619 research outputs found
Characterizing Question Facets for Complex Answer Retrieval
Complex answer retrieval (CAR) is the process of retrieving answers to
questions that have multifaceted or nuanced answers. In this work, we present
two novel approaches for CAR based on the observation that question facets can
vary in utility: from structural (facets that can apply to many similar topics,
such as 'History') to topical (facets that are specific to the question's
topic, such as the 'Westward expansion' of the United States). We first explore
a way to incorporate facet utility into ranking models during query term score
combination. We then explore a general approach to reform the structure of
ranking models to aid in learning of facet utility in the query-document term
matching phase. When we use our techniques with a leading neural ranker on the
TREC CAR dataset, our methods rank first in the 2017 TREC CAR benchmark, and
yield up to 26% higher performance than the next best method.Comment: 4 pages; SIGIR 2018 Short Pape
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
Search Process as Transitions Between Neural States
Search is one of the most performed activities on the World Wide
Web. Various conceptual models postulate that the search process
can be broken down into distinct emotional and cognitive states
of searchers while they engage in a search process. These models
significantly contribute to our understanding of the search process.
However, they are typically based on self-report measures, such as
surveys, questionnaire, etc. and therefore, only indirectly monitor
the brain activity that supports such a process. With this work,
we take one step further and directly measure the brain activity
involved in a search process. To do so, we break down a search
process into five time periods: a realisation of Information Need,
Query Formulation, Query Submission, Relevance Judgment and
Satisfaction Judgment. We then investigate the brain activity between
these time periods. Using functional Magnetic Resonance
Imaging (fMRI), we monitored the brain activity of twenty-four participants
during a search process that involved answering questions
carefully selected from the TREC-8 and TREC 2001 Q/A Tracks.
This novel analysis that focuses on transitions rather than states
reveals the contrasting brain activity between time periods – which
enables the identification of the distinct parts of the search process
as the user moves through them. This work, therefore, provides an
important first step in representing the search process based on the
transitions between neural states. Discovering more precisely how
brain activity relates to different parts of the search process will
enable the development of brain-computer interactions that better
support search and search interactions, which we believe our study
and conclusions advance
Local and global query expansion for hierarchical complex topics
In this work we study local and global methods for query expansion for multifaceted complex topics. We study word-based and entity-based expansion methods and extend these approaches to complex topics using fine-grained expansion on different elements of the hierarchical query structure. For a source of hierarchical complex topics we use the TREC Complex Answer Retrieval (CAR) benchmark data collection. We find that leveraging the hierarchical topic structure is needed for both local and global expansion methods to be effective. Further, the results demonstrate that entity-based expansion methods show significant gains over word-based models alone, with local feedback providing the largest improvement. The results on the CAR paragraph retrieval task demonstrate that expansion models that incorporate both the hierarchical query structure and entity-based expansion result in a greater than 20% improvement over word-based expansion approaches
Explicit diversification of event aspects for temporal summarization
During major events, such as emergencies and disasters, a large volume of information is reported on newswire and social media platforms. Temporal summarization (TS) approaches are used to automatically produce concise overviews of such events by extracting text snippets from related articles over time. Current TS approaches rely on a combination of event relevance and textual novelty for snippet selection. However, for events that span multiple days, textual novelty is often a poor criterion for selecting snippets, since many snippets are textually unique but are semantically redundant or non-informative. In this article, we propose a framework for the diversification of snippets using explicit event aspects, building on recent works in search result diversification. In particular, we first propose two techniques to identify explicit aspects that a user might want to see covered in a summary for different types of event. We then extend a state-of-the-art explicit diversification framework to maximize the coverage of these aspects when selecting summary snippets for unseen events. Through experimentation over the TREC TS 2013, 2014, and 2015 datasets, we show that explicit diversification for temporal summarization significantly outperforms classical novelty-based diversification, as the use of explicit event aspects reduces the amount of redundant and off-topic snippets returned, while also increasing summary timeliness
Neural Vector Spaces for Unsupervised Information Retrieval
We propose the Neural Vector Space Model (NVSM), a method that learns
representations of documents in an unsupervised manner for news article
retrieval. In the NVSM paradigm, we learn low-dimensional representations of
words and documents from scratch using gradient descent and rank documents
according to their similarity with query representations that are composed from
word representations. We show that NVSM performs better at document ranking
than existing latent semantic vector space methods. The addition of NVSM to a
mixture of lexical language models and a state-of-the-art baseline vector space
model yields a statistically significant increase in retrieval effectiveness.
Consequently, NVSM adds a complementary relevance signal. Next to semantic
matching, we find that NVSM performs well in cases where lexical matching is
needed.
NVSM learns a notion of term specificity directly from the document
collection without feature engineering. We also show that NVSM learns
regularities related to Luhn significance. Finally, we give advice on how to
deploy NVSM in situations where model selection (e.g., cross-validation) is
infeasible. We find that an unsupervised ensemble of multiple models trained
with different hyperparameter values performs better than a single
cross-validated model. Therefore, NVSM can safely be used for ranking documents
without supervised relevance judgments.Comment: TOIS 201
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