anyone?
> Dave Reynolds wrote:
>>
>> The proposal we discussed some weeks ago (but seem never to have 
>> formally adopted) was to only have # and only in rule conditions. 
>> That is appealing to be me because then I don't have to implement 
>> anything (if you can't assert data you can't test it!).
>
> The semantics of PRD is specified with respect to a data source. But, 
> as far as I understand, it does not require the data to be explicitely 
> asserted as facts (as opposed to being imported by reference to the 
> data source). So that, as soon as we will have specified that import, 
> it will be possible, in PRD at least, to have facts to test class 
> membership, whether PRD allows to assert facts or not...
>
> Cheers,
>
> [1] http://www.w3.org/2005/rules/wiki/Alt_AbstrAction
>
> Christian
>
Received on Friday, 21 November 2008 21:27:47 GMT

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