Renata Wassermann. On structured belief bases. In Hans Rott and Mary-Anne Williams, editors, Frontiers in Belief Revision. Kluwer, 1999. To appear.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....by Nayak [26] and Darwiche and Pearl [9] Williams [36] uses the concept of maxi adjustment to achieve maximal inertia of information under iterated belief revision. The notion of epistemic relevance is used for minimal contraction in Hansson [18] and Nebel [27] Hansson and Wasserman ( 19] [35]) have developed models for local change and inconsistency tolerance based on relevance relations between formulas in the belief representation. The distinction between implicit and explicit beliefs, has been explored by the proponents of the belief base method such as Fuhrmann [14] Nebel [27] ....

Renata Wassermann. On structured belief bases. In Hans Rott and Mary-Anne Williams, editors, Frontiers in Belief Revision. Kluwer, 1999. To appear.

....and it is suggested that new information about one of them should not a ect the other. This ensures a relevance or context sensitive, localized notion of belief revision and serves as one way of capturing a more general notion of relatedness amongst propositions in a belief base (as studied by [Was99]) CP99] explicate the distinction between implicit and explicit beliefs by considering sets of theories called B structures, which are individually consistent, but can be jointly inconsistent. This captures the intuition that real agents often reason with an inconsistent, yet usable, set of ....

....upon the intuitions expressed in [Leh95] Under a temporal ordering the most recent formulae occur at the tail of the sequence. We assume that each formula in the sequence is expressed in its smallest language as de ned below. We now turn to a notion of relatedness amongst formulas in a sequence. [Was99] has proposed that inference from belief bases is made more plausible by assuming 2 the presence of some structuring relation amongst beliefs in a base. This relationship of relatedness facilitates the choice of beliefs to be revised, contracted or used for inference in any revision operation. We ....

Renata Wasserman. On structured belief bases. In Frontiers in Belief Revision, Kluwer Academic Publishers, Hans Rott and Mary-Anne Williams eds., 1999, to appear. 14

....IGPL, Vol. 0 No. 0, pp. 1 12 0000 c Oxford University Press 2 Approximate Belief Revision new information. There should be a way of isolating the subset of a belief base that contains the relevant beliefs for a query or an operation of belief change. Recent models such as [13] 9] 5] 6] [17], attempt to tackle the problem of plausible belief revision by using nonstandard inference operations such as local change operators and o ering structuring relations on belief bases via relevance sensitivity. In these frameworks for local reasoning and belief change, the key idea is that not all ....

....in [14] and in [16] is that there is no general strategy or heuristic for choosing the right set S for 6 Approximate Belief Revision the approximation. In this section, we argue for the use of a notion of relevance in order to guide the choice of the context set S. It has been shown in [6] and [17] that one way in which relevance in a database can be de ned is by looking at the syntactical structure of the formulas. In these studies, two formulas were considered relevant to each other if they shared an atom; the de nition was generalized to the case when formulas did not share an atom with ....

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Renata Wassermann. On structured belief bases. In Hans Rott and Mary-Anne Williams, editors, Frontiers in Belief Revision. Kluwer, 2000. to appear.

....not on belief bases. Another point which deserves more attention is the computational complexity of the construction suggested. The set B is still hard to compute, even if we only consider nite belief bases. But we can make the problem tractable by using local operations as suggested in [ Wassermann, 2001 ] so that the search space becomes small. This is left for future work. ....

Renata Wassermann. On structured belief bases. In Hans Rott and MaryAnne Williams, editors, Frontiers in Belief Revision. Kluwer, 2001. To appear.

.... Diagnosis Renata Wassermann Institute for Logic, Language and Computation University of Amsterdam email: renata wins.uva.nl Abstract In (Hansson Wassermann 1999; Wassermann 1999) we have presented operations of belief change which only affect the relevant part of a belief base. In this paper, we propose the application of the same strategy to the problem of model based diangosis. We first isolate the subset of the system description which is ....

.... Diagnosis Renata Wassermann Institute for Logic, Language and Computation University of Amsterdam email: renata wins.uva.nl Abstract In (Hansson Wassermann 1999; Wassermann 1999), we have presented operations of belief change which only affect the relevant part of a belief base. In this paper, we propose the application of the same strategy to the problem of model based diangosis. We first isolate the subset of the system description which is relevant for a given ....

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Wassermann, R. 1999. On structured belief bases. In Rott, H., and Williams, M.-A., eds., Frontiers in Belief Revision. Kluwer. to appear.

....or basic, beliefs that are implicit or merely derived, and beliefs that are active or in use. Besides the beliefs of the agent, the structure also represents provisional beliefs, i.e. sentences for which the agent has some evidence but is not yet sure whether to accept them or not. In [6] and [14], some ways of deciding which beliefs were active during an operation of belief change were explored. In this paper we turn to another question left open by the model, namely how to decide if a provisional belief should be accepted. Incoming information is usually given the highest priority, so ....

R. Wassermann. On structured belief bases. In H. Rott and M.-A. Williams, editors, Frontiers in Belief Revision (to appear). Kluwer, 2000.

....inactive, provisional and accepted. In section 3, we present a set of basic operations for belief change that can be applied to belief states. These operations can be combined to form more complex operations. This is illustrated in section 4, where we show how to define local change (Hansson and Wassermann, 1998) using belief states equipped with the basic operations. We will then discuss how Harman s principles can be interpreted in this framework. In section 6, we present some conclusions and point toward future work. In the rest of this paper, we will be working with a propositional language L, closed ....

....operations. This has been done in Wassermann (1997) In AGM there is no distinction between the sets of explicit and active beliefs, these sets may be infinite and the inference function used is a Tarski style consequence operation Cn. We will now show how the operations described in Hansson and Wassermann (1998) that make use of the set of active beliefs can be embedded in our framework. 4 Embedding Local Change In this section, we show how to model one of the local belief change operations described in Hansson and Wassermann (1998) local contraction, in the framework defined above. All the other ....

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Wassermann, R.: 1998, On structured belief bases, In Seventh International Workshop on Nonmonotonic Reasoning, Trento, 1998.

....or merely derived, and beliefs that are active, i.e. in use. Besides the beliefs of the agent, the structure also represented provisional beliefs , i.e. sentences for which the agent has some evidence but is not yet sure whether to accept them or not. In [ Hansson and Wassermann, 1999 ] and [ Wassermann, 1999a ] some ways of deciding which beliefs were active during a certain operation of belief change were explored. In this paper, we turn to another question left open by the model in [ Wassermann, 1999b ] namely how to decide whether a provisional belief should be accepted. According to [ Dung, ....

Renata Wassermann. On structured belief bases. In Hans Rott and MaryAnne Williams, editors, Frontiers in Belief Revision. Kluwer, 1999. to appear.

....2 fp; q; qg C p. This problem can be solved by leaving out inconsistent kernels: 1 (4) c 2 (ff; B) S ( B C ff) n (B C ) 1 This has the perhaps somewhat counterintuitive consequence that c(p; fp :pg) c(p; f g) Unless we adopt a syntax dependent approach (like the one in [Was99]) we will have to live with that. But this is insufficient, since negations are relevant. 2 We would like to have, for example: c(fqg; fp; p :q; r; r s; sg) fp; p :qg. This leads to a modification: 5) c 3 (ff; B) S ( B C ff) B C :ff) n (B C ) Note that the ....

Renata Wassermann. On structured belief bases. In Hans Rott and Mary-Anne Williams, editors, Frontiers in Belief Revision. Kluwer, 1999. to appear.

....either coming from the outside (new input) or from the inside (inference) has to survive inquiry before being incorporated into the existent beliefs. Since we allow for inconsistent beliefs and the agent 2 How do beliefs become active Two solutions for this question are presented in [HW98, Was98], where two different methods for activating the relevant beliefs are described. is not an ideal reasoner, an inference may well be rejected. That is why inferences should be at first only provisionally accepted. The depth of the inquiry is determined by the agent, by his interest on the ....

....( S ( B ff) B :ff) n (B ) We call c a compartmentalization function. This is only one way of defining a compartment. The representation results obtained in [HW98] do not depend on this particular construction. Another method for findind compartments of a belief base is presented in [Was98]. Local partial meet contraction is a local version of the construction for partial meet contraction given in [AGM85] and also makes use of a remainder operator and a selection function. A remainder operator selects for every set of sentences B and every sentence ff the maximal subsets of B that ....

Renata Wassermann. On structured belief bases. In Seventh International Workshop on Nonmonotonic Reasoning. Trento, 1998.

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