Results 11  20
of
58
Rationality and intelligence
 Artificial Intelligence
, 1997
"... The longterm goal of our field is the creation and understanding of intelligence. Productive research in AI, both practical and theoretical, benefits from a notion of intelligence that is precise enough to allow the cumulative development of robust systems and general results. This paper outlines a ..."
Abstract

Cited by 79 (1 self)
 Add to MetaCart
The longterm goal of our field is the creation and understanding of intelligence. Productive research in AI, both practical and theoretical, benefits from a notion of intelligence that is precise enough to allow the cumulative development of robust systems and general results. This paper outlines a gradual evolution in our formal conception of intelligence that brings it closer to our informal conception and simultaneously reduces the gap between theory and practice. 1 Artificial Intelligence AI is a field in which the ultimate goal has often been somewhat illdefined and subject to dispute. Some researchers aim to emulate human cognition, others aim at the creation of
A Bayesian Approach to Causal Discovery
, 1997
"... We examine the Bayesian approach to the discovery of directed acyclic causal models and compare it to the constraintbased approach. Both approaches rely on the Causal Markov assumption, but the two differ significantly in theory and practice. An important difference between the approaches is that t ..."
Abstract

Cited by 79 (1 self)
 Add to MetaCart
We examine the Bayesian approach to the discovery of directed acyclic causal models and compare it to the constraintbased approach. Both approaches rely on the Causal Markov assumption, but the two differ significantly in theory and practice. An important difference between the approaches is that the constraintbased approach uses categorical information about conditionalindependence constraints in the domain, whereas the Bayesian approach weighs the degree to which such constraints hold. As a result, the Bayesian approach has three distinct advantages over its constraintbased counterpart. One, conclusions derived from the Bayesian approach are not susceptible to incorrect categorical decisions about independence facts that can occur with data sets of finite size. Two, using the Bayesian approach, finer distinctions among model structuresboth quantitative and qualitativecan be made. Three, information from several models can be combined to make better inferences and to better ...
Update rules for parameter estimation in Bayesian networks
, 1997
"... This paper reexamines the problem of parameter estimation in Bayesian networks with missing values and hidden variables from the perspective of recent work in online learning [12]. We provide a unified framework for parameter estimation that encompasses both online learning, where the model is co ..."
Abstract

Cited by 53 (2 self)
 Add to MetaCart
This paper reexamines the problem of parameter estimation in Bayesian networks with missing values and hidden variables from the perspective of recent work in online learning [12]. We provide a unified framework for parameter estimation that encompasses both online learning, where the model is continuously adapted to new data cases as they arrive, and the more traditional batch learning, where a preaccumulated set of samples is used in a onetime model selection process. In the batch case, our framework encompassesboth the gradient projection algorithm [2, 3] and the EM algorithm [14] for Bayesian networks. The framework also leads to new online and batch parameter update schemes, including a parameterized version of EM. We provide both empirical and theoretical results indicating that parameterized EM allows faster convergence to the maximum likelihood parameters than does standard EM. 1 Introduction Over the past few years, there has been a growing interest in the problem of le...
Learning Bayesian Nets that Perform Well
 In UAI97
, 1997
"... A Bayesian net (BN) is more than a succinct way to encode a probabilistic distribution; it also corresponds to a function used to answer queries. A BN can therefore be evaluated by the accuracy of the answers it returns. Many algorithms for learning BNs, however, attempt to optimize another criterio ..."
Abstract

Cited by 48 (17 self)
 Add to MetaCart
A Bayesian net (BN) is more than a succinct way to encode a probabilistic distribution; it also corresponds to a function used to answer queries. A BN can therefore be evaluated by the accuracy of the answers it returns. Many algorithms for learning BNs, however, attempt to optimize another criterion (usually likelihood, possibly augmented with a regularizing term), which is independent of the distribution of queries that are posed. This paper takes the "performance criteria" seriously, and considers the challenge of computing the BN whose performance  read "accuracy over the distribution of queries"  is optimal. We show that many aspects of this learning task are more difficult than the corresponding subtasks in the standard model. To appear in Proceedings of the Thirteenth Conference on Uncertainty in Artificial Intelligence (UAI97), Providence, RI, August 1997. 1 INTRODUCTION Many tasks require answering questions; this model applies, for example, to both expert systems th...
Sequential Update of Bayesian Network Structure
 In Proc. 13th Conference on Uncertainty in Artificial Intelligence (UAI’97
, 1997
"... There is an obvious need for improving the performance and accuracy of a Bayesian network as new data is observed. Because of errors in model construction and changes in the dynamics of the domains, we cannot afford to ignore the information in new data. While sequential update of parameters for a f ..."
Abstract

Cited by 47 (4 self)
 Add to MetaCart
There is an obvious need for improving the performance and accuracy of a Bayesian network as new data is observed. Because of errors in model construction and changes in the dynamics of the domains, we cannot afford to ignore the information in new data. While sequential update of parameters for a fixed structure can be accomplished using standard techniques, sequential update of network structure is still an open problem. In this paper, we investigate sequential update of Bayesian networks were both parameters and structure are expected to change. We introduce a new approach that allows for the flexible manipulation of the tradeoff between the quality of the learned networks and the amount of information that is maintained about past observations. We formally describe our approach including the necessary modifications to the scoring functions for learning Bayesian networks, evaluate its effectiveness through and empirical study, and extend it to the case of missing data. 1 Introductio...
Towards a Bayesian Model for Keyhole Plan Recognition in Large Domains
 In Proceedings of the Sixth International Conference on User Modeling
, 1997
"... . We present an approach to keyhole plan recognition which uses a Dynamic Belief Network to represent features of the domain that are needed to identify users' plans and goals. The structure of this network was determined from analysis of the domain. The conditional probability distributions are lea ..."
Abstract

Cited by 42 (3 self)
 Add to MetaCart
. We present an approach to keyhole plan recognition which uses a Dynamic Belief Network to represent features of the domain that are needed to identify users' plans and goals. The structure of this network was determined from analysis of the domain. The conditional probability distributions are learned during a training phase, which dynamically builds these probabilities from observations of user behaviour. This approach allows the use of incomplete, sparse and noisy data during both training and testing. We present experimental results of the application of our system to a MultiUser Dungeon adventure game with thousands of possible actions and positions. These results show a high degree of predictive accuracy and indicate that this approach will work in other domains with similar features. 1 Introduction To date, research in plan recognition has focused on three main areas: (1) inferring plans during cooperative interactions, (2) understanding stories, and (3) recognising the plans...
Learning Probabilistic Networks
 THE KNOWLEDGE ENGINEERING REVIEW
, 1998
"... A probabilistic network is a graphical model that encodes probabilistic relationships between variables of interest. Such a model records qualitative influences between variables in addition to the numerical parameters of the probability distribution. As such it provides an ideal form for combini ..."
Abstract

Cited by 36 (1 self)
 Add to MetaCart
A probabilistic network is a graphical model that encodes probabilistic relationships between variables of interest. Such a model records qualitative influences between variables in addition to the numerical parameters of the probability distribution. As such it provides an ideal form for combining prior knowledge, which might be limited solely to experience of the influences between some of the variables of interest, and data. In this paper, we first show how data can be used to revise initial estimates of the parameters of a model. We then progress to showing how the structure of the model can be revised as data is obtained. Techniques for learning with incomplete data are also covered.
Planning and control in stochastic domains with imperfect information
, 1997
"... Partially observable Markov decision processes (POMDPs) can be used to model complex control problems that include both action outcome uncertainty and imperfect observability. A control problem within the POMDP framework is expressed as a dynamic optimization problem with a value function that combi ..."
Abstract

Cited by 32 (6 self)
 Add to MetaCart
Partially observable Markov decision processes (POMDPs) can be used to model complex control problems that include both action outcome uncertainty and imperfect observability. A control problem within the POMDP framework is expressed as a dynamic optimization problem with a value function that combines costs or rewards from multiple steps. Although the POMDP framework is more expressive than other simpler frameworks, like Markov decision processes (MDP), its associated optimization methods are more demanding computationally and only very small problems can be solved exactly in practice. Our work focuses on two possible approaches that can be used to solve larger problems: approximation methods and exploitation of additional problem structure. First, a number of new eÆcient approximation methods and improvements of existing algorithms are proposed. These include (1) the fast informed bound method based on approximate dynamic programming updates that lead to piecewise linear and convex v...
When do Numbers Really Matter?
 Journal of Artificial Intelligence Research
, 2002
"... Common wisdom has it that small distinctions in the probabilities (parameters) quantifying a belief network do not matter much for the results of probabilistic queries. Yet, one can develop realistic scenarios under which small variations in network parameters can lead to significant changes in c ..."
Abstract

Cited by 28 (6 self)
 Add to MetaCart
Common wisdom has it that small distinctions in the probabilities (parameters) quantifying a belief network do not matter much for the results of probabilistic queries. Yet, one can develop realistic scenarios under which small variations in network parameters can lead to significant changes in computed queries. A pending theoretical question is then to analytically characterize parameter changes that do or do not matter. In this paper, we study the sensitivity of probabilistic queries to changes in network parameters and prove some tight bounds on the impact that such parameters can have on queries. Our analytic results pinpoint some interesting situations under which parameter changes do or do not matter. These results are important for knowledge engineers as they help them identify influential network parameters. They also help explain some of the previous experimental results and observations with regards to network robustness against parameter changes.
Accelerated Quantification of Bayesian Networks with Incomplete Data
 In Proceedings of First International Conference on Knowledge Discovery and Data Mining
, 1995
"... Probabilistic expert systems based on Bayesian networks (BNs) require initial specification of both a qualitative graphical structure and quantitative assessment of conditional probability tables. This paper considers statistical batch learning of the probability tables on the basis of incomple ..."
Abstract

Cited by 28 (2 self)
 Add to MetaCart
Probabilistic expert systems based on Bayesian networks (BNs) require initial specification of both a qualitative graphical structure and quantitative assessment of conditional probability tables. This paper considers statistical batch learning of the probability tables on the basis of incomplete data and expert knowledge. The EM algorithm with a generalized conjugate gradient acceleration method has been dedicated to quantification of BNs by maximum posterior likelihood estimation for a superclass of the recursive graphical models. This new class of models allows a great variety of local functional restrictions to be imposed on the statistical model, which hereby extents the control and applicability of the constructed method for quantifying BNs. Introduction The construction of probabilistic expert systems (Pearl 1988, Andreassen et al. 1989) based on Bayesian networks (BNs) is often a challenging process. It is typically divided into two parts: First the constructi...