Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the 4th International Conference on Principles of Knowledge Representation and Reasoning, pages 178--189, San Francisco, CA, June 1994.  Home/Search   Document Details and Download   Summary   Related Articles   Check

....be excluded. It may be possible to recognise a restricted class of these cases for which a suitable tactic can be found. Closed World Knowledge Baldric does not make the closed world assumption. Instead it keeps track of those aspects of the world over which it has local closed world knowledge [3, 4]. In general LCW will be conditional, for example Baldric may have closed world knowledge of the number of elephants in the room of the robot it is controlling, but not in any arbitrary location : KW (N:number of elephants in location(N; L) current location(Baldric; L) If Baldric fails to ....

Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. Knowledge Representation, 1994. 14

....execute query access plans. The planner is based on an implementation of UCPOP [Barrett e al. 1993] We augmented this planner with the capability for producing parallel execution plans [Knoblock, 1994] added the capability of interleaving planning and execution [AmbrosIngerson and Steel, 1988, Etzioni e al. 1994], and added support for run time variables [Ambros Ingerson and Steel, 1988, Etzioni e al. 1992] for gathering information at run time. This work extends previous work on interleaving planning, execution, and sensing with the ability to perform these operations in parallel and applies these ideas ....

....is also quite broad and the related work has focused on various issues. Kahn and Cerf [Kahn and Cerf, 1988] proposed an architecture for a set of information management agents, called Knowbors. The various agents are hard coded to perform particular tasks. Etzioni et al. Etzioni et at. 1992, Etzioni et at. 1994] have built agents for the Unix domain that can perform a variety of Unix tasks. This work has focused extensively on reasoning and planning with incomplete information, which arises in many of these tasks. In contrast to this work, the focus of our work is on flexible and efficient retrieval of ....

Oren Etzioni, Keith Golden, and Dan Weld. Tractable closed-world reasoning with updates. In Fourth International Conference on Principles of Knowledge Representation and Reasoning, Bonn, Germany, 1994. Bibliography 27

.... :closed world and :open world relation properties) and CLASSIC [20] which allows roles to be declared to be closed ) This notion has also been formalised in description logic by the use of epistemic operators that modify roles, and in AI planning by the use of local closed world formulae [21]. The notClosedOn property used in this work should also include a reference to the current RDF model, but this is not currently possible as RDF does not provide a way to declare that a set of statements collectively constitute a model with a given URI. 6 Reasoning with OCL The Semantic Web, as ....

O. Etzioni, K. Golden, and D. Weld. Tractable closed world reasoning with updates. In L. Doyle, E. Sandewall, and P. Torasso, editors, KR'94: Principles of Knowledge Representation and Reasoning, pages 178-- 189. Morgan Kaufmann, San Francisco, California, 1994.

....to the database. Under the open world assumption, the extensions of the views may be missing tuples (but they may not have incorrect tuples) The open world assumption is especially appropriate in data integration applications, where the views describe sources that may be incomplete (see [EGW94, Lev96, Dus97] for treatments of complete sources) The closed world assumption is appropriate for the context of query optimization and maintaining physical data independence, where views have actually been computed from existing database relations. Under the open world assumption, AD98] show ....

Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the Conference on Principles of Knowledge Representation and Reasoning, KR-94., 1994. Extended version to appear in Artificial Intelligence.

....between the contents of data sources and relations in a mediated schema can be speci ed using limited forms of logic, and illustrated the associated reasoning algorithms. There are additional areas in which logic based techniques have been applied, including descriptions of source completeness Etzioni et al. 1994; Levy, 1996; Duschka, 1997, and descriptions of query processing capabilities of data sources Levy et al. 1996c; Vassalos and Papakonstantinou, 1997. Logic Based Techniques in Data Integration 21 There are two areas in which I believe signi cant future research is required. The rst area ....

Etzioni, O., Golden, K., and Weld, D. (1994). Tractable closed world reasoning with updates. In Proceedings of the Conference on Principles of Knowledge Representation and Reasoning, KR-94. Extended version to appear in Articial Intelligence.

....on theoretical issues of planning algorithms. Recent work has concentrated on, for example, the relative performance of total order vs partial order planners [3, 57, 44] the inherent computational complexity of plan generation [6, 23] extending the expressiveness of the classical 1 model [25], and general, theoretical frameworks for planning engines [31] This research has been dominated by the use of the literal or proposition as the basic level of representation, and operators representing actions, as the basic knowledge structure, containing formulae made up of these literals. ....

O. Etzioni, K. Golden, and D. Weld. Tractable Closed World Reasoning with Updates. In Proceedings Knowledge Representation Conference, 1994.

....allows for positive datalog programs. Such limitations in the representational power restrict the range of application of hybrid KR systems. Specifically, the lack of nonmonotonic features in the relational subsystem makes it hard to deal with the relevant notions of information completeness [ Etzioni et al. 1994, Duschka and Genesereth, 1997 ] and disjunctive information sources [ Duschka and Genesereth, 1998 ] in the mentioned applications to heterogeneous information systems, while the restrictions in the description logic language impose drastic approximations in modeling relationships among ....

O. Etzioni, K. Golden, and D. Weld. Tractable closed-world reasoning with updates. In Proc. of the 4th Int. Conf. on the Principles of Knowledge Representation and Reasoning (KR'94). Morgan Kaufmann, Los Altos, 1994.

....sources. For example, if our query asks whether a certain person authored a paper in SIGMOD 98, we need only consult the DB LP bibliography, and not other sources that may contain overlapping data. Local completeness assertions were first considered in the context of the Internet Softbot project [EGW94] In that work, the authors considered statements of the form: 3 LCW (V 1 (title; director; year) American(director) year 1960) meaning that the movie source is complete with respect to films produced by American directors after 1960. These statements were shown to be a restricted form of ....

....does Q 0 produce the complete answer for Q For example, if the user asks for titles of recent American comedies, the source above would provide a complete answer, but if the user also asks for reviews of such movies then the answer may be incomplete if our review sources are incomplete. In [EGW94] the authors describe several rules for inferring completeness statements for queries. In [Lev96] is it shown that this inference problem is closely related to the problem of deciding whether a database query is independent of an insertion or deletion update to the database. This relationship ....

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Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the Conference on Principles of Knowledge Representation and Reasoning, KR-94., 1994. Extended version to appear in Artificial Intelligence.

....s 1 and s 2 store the father and mother relation, respectively. s 1 (X; Y ) Gamma parent(X; Y ) male(X) 5 Several authors have distinguished the case in which the source contains all the tuples that satisfy the query from the case in which some tuples may be missing from the source [13,14,9,21,1]. For our discussion this distinction does not matter. s 2 (X; Y ) Gamma parent(X; Y ) female(X) Given a query Q from the user, the mediator needs to formulate a query plan, which is a query that bottoms out in the source relations and produces answers to Q. A query plan is a set of Horn ....

O. Etzioni, K. Golden, and D. Weld. Tractable closed world reasoning with updates. In Proceedings of the 4th International Conference on Principles of Knowledge Representation and Reasoning, pages 178--189, San Francisco, CA, June 1994.

....general, sources that we find on the WWW are not necessarily complete for the domain they are covering. For example, a Computer Science bibliography source is unlikely to contain all the references in the field. However, in some cases, we can assert local completeness statements about sources [EGW94] For example, the DB LP Database 1 contains the complete set of papers published in some of the major database conferences. Knowledge of completeness of a web source can help a data integration system in several ways. Most importantly, since a negative answer from a complete source is ....

Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the Conference on Principles of Knowledge Representation and Reasoning, KR-94., 1994. Extended version to appear in Artificial Intelligence.

....has been studied extensively (Levy et al. 1995; Rajaraman, Sagiv, Ullman 1995; Levy, Rajaraman, Ordille 1996a; 1996b; Duschka Genesereth 1997a; 1997b; Duschka Levy 1997) little work has been done on query plan optimization. We show how local completeness information as introduced in (Etzioni, Golden, Weld 1994) and explained in the following can be used for query plan optimization in the source centric approach to information integration. Local completeness Information brokers communicate with users in terms of a global scheme consisting of a set of world relations p 1 ; p 2 ; pm . The broker ....

Etzioni, O.; Golden, K.; and Weld, D. 1994. Tractable closed world reasoning with updates. In Proc. 4th KR, 178--189.

....gathering. The problem of information gathering is also quite broad and the related work has focused on various issues. Kahn and Cerf [ 1988 ] proposed an architecture for a set of information management agents, called Knowbots. The various agents are hard coded to perform particular tasks. Etzioni et al. 1992, 1994 ] have built agents for the Unix domain that can perform a variety of Unix tasks. This work has focused extensively on reasoning and planning with incomplete information, which arises in many of these tasks. Levy el al. 1994 ] are also working on building agents for retrieving information from ....

Etzioni, Oren; Golden, Keith; and Weld, Dan 1994. Tractable closedworld reasoning with updates. In Fourth International Conference on Principles of Knowledge Representation and Reasoning, Bonn, Germany.

....we have developed a planning system that builds on the previous work on planning, execution, sensing, and replanning. The planner, which we call Sage, was implemented by augmenting ucpop [17, 4] with the capabilities to produce parallel execution plans [13, 20] interleave planning and execution [2, 7], support run time variables [2, 8] and perform replanning where appropriate [10] We have integrated all of these capabilities into a single unified system in which the actions can be executed simultaneously, and the planning, sensing, and replanning can be performed during execution. This ....

....run time variables for sensing. Owalski and Gini [16] focused on the tradeoffs and strategies in choosing when to sense and when to plan. Etzioni et al. developed a language for representing incomplete information [8] and built an integrated system for planning, execution, and sensing called XII [7] that can represent and reason about locally complete information. This paper extends this earlier work within the classical planning paradigm with the capability to perform the planning in parallel with the execution. This allows the system to execute actions in parallel, handle new goals as they ....

Oren Etzioni, Keith Golden, and Dan Weld. Tractable closed-world reasoning with updates. In Fourth International Conference on Principles of Knowledge Representation and Reasoning, Bonn, Germany, 1994.

....meaning of an answer to a given query needs to be reconsidered. For queries that do not contain negation, the answers we obtain are guaranteed to be a subset of the answers that would have been obtained if the database were complete. However, an important question (considered originally in [Mot89, EGW94] is whether the answer is complete even though the database is incomplete. When queries contain negation, we need to modify our query answering algorithms to guarantee that we obtain only correct answers. We consider the answer completeness problem, i.e. deciding whether an answer to a given ....

....a query, it is important to know which sources (or combination of sources) provide all the answers to the query. If we cannot obtain all the answers, we need to query multiple sources, thereby considerably affecting the performance of the system. Experimental results reported by Etzioni et al. EGW94] showed that identifying answer completeness of queries enables pruning many redundant accesses to information sources, and therefore to significant speedups in query processing. Finally, the answer completeness problem is also important in other contexts. For example, during a long transaction, ....

[Article contains additional citation context not shown here]

Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the Conference on Principles of Knowledge Representation and Reasoning, KR-94., 1994. Extended version to appear in Artificial Intelligence.

....(and I m undoubtedly unaware of an existing body of literature on this subject) the information content of an utterance depends heavily on context and social convention, and which must be accounted for in generating or processing an utterance. The theory of locally complete information [ Etzioni et al. 1994 ] seems well suited to representing things like Gricean maxims, for example. To take a computer oriented example like the ones analyzed in that paper, if an agent lists three jobs in the print queue, it is implicitly telling you that those three jobs are the only three jobs in the queue, which is ....

Oren Etzioni, Keith Golden, and Dan Weld. Tractable Closed World Reasoning with Updates. In Proceedings, KR, May 1994.

....rely on a closed world assumption, that is they assume that domain model contains all information needed and that all unavailable information does not exist. On the contrary Internet Softbot [Etzioni and Weld, 1994] provides a framework to reason with incomplete information [Etzioni et al. 1992, Etzioni et al. 1994] executing sensing actions to provide forms of local closure, in other words to verify the actual presence of information in the source during plan execution. 5 Conclusion We conclude by stating that an intelligent access to information in the Web deeply relates to the representation of ....

Etzioni, O., Golden, K., and Weld, D. (1994). Tractable Closed World Reasoning with Updates. Proceedings of the Fourth International Conference on the Principles of Knowledge Representation and Reasoning (KR-94).

....query access plans. Shekhar (1989) developed an approach to trading off search time with execution time in optimizing query access plans. Both of these systems assume that the query access plans are given. Another planner that has been built for a information gathering task is the xii planner (Etzioni, Golden, Weld 1994). This planner serves as the query processor for the Unix Softbot (Etzioni Weld 1994) Compared to Sage, xii reasons about the information at a different level of granularity. Instead of representing general actions for manipulating data, each operator corresponds to a Unix command. The ....

....time in optimizing query access plans. Both of these systems assume that the query access plans are given. Another planner that has been built for a information gathering task is the xii planner (Etzioni, Golden, Weld 1994) This planner serves as the query processor for the Unix Softbot (Etzioni Weld 1994). Compared to Sage, xii reasons about the information at a different level of granularity. Instead of representing general actions for manipulating data, each operator corresponds to a Unix command. The advantage of their approach is that it provides finer grained control and reasoning of the ....

Etzioni, O.; Golden, K.; and Weld, D. 1994. Tractable closed-world reasoning with updates. In Fourth International Conference on Principles of Knowledge Representation and Reasoning.

....Manager is a specialized database that stores everything the Softbot has observed about the world. In order to support the XII planner, the model manager implements pattern directed queries via unification. The most novel aspect of the model manager is its capacity for local closed world reasoning [3]. Closed world reasoning the abilitytodraw conclusions based on the assumption that one knows about the existence of all relevant objects is essential for goal directed behavior [8] For example, when directed to find the cheapest direct flight, travel agents assume that after accessing ....

O. Etzioni, K. Golden, and D. Weld. Tractable closed-world reasoning with updates. In Proc. 4th Int. Conf. on Principles of Knowledge Representation and Reasoning, pages 178--189, June 1994.

....8 in the effects of ls, and since she knows the effects of ls, the agent can infer closed world knowledge. Such inference would be costly if it were done using first order theorem proving in the situation calculus. We have devised efficient algorithms for doing this reasoning, which we describe in [ 6, 8 ] . The translation of 8 effects into the situation calculus is straightforward (Other logical operators follow the same form) EFF(8 x:E; a; s) 8 x:EFF(E; a; s) 12) This definition of 8 effects may seem anticlimactic. The magic, however, stems from the way in which when introduces ....

Oren Etzioni, Keith Golden, and Dan Weld. Tractable closed-world reasoning with updates. In Proc. 4th Int. Conf. on Principles of Knowledge Representation and Reasoning, pages 178-- 189, 1994.

....a number of researchers have developed representations for encoding such judgments if they could be automatically pro A.Y. Levy, D.S. Weld Artificial Intelligence 118 (2000) 1 14 5 duced. A logical formulation of the (conditional or local) completeness of information sources is considered in [2,35,39,40,50,77,90], while a probabilistic formalism is developed in [45] For the most part, these papers focus on algorithms for choosing optimally between sources, leaving the construction of such resource descriptions as an open problem. Motro and Rakov s work [89] is an exception; they suggest a combined ....

....integration system in several ways. Most importantly, since a negative answer from a complete source is meaningful, the data integration system can prune access to other sources. The problem of describing completeness of Web sources and using this information for query processing is addressed in [2,35,39,40,50,77,90]. The work described in [45] describes a probabilistic formalism for describing the contents and overlaps among information sources, and presents algorithms for choosing optimally between sources. Differing query processing capabilities. From the perspective of the Web data integration system, ....

O. Etzioni, K. Golden, D. Weld, Tractable closed-world reasoning with updates, in: Proc. Fourth International Conference on Principles of Knowledge Representation and Reasoning (KR-94), Bonn, Germany, 1994, pp. 178--189.

....data. It seems that this topic is ripe for study, however, since a number of researchers have developed representations for encoding such judgments if they could be automatically produced. A logical formulation of the (conditional or local) completeness of information sources is considered in [91, 41, 39, 78, 35, 1, 51], while a probabilistic formalism is developed in [46] For the most part, these papers focus on algorithms for choosing optimally between sources, leaving the construction of such resource descriptions as an open problem. Motro and Rakov s work [90] is an exception; they suggest a combined manual ....

....since a negative 2 http: www.informatik.uni trier.de ley db 5 answer from a complete source is meaningful, the data integration system can prune access to other sources. The problem of describing completeness of web sources and using this information for query processing is addressed in [91, 41, 39, 78, 35, 1, 51]. The work described in [46] describes a probabilistic formalism for describing the contents and overlaps among information sources, and presents algorithms for choosing optimally between sources. Di ering query processing capabilities: From the perspective of the web data integration system, the ....

Oren Etzioni, Keith Golden, and Dan Weld. Tractable closed-world reasoning with updates. In Proceedings of the Fourth International Conference on Principles of Knowledge Representation and Reasoning, pages 178-189, 1994.

....involves satisfying the universal goal directly with a universal effect. The third method is to partition the universe to create two easier goals, and apply one of the three methods on each of the easier goals. The paper is organized as follows. Section 1 describes the xii algorithm. Sections 2, 3 and 4 describe the three mechanisms xii uses for satisfying universally quantified goals. Section 5 gives an example which illustrates the xii algorithm. Section 6 describes how LCW is represented in xii. Section 7 describes how LCW effects are compiled out of operator descriptions. Sections 8 and ....

....UNIX softbot the goal of printing all the files in papers, it can perform ls papers to get LCW on the contents of papers, and then print each file using lpr. The semantics and representation of LCW, as well as the mechanics of maintaining and updating D C , the LCW database, are discussed in [ 3 ] and we won t repeat them here. Instead we will focus on how the planner uses LCW to solve universally quantified goals, and how it generates new LCW sentences. 3 ucpop 2.0 does not assume a static universe. 3 3 Satisfying Universal Goals with Universal Effects The above technique of ....

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O. Etzioni, K. Golden, and D. Weld. Tractable closed-world reasoning with updates. In Proc. 4th Int. Conf. on Principles of Knowledge Representation and Reasoning, June 1994.

....to buy out of some questions, but forces us to address others. For example, sensors in the Internet domain are relatively noise free; thus, we do not concern ourselves with that issue. However, redundant sensing is an extremely important issue, and so we have developed a solution to this problem [13, 12]. xii is an extension of ucpop [38, 3] a partial order planner that handles universal quantification and conditional effects. In addition to the expressiveness of ucpop, xii supports the uwl [14] language for representing sensory actions and information goals. The combined action language, ....

O. Etzioni, K. Golden, and D. Weld. Tractable closed-world reasoning with updates. In Proc. 4th Int. Conf. on Principles of Knowledge Representation and Reasoning, pages 178--189, San Francisco, CA, June 1994. Morgan Kaufmann.

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Oren Etzioni, Keith Golden, and Daniel Weld. Tractable closed world reasoning with updates. In Proceedings of the 4th International Conference on Principles of Knowledge Representation and Reasoning, pages 178--189, San Francisco, CA, June 1994.

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O. Etzioni, K. Golden, and D. Weld. Tractable closed-world reasoning with updates. In Proceedings of the Fourth International Conference on Principles of Knowledge Representation and Reasoning, 1994.

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