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22
Dynamic Bayesian Networks: Representation, Inference and Learning
, 2002
"... Modelling sequential data is important in many areas of science and engineering. Hidden Markov models (HMMs) and Kalman filter models (KFMs) are popular for this because they are simple and flexible. For example, HMMs have been used for speech recognition and biosequence analysis, and KFMs have bee ..."
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Cited by 564 (3 self)
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Modelling sequential data is important in many areas of science and engineering. Hidden Markov models (HMMs) and Kalman filter models (KFMs) are popular for this because they are simple and flexible. For example, HMMs have been used for speech recognition and biosequence analysis, and KFMs have been used for problems ranging from tracking planes and missiles to predicting the economy. However, HMMs
and KFMs are limited in their “expressive power”. Dynamic Bayesian Networks (DBNs) generalize HMMs by allowing the state space to be represented in factored form, instead of as a single discrete random variable. DBNs generalize KFMs by allowing arbitrary probability distributions, not just (unimodal) linearGaussian. In this thesis, I will discuss how to represent many different kinds of models as DBNs, how to perform exact and approximate inference in DBNs, and how to learn DBN models from sequential data.
In particular, the main novel technical contributions of this thesis are as follows: a way of representing
Hierarchical HMMs as DBNs, which enables inference to be done in O(T) time instead of O(T 3), where T is the length of the sequence; an exact smoothing algorithm that takes O(log T) space instead of O(T); a simple way of using the junction tree algorithm for online inference in DBNs; new complexity bounds on exact online inference in DBNs; a new deterministic approximate inference algorithm called factored frontier; an analysis of the relationship between the BK algorithm and loopy belief propagation; a way of
applying RaoBlackwellised particle filtering to DBNs in general, and the SLAM (simultaneous localization
and mapping) problem in particular; a way of extending the structural EM algorithm to DBNs; and a variety of different applications of DBNs. However, perhaps the main value of the thesis is its catholic presentation of the field of sequential data modelling.
Scalable Techniques for Mining Causal Structures
 Data Mining and Knowledge Discovery
, 1998
"... Mining for association rules in market basket data has proved a fruitful area of research. Measures such as conditional probability (confidence) and correlation have been used to infer rules of the form "the existence of item A implies the existence of item B." However, such rules indicate only a st ..."
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Cited by 89 (1 self)
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Mining for association rules in market basket data has proved a fruitful area of research. Measures such as conditional probability (confidence) and correlation have been used to infer rules of the form "the existence of item A implies the existence of item B." However, such rules indicate only a statistical relationship between A and B. They do not specify the nature of the relationship: whether the presence of A causes the presence of B, or the converse, or some other attribute or phenomenon causes both to appear together. In applications, knowing such causal relationships is extremely useful for enhancing understanding and effecting change. While distinguishing causality from correlation is a truly difficult problem, recent work in statistics and Bayesian learning provide some avenues of attack. In these fields, the goal has generally been to learn complete causal models, which are essentially impossible to learn in largescale data mining applications with a large number of variab...
The role of Occam’s Razor in knowledge discovery
 Data Mining and Knowledge Discovery
, 1999
"... Abstract. Many KDD systems incorporate an implicit or explicit preference for simpler models, but this use of “Occam’s razor ” has been strongly criticized by several authors (e.g., Schaffer, 1993; Webb, 1996). This controversy arises partly because Occam’s razor has been interpreted in two quite di ..."
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Cited by 78 (3 self)
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Abstract. Many KDD systems incorporate an implicit or explicit preference for simpler models, but this use of “Occam’s razor ” has been strongly criticized by several authors (e.g., Schaffer, 1993; Webb, 1996). This controversy arises partly because Occam’s razor has been interpreted in two quite different ways. The first interpretation (simplicity is a goal in itself) is essentially correct, but is at heart a preference for more comprehensible models. The second interpretation (simplicity leads to greater accuracy) is much more problematic. A critical review of the theoretical arguments for and against it shows that it is unfounded as a universal principle, and demonstrably false. A review of empirical evidence shows that it also fails as a practical heuristic. This article argues that its continued use in KDD risks causing significant opportunities to be missed, and should therefore be restricted to the comparatively few applications where it is appropriate. The article proposes and reviews the use of domain constraints as an alternative for avoiding overfitting, and examines possible methods for handling the accuracy–comprehensibility tradeoff.
Answering “Whatif” Deployment and Configuration Questions with WISE
, 2008
"... Designers of content distribution networks often need to determine how changes to infrastructure deployment and configuration affect service response times when they deploy a new data center, change ISP peering, or change the mapping of clients to servers. Today, the designers use coarse, backofth ..."
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Cited by 29 (2 self)
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Designers of content distribution networks often need to determine how changes to infrastructure deployment and configuration affect service response times when they deploy a new data center, change ISP peering, or change the mapping of clients to servers. Today, the designers use coarse, backoftheenvelope calculations, or costly field deployments; they need better ways to evaluate the effects of such hypothetical “whatif ” questions before the actual deployments. This paper presents WhatIf Scenario Evaluator (WISE), a tool that predicts the effects of possible configuration and deployment changes in content distribution networks. WISE makes three contributions: (1) an algorithm that uses traces from existing deployments to learn causality among factors that affect service responsetime distributions; (2) an algorithm that uses the learned causal structure to estimate a dataset that is representative of the hypothetical scenario that a designer may wish to evaluate, and uses these datasets to predict future responsetime distributions; (3) a scenario specification language that allows a network designer to easily express hypothetical deployment scenarios without being cognizant of the dependencies between variables that affect service response times. Our evaluation, both in a controlled setting and in a realworld field deployment at a large, global CDN, shows that WISE can quickly and accurately predict service responsetime distributions for many practical whatif scenarios.
Modelling Activity Global Temporal Dependencies using Time Delayed Probabilistic Graphical Model
"... We present a novel approach for detecting global behaviour anomalies in multiple disjoint cameras by learning time delayed dependencies between activities cross camera views. Specifically, we propose to model multicamera activities using a Time Delayed Probabilistic Graphical Model (TDPGM) with di ..."
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Cited by 13 (2 self)
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We present a novel approach for detecting global behaviour anomalies in multiple disjoint cameras by learning time delayed dependencies between activities cross camera views. Specifically, we propose to model multicamera activities using a Time Delayed Probabilistic Graphical Model (TDPGM) with different nodes representing activities in different semantically decomposed regions from different camera views, and the directed links between nodes encoding causal relationships between the activities. A novel twostage structure learning algorithm is formulated to learn globally optimised timedelayed dependencies. A new cumulative abnormality score is also introduced to replace the conventional loglikelihood score for gaining significantly more robust and reliable realtime anomaly detection. The effectiveness of the proposed approach is validated using a camera network installed at a busy underground station. 1.
Robust independence testing for constraintbased learning of causal structure
 In UAI
, 2003
"... This paper considers a method that combines ideas from Bayesian learning, Bayesian network inference, and classical hypothesis testing to produce a more reliable and robust test of independence for constraintbased (CB) learning of causal structure. Our method produces a smoothed contingency table NX ..."
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Cited by 13 (1 self)
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This paper considers a method that combines ideas from Bayesian learning, Bayesian network inference, and classical hypothesis testing to produce a more reliable and robust test of independence for constraintbased (CB) learning of causal structure. Our method produces a smoothed contingency table NXY Z that can be used with any test of independence that relies on contingency table statistics. NXY Z can be calculated in the same asymptotic time and space required to calculate a standard contingency table, allows the specification of a prior distribution over parameters, and can be calculated when the database is incomplete. We provide theoretical justification for the procedure, and with synthetic data we demonstrate its benefits empirically over both a CB algorithm using the standard contingency table, and over a greedy Bayesian algorithm. We show that, even when used with noninformative priors, it results in better recovery of structural features and it produces networks with smaller KLDivergence, especially as the number of nodes increases or the number of records decreases. Another benefit is the dramatic reduction in the probability that a CB algorithm will stall during the search, providing a remedy for an annoying problem plaguing CB learning when the database is small. 1
An efficient data mining method for learning Bayesian networks using an evolutionary algorithmbased hybrid approach
, 2004
"... Abstract—Given the explosive growth of data collected from current business environment, data mining can potentially discover new knowledge to improve managerial decision making. This paper proposes a novel data mining approach that employs an evolutionary algorithm to discover knowledge represented ..."
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Cited by 5 (0 self)
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Abstract—Given the explosive growth of data collected from current business environment, data mining can potentially discover new knowledge to improve managerial decision making. This paper proposes a novel data mining approach that employs an evolutionary algorithm to discover knowledge represented in Bayesian networks. The approach is applied successfully to handle the business problem of finding response models from direct marketing data. Learning Bayesian networks from data is a difficult problem. There are two different approaches to the network learning problem. The first one uses dependency analysis, while the second one searches good network structures according to a metric. Unfortunately, both approaches have their own drawbacks. Thus, we propose a novel hybrid algorithm of the two approaches, which consists of two phases, namely, the conditional independence (CI) test and the search phases. In the CI test phase, dependency analysis is conducted to reduce the size of the search space. In the search phase, good Bayesian network models are generated by using an evolutionary algorithm. A new operator is introduced to further enhance the search effectiveness and efficiency. In a number of experiments and comparisons, the hybrid algorithm outperforms MDLEP, our previous algorithm which uses evolutionary programming (EP) for network learning, and other network learning algorithms. We then apply the approach to two data sets of direct marketing and compare the performance of the evolved Bayesian networks obtained by the new algorithm with those by MDLEP, the logistic regression models, the naïve Bayesian classifiers, and the treeaugmented naïve Bayesian network classifiers (TAN). In the comparison, the new algorithm outperforms the others. Index Terms—Bayesian networks, data mining, evolutionary computation, evolutionary programming (EP). I.
Some Variations on the PC Algorithm
"... This paper proposes some possible modifications on the PC basic learning algorithm and makes some experiments to study their behaviour. The variations are: to determine minimum size cut sets between two nodes to study the deletion of a link, to make statistical decisions taking into account a Bayesi ..."
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Cited by 4 (0 self)
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This paper proposes some possible modifications on the PC basic learning algorithm and makes some experiments to study their behaviour. The variations are: to determine minimum size cut sets between two nodes to study the deletion of a link, to make statistical decisions taking into account a Bayesian score instead of a classical Chisquare test, to study the refinement of the learned network by a greedy optimization of a Bayesian score, and to solve link ambiguities taking into account a measure of their strength. It will be shown that some of these modifications can improve PC performance, depending of the objective of the learning task: discovering the causal structure or approximating the joint probability distribution for the problem variables. 1
A KnowledgeIntensive Approach for SemiAutomatic Causal Subgroup Discovery
 In Proc. Workshop on Prior Conceptual Knowledge in Machine Learning and Knowledge Discovery (PriCKL’07), at the 18th European Conference on Machine Learning (ECML’07), 11th European Conference on Principles and Practice of Knowledge Discovery in Databases
, 2007
"... Abstract This paper presents a methodological view on knowledgeintensive causal subgroup discovery implemented in a semiautomatic approach. We show how to identify causal relations between subgroups by generating an extended causal subgroup network utilizing background knowledge. Using the links w ..."
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Cited by 3 (2 self)
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Abstract This paper presents a methodological view on knowledgeintensive causal subgroup discovery implemented in a semiautomatic approach. We show how to identify causal relations between subgroups by generating an extended causal subgroup network utilizing background knowledge. Using the links within the network we can identify causal relations, but also relations that are potentially confounded and/or effectmodified by external (confounding) factors. In a semiautomatic approach, the network and the discovered relations are presented to the user as an intuitive visualization. The applicability and benefit of the presented technique is illustrated by examples from a casestudy in the medical domain. 1