From: Christian De Sainte Marie <csma@fr.ibm.com>

Date: Mon, 9 Jul 2012 18:04:58 +0200

To: Jesse Weaver <weavej3@rpi.edu>

Cc: Adrian.Paschke@gmx.de, Ankesh <ankesh@cs.rpi.edu>, cawelty@gmail.com, public-rif-wg@w3.org, sandro@w3.org, team-rif-chairs@w3.org

Message-ID: <OF4EA37991.70A5DD6F-ONC1257A36.0057A4DB-C1257A36.00585C12@fr.ibm.com>

Date: Mon, 9 Jul 2012 18:04:58 +0200

To: Jesse Weaver <weavej3@rpi.edu>

Cc: Adrian.Paschke@gmx.de, Ankesh <ankesh@cs.rpi.edu>, cawelty@gmail.com, public-rif-wg@w3.org, sandro@w3.org, team-rif-chairs@w3.org

Message-ID: <OF4EA37991.70A5DD6F-ONC1257A36.0057A4DB-C1257A36.00585C12@fr.ibm.com>

Hi Jesse, Jesse Weaver <weavej3@rpi.edu> wrote on 05/07/2012 22:05:51: > > It appears that the operational semantics of RIF-PRD are > incompleteness wrt firing rules. Consider a set of facts \Phi = { > a#c , b#c } which represents a state of the fact base. Consider the > following rule: > > Forall ?x ?y ( > If And( ?x#c ?y#c ) > Then Do( (?v ?x[p->?v]) ?y[p->?v] ) ) > > The substitution \sigma = { <?x, a> , <?y, b> } matches condition > formula And( ?x#c ?y#c ) to \Phi. Therefore, by definition of > matching rule instance (section 4.2.3), the following is a matching > rule instance of the previous rule: > > If And( a#c b#c ) > Then Do( (?v a[p->?v]) b[p->?v] ) ) > > Suppose that the conflict resolution strategy selects only this rule > instance for firing. Then by definition of RIF-PRD production rule > system (section 4.2.4), the ground atomic actions derived from the > rule instance's action block are executed in sequence to transit to > the next state. From definition of action instance (section 4.2.3), > the action instance is derived by extending \sigma to another ground > substitution \sigma* = { <?x, a> , <?y, b> , <?v, d> } where d is a > constant such that a[p->d] \in \Phi. However, there exists no > constant d such that a[p->d] \in \Phi. Therefore, it is impossible > to derive an action instance for the given rule instance, and it > appears that such a case has an undefined operational semantics. > > What I wish to know is: have I correctly determined an > incompleteness in the semantics, and if so, what should the > operational semantics be in this case? I think this is on purpose: the rule is valid but does not have a semantics according to RIF-PRD if used in a context where the action variables cannot be bound. I started a discussion on the WG mailing list, though. > (Also, note that the definition of action instance requires that d > be a constant, which seems overly restrictive. What if a[p->List()] > \in \Phi, which is allowed by definition of frame atomic formula > (section 2.1.2) and definition of term (section 2.1.1).) Yes, you are right, this is a mistake. The second bullet in the definition of action instance should read: if vi is assigned the value of a frame's slot by the action variable declaration: (vi o[s->vi]), then ó(vi) is a ground term such that the subtitution ó matches the frame formula o[s->vi] to w. I will propose a correction in the revised edition. Thanx again for your comments. Cheers, Christian IBM 9 rue de Verdun 94253 - Gentilly cedex - FRANCE Tel./Fax: +33 1 49 08 29 81 Sauf indication contraire ci-dessus:/ Unless stated otherwise above: Compagnie IBM France Si?ge Social : 17 avenue de l'Europe, 92275 Bois-Colombes Cedex RCS Nanterre 552 118 465 Forme Sociale : S.A.S. Capital Social : 645.605.931,30 € SIREN/SIRET : 552 118 465 03644 - Code NAF 6202AReceived on Monday, 9 July 2012 16:05:43 GMT

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