<ChrisW> Chair: Christian de Sainte-Marie

<csma> leora, would you scribe, please?

okay

<csma> Thank you

<ChrisW> scribenick LeoraMorgenstern

<ChrisW> scribenick: LeoraMorgenstern

<ChrisW> Scribe: Leora Morgenstern

Administration

Meeting for December 26th has been cancelled;

ACTION 194 (on ChrisW) to update people with multiple actions has been closed.

<ChrisW> RESOLVED: accept minutes of 12/12 telecon

Minutes of December 12 have been accepted

Amendment to agenda: We will not discuss issue 12, since Dave (Reynolds) is not here.

That will be moved to the next meeting.

Face to Face Meetings

ACTION 201 on Sandro to set up web page for registration: continued

<Allen> no

Liaison

III: No actions; no news

IV: Technical Design

Technical Design

csma: any discussion on use of constraints in RIF?

ChrisW: (to Harold and Michael) Did Hassan's paper clear up the confusion

Harold: little confusion about CLPs

cmsa: Alex and Dave were concerned about CLPs, but they are not present at this call.

csma: Continuing to slotted syntax ...

hassan: Not much contention on uses of constraints.
... idea is not to impose the clp scheme, but the idea of using constraints to abstract data
... two orthogonal dismensions: rules, and data they work on

cmsa: connection to black boxes discussed at f2f?

Harold: can be handled by the same mechanism

Hassan: constraints used for pattern matching, is the mechanism for binding variables

ChrisW: isn't using too much unsspecified and relying on external calls a form of cheating?

Hassan: No --- won't be unsspecified

csma: objection is to phrase "external call"

Hassan: But can use a logical system for solving constraints

<Harold> Basic semantics of an external call: map current substitution (binding environment) to a new substitution (indicating success) or to failure.

<FrankMcCabe> +q

Hassan: unifying is the external call: external to CLP engine
... taking the "external call" too literally, It just means that two things are independent.

csma: to avoid confusion, change term "external call"

Michael: question about extensibility of CLP schema
... (to Hassan): how does CLP scheme extend to negation as failure, for example?

Hassan: Can be extended to handle NAF

csma: extension to production rules?

Hassan: hard to extend to production rules --- don't have complete operational semantics
... if it can be expressed in LP, can be expressed in CLP

Michael: But: is there a model-theoretic characterization for constraint stable models as there is for stable models in LP?
... want stable semantics or well-founded semantics for CLP.

Hassan: Has to look it up to formalize question, see if it has been addressed, see if satisfies Michael's requirements

<Zakim> GaryHallmark, you wanted to ask whether constraints == prolog builtins

Gary: are Prolog built ins = constraints? predicates?

Hassan: Prolog built ins are black boxes; can be viewed as contraints

<igor> in Prolog, term unification=constraints

csma: if one of the & (?) in the RIF is doing Prolog, and another is doing something else, what do we have / where do we stand?

hassan: encoder makes decision

<Harold> Christian, we could say that an "external call" need not be a "foreign call": "External" in the sense of "normally independent of RIF", although in special cases it can coincide with RIF. "Foreign" in the sense of "software entirely outside of RIF".

<ChrisW> Polo, who are you?

csma: how do you decide what goes into constraints and what goes into conditions, if your langauge doesn't have this distinction?
... question is not just for production rules.

Gary: Prolog built-ins can have side effects; in production rules, these would have to be implmented in action part.

Hassan: in the scheme, putting things on the right does not say anything about execution order.

<Harold> Gary is referring to http://www.w3.org/2005/rules/wg/wiki/CORE/Rules/Horn, SYNTAX, Example 3b'.

Hassan: Gary's example is outside the scheme (check on this)

<ChrisW> uh oh

csma: but how would implementer know what to do for an arbitrary rule language?

Hassan: normative syntax should be constraint syntax;

<FRancois> Yes, it is.

<AxelPolleres> hmmm.

<Hassan> hmmm?

Frank: it's not that clear; some people use rules to implement constraints.

Distinction between normal rules and constraint rule can be subtle.

<AxelPolleres> I am still unclear where the line between built-ins and constraints lies, but I was a bit distracted, for a moment, sorry.

Frank: distinction between what's in constraints and what's in rules is up to author.

<Harold> Frank and Hassan, one clear criterion for relations that should go into constraint calls would be decidability. Only decidable relations should become constraints.

Frank: Most often, people have a set of predicates that they choose to call contraints.

Hassan: That's exactly my point!

<GaryHallmark> a Java method can be very fast at solving some kind of constraints, but it only works if some variables are bound. Is this allowed?

<Harold> (Not all decidable relations would need to become constraints, so *efficient* decidability could be a more strict criterion.)

Frank: whole issue of slotted vs positional arguments can be viewed in terms of constraints.

Harold: could have some predefined library of constraints: perhaps built-in libraries that comes with RIF.

Hassan: Really likes Harold's idea.

<AxelPolleres> +1 to have a list of built-ins.

Harold: lots of discussion about which are the right built-ins.

<AxelPolleres> can Xpath/Xquery functions be a starting point?

csma or ??: built ins would be on constraints, for efficiency reasons. (Check this.)

<ChrisW> Axel, that is a place for us to look, I think (Xpath/Xquery)

Harold: No need to change semantics for slots.
... change change syntax to transform slots into positional arguments.

<GaryHallmark> URL?

(This is on wiki Core)

positive conditions --- syntactic transformations

Harold: details about the transformation ...

<Hassan> Where is this on the wiki?

Harold: all can be implemented nicely using Hassan's CLP

http://www.w3.org/2005/rules/wg/wiki/CORE/Conditions/Positive

csma: can you do the transformation in the other direction as well?

Harold (to csma): yes

Frank: confused about bottom element
... slotted to positional; you would expect missing slots to map to any variable

Hassan: yes, should map to top element

Harold: depends on semantics. minimalistic semantics: yes

<Hassan> Then what does bottom denote? It denotes constraint failure to me!

Harold: bottom denotes variable that doesn't bind to anything

Hassan: no, that's not the semantics for bottom.
... It's top, not bottom!

<FRancois> Sorry, friends, I must go.

Hassan: this is a very strange version of extensional records of functional programming
... was suggested ?? years ago by ??? (check)
... why do this? can be much more simply handled

<AxelPolleres> Can we wrap this up and move it to the list?

csma: can't solve this now. Can Harold's version on wiki be modified?

ChrisW: Point of Harold's document was that there be no rest variables (check this)

<PaulaP> I wish you relaxed holidays!

Hassan: But this can be solved much more simply --- don't need extension variables

<PaulaP> bye

ChrisW: (to Hassan) unclear about your position on signatures

Hassan: yes, you do need signatures

ChrisW: for Hassan, signatures are a way of solving the problem

Harold: want to do this statically
... don't want constraints in condition part

<FrankMcCabe> you can achieve the same effect by mapping f(a=1,b=2) to f/2(1,2)

csma: Hassan, please go to Harold's wiki page and suggest ways of modifying it.

Hassan: my paper already explains it.

csma: paper is not the same as a RIF document/proposal

Hassan: all right, one more try. Too much workload to persist in this.
... But I'm taking no new actions until January

<Harold> Right, "Point of Harold's document was that there be no rest variables (check this)": No rest variables (no 'subsumption' or 'open-slot' semantics) to avoid the problem we had after F2F4, namely that, e.g., p(a,b) would be 'equal' to p(a) through the shortcut of p{1->a,2->b} being equal to p{1->a}.

csma: let's move to production rules

Gary: trying to clarify interaction with the rules system --- no straightforward way to transform LP rule to production system

<Hassan> As Harold wrote it in one email, transforming top-down to bottom-up rule evaluation

ChrisW: Suggestion from Gary: pragmas in the translation.

<Hassan> is done with Magic sets

<sandro> [ I'm deeply sorry -- I had to step out of the meeting there to handle an urgent personal matter. ]

csma: pragmas related to RIF processing models?

<sandro> [ back now, though ]

<AxelPolleres> MAgic sets are an optimization method for "emulating" top-down wthin bottom-up evaluation of rule sets

<Harold> I wonder about Francois' SATCHMO, ... experience here (top-down plus bottom-up).

ChrisW (to csma): could be

Frank: Does Chris mean that pragmas should capture operatoinal semantics of the rules?

Chris: Has to think about this more

csma: need examples

<AxelPolleres> -1

Frank: can't capture essence of rules if operational semantics is ignored.

<AxelPolleres> to that operational semantics is essential in all cases.

csma: Discussion probably needs to be put back on mailing list.

<Hassan> Yes, but how many "pure" such language vs. "dirty" rule langues?

Axel: was disagreeing that operational semantics is always essentia. After all, one can have a model theoretic semantics

ACTION 188 closed

<AxelPolleres> please post the URIs again in the minutes to these actions to have a hook here.

ACTIONS 156, 157, 159, 160 all continued

<AxelPolleres> bye

<Hassan> +1 to adjourn

<Hassan> Happy many things

http://www.w3.org/2005/rules/wg/track/actions/open

<ChrisW> sandro?