A New Approach to Heuristic Estimations for Cost-Based Planning

AAAI Conferences

Solving relaxed problems is a commonly used technique in heuristic search to derive heuristic estimates. In heuristic planning, this is usually done by expanding a planning (reachability) graph on the current search state where the delete lists of operators are removed from their definition. Usually, this technique is used to obtain plan length estimates. However, in cost-based planning the goal is to find plans minimizing some criteria. This requires the redefinition of the heuristic estimation to account for operators costs. This paper introduces a new approach to compute cost-based heuristics using planning graphs in order to overcome some problems of the existing heuristics, together with a common way of characterizing heuristics based on planning graphs. We explore the heuristics behaviour in combination to two search algorithms. Results show that in some domains the new heuristics are adequate to obtain good quality plans without imposing significant overheads in running time.


Granger-causal Attentive Mixtures of Experts: Learning Important Features with Neural Networks

arXiv.org Artificial Intelligence

Knowledge of the importance of input features towards decisions made by machine-learning models is essential to increase our understanding of both the models and the underlying data. Here, we present a new approach to estimating feature importance with neural networks based on the idea of distributing the features of interest among experts in an attentive mixture of experts (AME). AMEs couple attentive gating networks with a Granger-causal objective to jointly produce accurate predictions as well as estimates of feature importance. Our experiments on an established benchmark and two real-world datasets show (i) that the feature importance estimates provided by AMEs compare favourably to those provided by state-of-the-art methods, (ii) that AMEs are significantly faster than existing methods, and (iii) that the associations discovered by AMEs are consistent with those reported by domain experts. In addition, we analyse the trade-off between predictive performance and estimation accuracy, the degree to which importance estimates of existing methods conform to predictive value, and whether a lower Granger-causal error on held-out data indicates a better feature importance estimation accuracy.


Building Contextual Anchor Text Representation using Graph Regularization

AAAI Conferences

Anchor texts are useful complementary description for target pages, widely applied to improve search relevance. The benefits come from the additional information introduced into document representation and the intelligent ways of estimating their relative importance. Previous work on anchor importance estimation treated anchor text independently without considering its context. As a result, the lack of constraints from such context fails to guarantee a stable anchor text representation. We propose an anchor graph regularization approach to incorporate constraints from such context into anchor text weighting process, casting the task into a convex quadratic optimization problem. The constraints draw from the estimation of anchor-anchor, anchor-page, and page-page similarity. Based on any estimators, our approach operates as a post process of refining the estimated anchor weights, making it a plug and play component in search infrastructure. Comparable experiments on standard data sets (TREC 2009 and 2010) demonstrate the efficacy of our approach.


Decentralized Cooperative Planning for Automated Vehicles with Continuous Monte Carlo Tree Search

arXiv.org Artificial Intelligence

Urban traffic scenarios often require a high degree of cooperation between traffic participants to ensure safety and efficiency. Observing the behavior of others, humans infer whether or not others are cooperating. This work aims to extend the capabilities of automated vehicles, enabling them to cooperate implicitly in heterogeneous environments. Continuous actions allow for arbitrary trajectories and hence are applicable to a much wider class of problems than existing cooperative approaches with discrete action spaces. Based on cooperative modeling of other agents, Monte Carlo Tree Search (MCTS) in conjunction with Decoupled-UCT evaluates the action-values of each agent in a cooperative and decentralized way, respecting the interdependence of actions among traffic participants. The extension to continuous action spaces is addressed by incorporating novel MCTS-specific enhancements for efficient search space exploration. The proposed algorithm is evaluated under different scenarios, showing that the algorithm is able to achieve effective cooperative planning and generate solutions egocentric planning fails to identify.


Estimating Node Importance in Knowledge Graphs Using Graph Neural Networks

arXiv.org Machine Learning

How can we estimate the importance of nodes in a knowledge graph (KG)? A KG is a multi-relational graph that has proven valuable for many tasks including question answering and semantic search. In this paper, we present GENI, a method for tackling the problem of estimating node importance in KGs, which enables several downstream applications such as item recommendation and resource allocation. While a number of approaches have been developed to address this problem for general graphs, they do not fully utilize information available in KGs, or lack flexibility needed to model complex relationship between entities and their importance. To address these limitations, we explore supervised machine learning algorithms. In particular, building upon recent advancement of graph neural networks (GNNs), we develop GENI, a GNN-based method designed to deal with distinctive challenges involved with predicting node importance in KGs. Our method performs an aggregation of importance scores instead of aggregating node embeddings via predicate-aware attention mechanism and flexible centrality adjustment. In our evaluation of GENI and existing methods on predicting node importance in real-world KGs with different characteristics, GENI achieves 5-17% higher NDCG@100 than the state of the art.