Re: ISSUE-28: Recursion in the RIF Core

it's required for JSR-94.  I probably should have said, "all PR systems 
that support JSR-94 have a way to filter working memory after the rules 
have run"

Paul Vincent wrote:

><< all PR systems have a way to filter working memory after 
>the rules have run>>
>
>That's an interesting supposition. Care to elaborate?
>
>Paul Vincent
>TIBCO - ETG/Business Rules 
> 
> 
> 
>-----Original Message-----
>From: public-rif-wg-request@w3.org [mailto:public-rif-wg-request@w3.org]
>On Behalf Of Gary Hallmark
>Sent: 22 February 2007 22:14
>To: Michael Kifer
>Cc: Rule Interchange Format (RIF) Working Group WG
>Subject: Re: ISSUE-28: Recursion in the RIF Core
>
>
>Yes, I think all PR systems have a way to filter working memory after 
>the rules have run, so you could *filter* for "ancestor(John, ?x)".  
>More complex queries may be more challenging, e.g. ancestor(John, ?x) & 
>married(?x, Sally).
>Perhaps such a query could be rewritten by the PR-RIF translation 
>software as a rule "IF ancestor(John, ?x) & married(?x, Sally) THEN 
>answer(?x)".  This rule would be merged with the RIF ruleset(s).  
>Answers can then be collected using simple filtering. 
>
>Michael Kifer wrote:
>
>  
>
>>Gary,
>>A query is still a query. If you are asking for ancestors of John, you
>>    
>>
>should
>  
>
>>receive them in PR as well. It is just that PR will first compute the
>>    
>>
>whole
>  
>
>>thing first. Does Oracle's rule language have such postprocessing
>>filtering capabilities?
>>
>>
>>	--michael  
>>
>>
>> 
>>
>>    
>>
>>>My take-away from the email discussion on this issue is that PR can 
>>>express recursive rules just as well as Horn. 
>>>The real issue is how the rules are "executed". 
>>>
>>>With Horn (prolog), one "queries the KB" to execute rules.  The cool 
>>>thing about queries is that they can (optionally) pass in bound 
>>>variables to terminate the recursion.  E.g., with a simple factorial 
>>>ruleset, the queries "factorial(?x, 24)" and "factorial(4, ?y)" 
>>>terminate, whereas factorial(?x, ?y) does not.
>>>
>>>With PR, there is no query in the prolog sense.  One executes rules by
>>>      
>>>
>
>  
>
>>>giving a run(n) command, where n is the number of rules to fire.  If n
>>>      
>>>
>
>  
>
>>>is not specified, the PR system runs until no more rules fire.  
>>>Essentially, the run command is like a query with all variables
>>>      
>>>
>unbound, 
>  
>
>>>but instead of the "answer" being returned as a set of variable 
>>>bindings, the "answer" is left as a bunch of factorial tuples in
>>>      
>>>
>working 
>  
>
>>>memory. 
>>>
>>>So, I would withdraw the PR-recursion issue and raise a PR-query
>>>      
>>>
>issue.  
>  
>
>>>Per the charter,
>>>
>>>The core rule engine functionality is to load zero or more rulesets
>>>      
>>>
>(or 
>  
>
>>>datasets) and then answer zero or more queries against the merged 
>>>contents. This functionality is largely independent of engine 
>>>implementation strategies. (In particular, it works with both forward 
>>>chaining <http://en.wikipedia.org/wiki/Forward_chaining> and backward 
>>>chaining <http://en.wikipedia.org/wiki/Backward_chaining>.)
>>>
>>>We will have to be very careful about how to define a query against a
>>>      
>>>
>PR 
>  
>
>>>system.
>>>
>>>Nichols, Deborah L. wrote:
>>>
>>>   
>>>
>>>      
>>>
>>>>First, my apologies for a late posting of the recursion issue to the
>>>>Issues board.  Sponsor work has increased, and I haven't kept up to
>>>>date properly.  That said, however, I still want to record the issue
>>>>officially and clarify some aspects before stating the resolution.
>>>>
>>>>Axel's generalization of the issue makes an important point IMO.  If
>>>>the RIF Core allows "degrees of freedom" that not all rule languages
>>>>can express or implement, then should those features be restricted
>>>>        
>>>>
>(by
>  
>
>>>>putting them out of the Core) or restrictable (e.g., by profiles)?
>>>>
>>>>(Profiles is the next issue to be - finally - posted.)
>>>>
>>>>If we say that the Core should not be limited by what PR language can
>>>>handle (vs. what PR implementations can handle) - Paul's point - and
>>>>        
>>>>
>we
>  
>
>>>>leave recursion in, then will a difficulty arise when compliance is
>>>>defined?
>>>>
>>>>If we can come to a resolution by email, it isn't necessary to spend
>>>>meeting time on discussion.
>>>>
>>>>Regards,
>>>>Deborah
>>>>
>>>>-----Original Message-----
>>>>From: public-rif-wg-request@w3.org
>>>>[mailto:public-rif-wg-request@w3.org] On Behalf Of Paul Vincent
>>>>Sent: Tuesday, February 20, 2007 6:39 AM
>>>>To: Rule Interchange Format (RIF) Working Group WG
>>>>Subject: RE: ISSUE-28: Recursion in the RIF Core 
>>>>Importance: Low
>>>>
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>	I thought that we did sort out this issue. Namely, that
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>recursive 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>	clauses can be expressed by PR. I am also confused why did this
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>issue 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>	came back.
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>Gary suggested a scheme whereby it would be possible to map a
>>>>        
>>>>
>recursive
>  
>
>>>>PROLOG-type rule into a PR language (by effectively simulating bwd
>>>>chaining). And of course procedural extensions to PR languages can
>>>>certainly handle recursion (albeit not as "PR rules" per se). 
>>>>
>>>>But saying 
>>>>"PR language implementations can handle recursion" 
>>>>...does not equal 
>>>>"PR can handle recursion" 
>>>>(for me anyway). So this makes RIF Core "PR possible" rather than "PR
>>>>friendly". Hence, I assume, the "outstanding issue" for RIF. 
>>>>
>>>>But is it worth debating further? That would be my question.
>>>>
>>>>[Conjecture:]
>>>>Of course, the counterargument is that without recursion, RIF Core is
>>>>"meaningless" (as a rule language or maybe as a rule representation).
>>>>        
>>>>
>
>  
>
>>>>And of course, a countercounterargument is that RIF Core probably
>>>>*cannot* be a core subset covering all rule language semantics and
>>>>still
>>>>be a useful language in its own right (eg RIF Horn profile), and
>>>>        
>>>>
>indeed
>  
>
>>>>this should not be its goal: at best it should represent some common
>>>>expression representation scheme and/or a generalized rule metamodel
>>>>and/or rule classification scheme. 
>>>>
>>>>Just my 2 eurocents...
>>>>
>>>>Paul Vincent
>>>>TIBCO - ETG/Business Rules 
>>>>
>>>>
>>>>-----Original Message-----
>>>>From: public-rif-wg-request@w3.org
>>>>[mailto:public-rif-wg-request@w3.org]
>>>>On Behalf Of Michael Kifer
>>>>Sent: 20 February 2007 09:51
>>>>To: axel@polleres.net
>>>>Cc: Rule Interchange Format (RIF) Working Group WG
>>>>Subject: Re: ISSUE-28: Recursion in the RIF Core 
>>>>
>>>>
>>>>
>>>>I thought that we did sort out this issue. Namely, that recursive
>>>>clauses
>>>>can be expressed by PR. I am also confused why did this issue came
>>>>back.
>>>>
>>>>
>>>>	--michael  
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>Now I am a bit confused about that, to be honest, if I think it a
>>>>>          
>>>>>
>bit
>  
>
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>further:
>>>>>
>>>>>if we assume that RIF core should be common to ALL rules languages 
>>>>>around, would we also need to cut down other degrees of freedom
>>>>>          
>>>>>
>which
>  
>
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>Core allows: e.g. that we do not differentiate between the symbols 
>>>>>allowed for constants and function symbols, which some
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>systems/languages 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>do, that we allow the same symbol to be used with different arities,
>>>>>which some systems don't allow.
>>>>>Next, there are languages which e.g. restrict the allowed arity of 
>>>>>predicates and thus would neither cover all of RIF Core, e.g. SWRL
>>>>>only allows unary and binary preds in Horn rules.
>>>>>
>>>>>Would these then also be issues?
>>>>>
>>>>>I don't think we need to go that far. If we define the core really
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>only 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>as "what is expressible by any implemented rules system" then we'd 
>>>>>probably end up with propositional nonrecursive horn-rules with one 
>>>>>proposition in the antecedent?
>>>>>
>>>>>Probably I got this wrong, but it would be good if we define where
>>>>>          
>>>>>
>to
>  
>
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>draw the line, right?
>>>>>
>>>>>just my 2 cents,
>>>>>Axel
>>>>>
>>>>>Rule Interchange Format (RIF) Working Group Issue Tracker wrote:
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>>>ISSUE-28: Recursion in the RIF Core
>>>>>>
>>>>>>http://www.w3.org/2005/rules/wg/track/issues/28
>>>>>>
>>>>>>Raised by: Deborah Nichols
>>>>>>On product: Technical Design
>>>>>>
>>>>>>Issue:  Recursion in the RIF Core
>>>>>>Opened by Deborah Nichols [on behalf of RIF Chairs]
>>>>>>
>>>>>>This issue concerns whether or not to include recursion in the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>specification 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>of the RIF Core.
>>>>>>
>>>>>>Summary of an argument for exclusion:  
>>>>>>Assuming 
>>>>>>(1) that the RIF Core consists of positive Horn clauses and 
>>>>>>(2) that the RIF Core should be "common to" (i.e., translatable
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>into) all RIF 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>dialects, and 
>>>>>>(3) since positive Horn includes recursive formulas, 
>>>>>>then (4) if Production Rules cannot support recursion, 
>>>>>>the conclusion is (5) that would be no "compliant" PR dialect of
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>the
>>>>RIF 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Core.  
>>>>>>But it isn't acceptable not to have a PR dialect of RIF; 
>>>>>>therefore, (6) recursion should be "removed" from the Core.
>>>>>>(One method of "removal" would be to use profiles; see related
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>Issue.)
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Background and discussion:
>>>>>>
>>>>>>At F2F4, Gary Hallmark took an action [#188] to address the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>question
>>>>whether 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>recursive rules should be included in the RIF Core.  Of particular
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>concern was 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>the handling of recursion for Production Rule (PR) systems.  Gary
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>presented 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>the issue in email on 12 Dec 2006
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>(http://lists.w3.org/Archives/Public/public-
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>rif-wg/2006Dec/0035.html), questioning whether production-rule (PR)
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>systems 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>can support recursion and could implement a Core that included it.
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"The current proposal for a RIF Core is positive Horn clauses.
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>Such
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>clauses may be recursive, meaning that the relation name in the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>head
>>>>of 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>a rule also occurs (directly or indirectly) in the body of that
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>rule.  
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Because the semantics of a set of positive Horn clauses can be
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>defined 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>without reference to an evaluation strategy, an implementation is
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>free 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>to use something other than forward chaining.  In fact, most prolog
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>implementations use backward chaining.
>>>>>>
>>>>>>"The issue here is:  is there a general strategy to evaluate
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>recursive 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>positive Horn rules using forward chaining, so that every ruleset
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>in
>>>>RIF 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Core can be translated to production rules?  I don't really know
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>for
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>sure, but I suspect the answer is "no".  Here is a simple example
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>to
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>illustrate the problem ....[factorial example follows]"
>>>>>>
>>>>>>The implication for the RIF Core, as Gary stated later in the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>thread, is that:
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"As I understand it, RIF Core should be common to *all* RIF
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>dialects, 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>including a production rule dialect.  Now, it's clear that there
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>are 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>aspects of production rules that probably won't translate to Core
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>(e.g. 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>priority, retract).  That may be ok if we can add them to the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>dialect 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>without breaking the Core semantics.  On the other hand, it is
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>critical 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>that *everything* in Core can be translated to PR, otherwise we
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>have 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>dialects of Core itself, which means it really isn't a Core.
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>Therefore, 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>if Core supports recursive rules, then so should PR.   If we don't
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>think 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>it's practical to support recursive rules in PR, then we should
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>remove 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>this feature from Core."
>>>>>>
>>>>>>This issue is related to the "profiles" issue:  If RIF supports
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>profiles, then 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>recursion may be the most obvious feature to make "optional".  
>>>>>>
>>>>>>The recursion issue also has implications for defining conformance
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>to the RIF 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Core.  See Dave Reynolds' explanation 
>>>>>>
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>(http://lists.w3.org/Archives/Public/public-rif-wg/2007Jan/0079.html)
>>>>        
>>>>
>:
>  
>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"The specific issue that triggered a lot of this is the extent to
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>which 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>existing production rule engines can implement recursive Horn rules
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>and 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>so whether RIF Core should be RIF-Horn-without-recursion. Given a
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>target 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>query pattern (or some other context of use information) then a PR
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>RIF 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>translator can implement recursive horn rules but may be
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>non-terminating 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>for unrestricted queries. So either RIF has to convey that context
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>of 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>use, or the issue of ruleset termination is outside of RIF
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>conformance, 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>or we need some other notion of RIF Core."
>>>>>>
>>>>>>Chris Welty summarized the discussion of the nature of the Core,
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>from the 16 
>>>   
>>>
>>>      
>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>Dec telcon
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>(http://lists.w3.org/Archives/Public/public-rif-wg/2007Jan/0093): 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"We then went on discussing the nature of the CORE. The discussion
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>centered
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>on whether or not all languages were required to be able to
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>translate 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>FROM "all" of the CORE to be conformant.  Some continue to feel
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>this
>>>>is 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>unrealistic, however we lack examples that demonstrate it.  Several
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>expressed 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>support for a very limited notion of profiles for the CORE.
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>Profiles would 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>specify features that we may consider "optional" or that may
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>determine the 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>degree of conformance of a translation.  Examples of features in a
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>possible 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>CORE profile were: recursion, decidability, complexity bounds,
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>functions.
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"There seemed to be consensus that there is one core dialect with
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>the 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>expressivity of about Horn and that we should move forward with the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>specification of that dialect, independently of other
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>considerations.  If 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>there is a notion of profiles it should be extremely restricted so
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>that 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>the "CORE is still a core".  At the moment, we do not have any 
>>>>>>specific "features" of the CORE that anyone has objected to, except
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>possibly 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>recursive rules, so it is still not clear that we need profiles for
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>the CORE.
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>"We discussed whether RIF dialects must include and extend the
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>CORE.
>>>>The 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>possibility of profiles opens the door for some dialects to
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>eliminate certain 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>features (again, from a very restricted set).  In other words,
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>profiles may 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>allow some dialects to extend a subset of the CORE."
>>>>>>
>>>>>>Links to related email threads concerning PR and recursion:
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0035 
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0127
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>contains 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>discussion following on Gary's factorial example.
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Mar/0202
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0047.html
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>questions 
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>>>>whether recursion should be included in a PR system.
>>>>>>
>>>>>>Related threads on "recursive rules" vs. "recursive terms":
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0114 
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Dec/0103 
>>>>>>
>>>>>>An earlier (March 2006) discussion of recursion: 
>>>>>>http://lists.w3.org/Archives/Public/public-rif-wg/2006Mar/0106.html
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>
>>>>>>    
>>>>>>
>>>>>>         
>>>>>>
>>>>>>            
>>>>>>
>>>>>-- 
>>>>>Dr. Axel Polleres
>>>>>email: axel@polleres.net  url: http://www.polleres.net/
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>
>>>>>  
>>>>>
>>>>>       
>>>>>
>>>>>          
>>>>>
>>>>
>>>>
>>>>
>>>>     
>>>>
>>>>        
>>>>
>>>   
>>>
>>>      
>>>
>>
>> 
>>
>>    
>>
>
>  
>

Received on Monday, 26 February 2007 17:35:44 UTC