G. Grahne and A.O. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):241-252, February 1995.  Home/Search   Document Not in Database   Summary   Related Articles   Check

....we assume in this paper that the data and transition oracles are xed. Unfortunately, there is no general solution to the practical problem of how oracles can best be implemented. For the classical oracle described above, the problem has been partly solved by Grahne, Mendelzon, and Winslett [GM95; Win88] Winslett showed that, in general, the problem of updating propositional formulas is NP hard. Subsequently, though, Grahne and Mendelzon proved that updating sets of ground atoms with arbitrary propositional formulas can be done in polynomial time. More importantly, this result carries ....

G. Grahne and A.O. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):241-252, February 1995.

....This work is supported in part by Swedish Research Council for Engineering Sciences (TFR) under grant 282 95 966. 1 1 Introduction Incremental view maintenance plays an important role in integrity constraint checking in database systems [5, 2] and data warehousing in multi database systems [9, 11]. Recomputing views can be costly and may jeopardize transaction execution. It is therefore desirable to avoid the recomputation of views and to maintain views incrementally. Ceri and Widom [5] provided a facility to automatically derive set oriented active database rules from a view de nition for ....

....where materialized views are stored in a remote site, the full access to the base data may require a large amount of data to be transmitted via the network. Thus in recent years, considerable attentions have been paid to the problem of view maintenance without the full access to the base data [3, 4, 12, 10, 9, 11]. Previous studies have proved that only under strong conditions materialized views can be selfmaintained with respect to the updates of the base data. For example, an SPJ view that takes the join of two or more distinct relations is not self maintainable with respect to insertions into the base ....

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Gosta Grahne and Alberto O. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):241-252, February 1995.

....reasoning is nonmonotonic in the sense that by augmenting the knowledge base a previously valid counterfactual may become false. The relevance of counterfactual reasoning to a number of AI applications was first demonstrated in [ Ginsberg, 1986 ] to which (and to [ Gardenfors, 1988; Nebel, 1991; Grahne, 1991 ] the reader is referred for a background. In this paper we mainly deal with nested counterfactuals, i.e. counterfactuals where the conclusion can be a counterfactual itself instead of a plain propositional This is a short version containing only proof sketches. An extended report containing ....

....we will derive for nested counterfactuals are equally relevant to the problem of inferencing after iterated knowledge base revisions. The complexity of evaluating unnested counterfactuals over propositional knowledge bases, i.e. finite propositional theories, was considered in [ Nebel, 1991; Grahne, 1991; Eiter and Gottlob, 1992 ] In this paper, we deal with evaluating nested counterfactuals based on Ginsberg s approach [ Ginsberg, 1986 ] which uses the method by Fagin, Ullman and Vardi [ Fagin et al. 1983 ] for incorporating changes to a knowledge base. Such statements intuitively correspond ....

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Gosta Grahne and Alberto O. Mendelzon. Updates and Subjunctive Queries. Technical Report KRR-TR-91-4, University of Toronto, CS Dept., July 1991. Information and Computation, to appear.

....the current context if a minimal change to the belief base to accept leads necessarily to the acceptance of . Based on this idea, the complexity of evaluating conditionals using different revision and update schemes has been analyzed [ Eiter and Gottlob, 1992; Eiter and Gottlob, 1993; Grahne and Mendelzon, 1995 ] Grahne and Mendelzon [ 1995 ] approached the problem by assuming a model checking framework in that the belief base is represented as a set of models. Based on this assumption, they derive polynomial algorithms for evaluating conditionals under Winslett s update scheme provided that the ....

....a minimal change to the belief base to accept leads necessarily to the acceptance of . Based on this idea, the complexity of evaluating conditionals using different revision and update schemes has been analyzed [ Eiter and Gottlob, 1992; Eiter and Gottlob, 1993; Grahne and Mendelzon, 1995 ] Grahne and Mendelzon [ 1995 ] approached the problem by assuming a model checking framework in that the belief base is represented as a set of models. Based on this assumption, they derive polynomial algorithms for evaluating conditionals under Winslett s update scheme provided that the formula is fixed. Evaluating ....

Gosta Grahne and Alberto O. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):183--198, 1995.

....we assume in this paper that the data and transition oracles are fixed. Unfortunately, there is no general solution to the practical problem of how oracles can best be implemented. For the classical oracle described above, the problem has been partly solved by Grahne, Mendelzon, and Winslett [GM95; Win88] Winslett showed that, in general, the problem of updating propositional formulas is NP hard. Subsequently, though, Grahne and Mendelzon proved that updating sets of ground atoms with arbitrary propositional formulas can be done in polynomial time. More importantly, this result carries ....

G. Grahne and A.O. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):241--252, February 1995.

....a lower bound of their complexity is given by the complexity of the underlying non abductive operator. How complex these operators are depends on the class of KBs and the way the KBs are represented (models or set of formulas) Some results regarding the complexity of doing updates can be found in [10]. To the complexity of the underlying operator we must add the complexity of finding explanations. Again, this complexity will probably depend on the class of theories we choose to work with. Finding explanations in Horn theories will be probably easier than in more general theories. Results on ....

G. Grahne and A. Mendelzon. Updates and subjunctive queries. Information and Computation, 116(2):241--252, February 1995.

....to the problem of counting the classes of equivalence induced by a certain relation, and thus it is probably better characterized with one of the counting classes , such as #P. Note also that in this paper we have considered only the problem of revision, and not the related problem of update [GO95, FH94]. Finally, we relate our work with [EG93] In that paper, the authors analyze the complexity of inference in the (simple) iteration of the revision introduced by Fagin, Ullman and Vardi (also known as Ginsberg s revision) Other issues, related to the conditional logics are studied there. In our ....

G. Grahne and Mendelzon A. O. Updates and subjunctive queries. Information and Computation, 2(116):241--252, 1995.

....with the strata of the program in their hierarchical order. It is also interesting to note that hypothetical queries [Bon88, Gab85] and queries on re8 cursively indefinite databases [Mey90] can be expressed through updates. The connection between hypothetical queries and updates is explored in [GM95]. 3 Sample Transformations In this section we present seven example transformations. First we show that the common queries of transitive closure (Example 1) and parity (Example 6) can be expressed. We also show that the robots query described in the introduction can also be expressed (Example 4) ....

....if and only if after the projection 0 , the relation r 0 still contains the empty tuple, i.e. db 2 0 OE (kb) as required. Similarly to Theorem 4.5 this leads to the conclusion that the problem is not in NP [ co NP unless NP is closed under complement. 2 Remark: Grahne and Mendelzon [GM95] have studied the complexity of evaluating subjunctive queries in a propositional language, and found the data complexity of such a language to be in PTIME and the expression complexity to be in PSPACE. The quantifierfree case of our language does not have subjunctive implication operators in it, ....

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G. Grahne & A. O. Mendelzon. Updates and subjunctive queries. Information and Computation 116 (1995), 241--252.

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