53 research outputs found
End-to-End Differentiable Proving
We introduce neural networks for end-to-end differentiable proving of queries
to knowledge bases by operating on dense vector representations of symbols.
These neural networks are constructed recursively by taking inspiration from
the backward chaining algorithm as used in Prolog. Specifically, we replace
symbolic unification with a differentiable computation on vector
representations of symbols using a radial basis function kernel, thereby
combining symbolic reasoning with learning subsymbolic vector representations.
By using gradient descent, the resulting neural network can be trained to infer
facts from a given incomplete knowledge base. It learns to (i) place
representations of similar symbols in close proximity in a vector space, (ii)
make use of such similarities to prove queries, (iii) induce logical rules, and
(iv) use provided and induced logical rules for multi-hop reasoning. We
demonstrate that this architecture outperforms ComplEx, a state-of-the-art
neural link prediction model, on three out of four benchmark knowledge bases
while at the same time inducing interpretable function-free first-order logic
rules.Comment: NIPS 2017 camera-ready, NIPS 201
Combining Representation Learning with Logic for Language Processing
The current state-of-the-art in many natural language processing and
automated knowledge base completion tasks is held by representation learning
methods which learn distributed vector representations of symbols via
gradient-based optimization. They require little or no hand-crafted features,
thus avoiding the need for most preprocessing steps and task-specific
assumptions. However, in many cases representation learning requires a large
amount of annotated training data to generalize well to unseen data. Such
labeled training data is provided by human annotators who often use formal
logic as the language for specifying annotations. This thesis investigates
different combinations of representation learning methods with logic for
reducing the need for annotated training data, and for improving
generalization.Comment: PhD Thesis, University College London, Submitted and accepted in 201
Adversarial Sets for Regularising Neural Link Predictors
In adversarial training, a set of models learn together by pursuing competing
goals, usually defined on single data instances. However, in relational
learning and other non-i.i.d domains, goals can also be defined over sets of
instances. For example, a link predictor for the is-a relation needs to be
consistent with the transitivity property: if is-a(x_1, x_2) and is-a(x_2, x_3)
hold, is-a(x_1, x_3) needs to hold as well. Here we use such assumptions for
deriving an inconsistency loss, measuring the degree to which the model
violates the assumptions on an adversarially-generated set of examples. The
training objective is defined as a minimax problem, where an adversary finds
the most offending adversarial examples by maximising the inconsistency loss,
and the model is trained by jointly minimising a supervised loss and the
inconsistency loss on the adversarial examples. This yields the first method
that can use function-free Horn clauses (as in Datalog) to regularise any
neural link predictor, with complexity independent of the domain size. We show
that for several link prediction models, the optimisation problem faced by the
adversary has efficient closed-form solutions. Experiments on link prediction
benchmarks indicate that given suitable prior knowledge, our method can
significantly improve neural link predictors on all relevant metrics.Comment: Proceedings of the 33rd Conference on Uncertainty in Artificial
Intelligence (UAI), 201
TreeQN and ATreeC: Differentiable Tree-Structured Models for Deep Reinforcement Learning
Combining deep model-free reinforcement learning with on-line planning is a
promising approach to building on the successes of deep RL. On-line planning
with look-ahead trees has proven successful in environments where transition
models are known a priori. However, in complex environments where transition
models need to be learned from data, the deficiencies of learned models have
limited their utility for planning. To address these challenges, we propose
TreeQN, a differentiable, recursive, tree-structured model that serves as a
drop-in replacement for any value function network in deep RL with discrete
actions. TreeQN dynamically constructs a tree by recursively applying a
transition model in a learned abstract state space and then aggregating
predicted rewards and state-values using a tree backup to estimate Q-values. We
also propose ATreeC, an actor-critic variant that augments TreeQN with a
softmax layer to form a stochastic policy network. Both approaches are trained
end-to-end, such that the learned model is optimised for its actual use in the
tree. We show that TreeQN and ATreeC outperform n-step DQN and A2C on a
box-pushing task, as well as n-step DQN and value prediction networks (Oh et
al. 2017) on multiple Atari games. Furthermore, we present ablation studies
that demonstrate the effect of different auxiliary losses on learning
transition models
Programming with a Differentiable Forth Interpreter
Given that in practice training data is scarce for all but a small set of
problems, a core question is how to incorporate prior knowledge into a model.
In this paper, we consider the case of prior procedural knowledge for neural
networks, such as knowing how a program should traverse a sequence, but not
what local actions should be performed at each step. To this end, we present an
end-to-end differentiable interpreter for the programming language Forth which
enables programmers to write program sketches with slots that can be filled
with behaviour trained from program input-output data. We can optimise this
behaviour directly through gradient descent techniques on user-specified
objectives, and also integrate the program into any larger neural computation
graph. We show empirically that our interpreter is able to effectively leverage
different levels of prior program structure and learn complex behaviours such
as sequence sorting and addition. When connected to outputs of an LSTM and
trained jointly, our interpreter achieves state-of-the-art accuracy for
end-to-end reasoning about quantities expressed in natural language stories.Comment: 34th International Conference on Machine Learning (ICML 2017
RIDE: Rewarding Impact-Driven Exploration for Procedurally-Generated Environments
Exploration in sparse reward environments remains one of the key challenges
of model-free reinforcement learning. Instead of solely relying on extrinsic
rewards provided by the environment, many state-of-the-art methods use
intrinsic rewards to encourage exploration. However, we show that existing
methods fall short in procedurally-generated environments where an agent is
unlikely to visit a state more than once. We propose a novel type of intrinsic
reward which encourages the agent to take actions that lead to significant
changes in its learned state representation. We evaluate our method on multiple
challenging procedurally-generated tasks in MiniGrid, as well as on tasks with
high-dimensional observations used in prior work. Our experiments demonstrate
that this approach is more sample efficient than existing exploration methods,
particularly for procedurally-generated MiniGrid environments. Furthermore, we
analyze the learned behavior as well as the intrinsic reward received by our
agent. In contrast to previous approaches, our intrinsic reward does not
diminish during the course of training and it rewards the agent substantially
more for interacting with objects that it can control
e-SNLI: Natural Language Inference with Natural Language Explanations
In order for machine learning to garner widespread public adoption, models
must be able to provide interpretable and robust explanations for their
decisions, as well as learn from human-provided explanations at train time. In
this work, we extend the Stanford Natural Language Inference dataset with an
additional layer of human-annotated natural language explanations of the
entailment relations. We further implement models that incorporate these
explanations into their training process and output them at test time. We show
how our corpus of explanations, which we call e-SNLI, can be used for various
goals, such as obtaining full sentence justifications of a model's decisions,
improving universal sentence representations and transferring to out-of-domain
NLI datasets. Our dataset thus opens up a range of research directions for
using natural language explanations, both for improving models and for
asserting their trust.Comment: NeurIPS 201
Prioritized Level Replay
Environments with procedurally generated content serve as important
benchmarks for testing systematic generalization in deep reinforcement
learning. In this setting, each level is an algorithmically created environment
instance with a unique configuration of its factors of variation. Training on a
prespecified subset of levels allows for testing generalization to unseen
levels. What can be learned from a level depends on the current policy, yet
prior work defaults to uniform sampling of training levels independently of the
policy. We introduce Prioritized Level Replay (PLR), a general framework for
selectively sampling the next training level by prioritizing those with higher
estimated learning potential when revisited in the future. We show TD-errors
effectively estimate a level's future learning potential and, when used to
guide the sampling procedure, induce an emergent curriculum of increasingly
difficult levels. By adapting the sampling of training levels, PLR
significantly improves sample efficiency and generalization on Procgen
Benchmark--matching the previous state-of-the-art in test return--and readily
combines with other methods. Combined with the previous leading method, PLR
raises the state-of-the-art to over 76% improvement in test return relative to
standard RL baselines
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