22,098 research outputs found
Ranked List Loss for Deep Metric Learning
The objective of deep metric learning (DML) is to learn embeddings that can
capture semantic similarity and dissimilarity information among data points.
Existing pairwise or tripletwise loss functions used in DML are known to suffer
from slow convergence due to a large proportion of trivial pairs or triplets as
the model improves. To improve this, ranking-motivated structured losses are
proposed recently to incorporate multiple examples and exploit the structured
information among them. They converge faster and achieve state-of-the-art
performance. In this work, we unveil two limitations of existing
ranking-motivated structured losses and propose a novel ranked list loss to
solve both of them. First, given a query, only a fraction of data points is
incorporated to build the similarity structure. Consequently, some useful
examples are ignored and the structure is less informative. To address this, we
propose to build a set-based similarity structure by exploiting all instances
in the gallery. The learning setting can be interpreted as few-shot retrieval:
given a mini-batch, every example is iteratively used as a query, and the rest
ones compose the gallery to search, i.e., the support set in few-shot setting.
The rest examples are split into a positive set and a negative set. For every
mini-batch, the learning objective of ranked list loss is to make the query
closer to the positive set than to the negative set by a margin. Second,
previous methods aim to pull positive pairs as close as possible in the
embedding space. As a result, the intraclass data distribution tends to be
extremely compressed. In contrast, we propose to learn a hypersphere for each
class in order to preserve useful similarity structure inside it, which
functions as regularisation. Extensive experiments demonstrate the superiority
of our proposal by comparing with the state-of-the-art methods.Comment: Accepted to T-PAMI. Therefore, to read the offical version, please go
to IEEE Xplore. Fine-grained image retrieval task. Our source code is
available online: https://github.com/XinshaoAmosWang/Ranked-List-Loss-for-DM
Training Curricula for Open Domain Answer Re-Ranking
In precision-oriented tasks like answer ranking, it is more important to rank
many relevant answers highly than to retrieve all relevant answers. It follows
that a good ranking strategy would be to learn how to identify the easiest
correct answers first (i.e., assign a high ranking score to answers that have
characteristics that usually indicate relevance, and a low ranking score to
those with characteristics that do not), before incorporating more complex
logic to handle difficult cases (e.g., semantic matching or reasoning). In this
work, we apply this idea to the training of neural answer rankers using
curriculum learning. We propose several heuristics to estimate the difficulty
of a given training sample. We show that the proposed heuristics can be used to
build a training curriculum that down-weights difficult samples early in the
training process. As the training process progresses, our approach gradually
shifts to weighting all samples equally, regardless of difficulty. We present a
comprehensive evaluation of our proposed idea on three answer ranking datasets.
Results show that our approach leads to superior performance of two leading
neural ranking architectures, namely BERT and ConvKNRM, using both pointwise
and pairwise losses. When applied to a BERT-based ranker, our method yields up
to a 4% improvement in MRR and a 9% improvement in P@1 (compared to the model
trained without a curriculum). This results in models that can achieve
comparable performance to more expensive state-of-the-art techniques.Comment: Accepted at SIGIR 2020 (long
Not All Dialogues are Created Equal: Instance Weighting for Neural Conversational Models
Neural conversational models require substantial amounts of dialogue data for
their parameter estimation and are therefore usually learned on large corpora
such as chat forums or movie subtitles. These corpora are, however, often
challenging to work with, notably due to their frequent lack of turn
segmentation and the presence of multiple references external to the dialogue
itself. This paper shows that these challenges can be mitigated by adding a
weighting model into the architecture. The weighting model, which is itself
estimated from dialogue data, associates each training example to a numerical
weight that reflects its intrinsic quality for dialogue modelling. At training
time, these sample weights are included into the empirical loss to be
minimised. Evaluation results on retrieval-based models trained on movie and TV
subtitles demonstrate that the inclusion of such a weighting model improves the
model performance on unsupervised metrics.Comment: Accepted to SIGDIAL 201
- …