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Title: DuoRC: Towards Complex Language Understanding with Paraphrased Reading Comprehension

Paper content:
We propose DuoRC, a novel dataset for Reading Comprehension (RC) that motivates several new challenges for neural approaches in language understanding beyond those offered by existing RC datasets.
DuoRC contains 186,089 unique question-answer pairs created from a collection of 7680 pairs of movie plots where each pair in the collection reflects two versions of the same movie - one from Wikipedia and the other from IMDb - written by two different authors.
We asked crowdsourced workers to create questions from one version of the plot and a different set of workers to extract or synthesize corresponding answers from the other version.
This unique characteristic of DuoRC where questions and answers are created from different versions of a document narrating the same underlying story, ensures by design, that there is very little lexical overlap between the questions created from one version and the segments containing the answer in the other version.
Further, since the two versions have different level of plot detail, narration style, vocabulary, etc., answering questions from the second version requires deeper language understanding and incorporating background knowledge not available in the given text.
Additionally, the narrative style of passages arising from movie plots (as opposed to typical descriptive passages in existing datasets) exhibits the need to perform complex reasoning over events across multiple sentences.
Indeed, we observe that state-of-the-art neural RC models which have achieved near human performance on the SQuAD dataset, even when coupled with traditional NLP techniques to address the challenges presented in DuoRC exhibit very poor performance (F1 score of 37.42% on DuoRC v/s 86% on SQuAD dataset).
This opens up several interesting research avenues wherein DuoRC could complement other Reading Comprehension style datasets to explore novel neural approaches for studying language understanding.
Natural Language Understanding is widely accepted to be one of the key capabilities required for AI systems.
Scientific progress on this endeavor is measured through multiple tasks such as machine translation, reading comprehension, question-answering, and others, each of which requires the machine to demonstrate the ability to "comprehend" the given textual input (apart from other aspects) and achieve their task-specific goals.
In particular, Reading Comprehension (RC) systems are required to "understand" a given text passage as input and then answer questions based on it.
It is therefore critical, that the dataset benchmarks established for the RC task keep progressing in complexity to reflect the challenges that arise in true language understanding, thereby enabling the development of models and techniques to solve these challenges.For RC in particular, there has been significant progress over the recent years with several benchmark datasets, the most popular of which are the SQuAD dataset BID11 , TriviaQA BID4 , MS MARCO BID8 , MovieQA BID16 and cloze-style datasets BID6 BID9 BID2 .
However, these benchmarks, owing to both the nature of the passages and the question-answer pairs to evaluate the RC task, have 2 primary limitations in studying language understanding:
(i) Other than MovieQA, which is a small dataset of 15K QA pairs, all other large-scale RC datasets deal only with factual descriptive passages and not narratives (involving events with causality linkages that require reasoning and background knowledge) which is the case with a lot of real-world content such as story books, movies, news reports, etc.
(ii) their questions possess a large lexical overlap with segments of the passage, or have a high noise level in Q/A pairs themselves.
As demonstrated by recent work, this makes it easy for even simple keyword matching algorithms to achieve high accuracy BID19 .
In fact, these models have been shown to perform poorly in the presence of adversarially inserted sentences which have a high word overlap with the question but do not contain the answer BID3 .
While this problem does not exist in TriviaQA it is admittedly noisy because of the use of distant supervision.
Similarly, for cloze-style datasets, due to the automatic question generation process, it is very easy for current models to reach near human performance BID1 .
This therefore limits the complexity in language understanding that a machine is required to demonstrate to do well on the RC task.Motivated by these shortcomings and to push the state-of-the-art in language understanding in RC, in this paper we propose DuoRC, which specifically presents the following challenges beyond the existing datasets:1.
DuoRC is especially designed to contain a large number of questions with low lexical overlap between questions and their corresponding passages.2.
It requires the use of background and common-sense knowledge to arrive at the answer and go beyond the content of the passage itself.3.
It contains narrative passages from movie plots that require complex reasoning across multiple sentences to infer the answer.4.
Several of the questions in DuoRC, while seeming relevant, cannot actually be answered from the given passage, thereby requiring the machine to detect the unanswerability of questions.In order to capture these four challenges, DuoRC contains QA pairs created from pairs of documents describing movie plots which were gathered as follows.
Each document in a pair is a different version of the same movie plot written by different authors; one version of the plot is taken from the Wikipedia page of the movie whereas the other from its IMDb page (see FIG0 for portions of an example pair of plots from the movie "Twelve Monkeys").
We first showed crowd workers on Amazon Mechanical Turk (AMT) the first version of the plot and asked them to create QA pairs from it.
We then showed the second version of the plot along with the questions created from the first version to a different set of workers on AMT and asked them to provide answers by reading the second version only.
Since the two versions contain different levels of plot detail, narration style, vocabulary, etc., answering questions from the second version exhibits all of the four challenges mentioned above.We now make several interesting observations from the example in FIG0 .
For 4 out of the 8 questions (Q1, Q2, Q4, and Q7), though the answers extracted from the two plots are exactly the same, the analysis required to arrive at this answer is very different in the two cases.
In particular, for Q1 even though there is no explicit mention of the prisoner living in a subterranean shelter and hence no lexical overlap with the question, the workers were still able to infer that the answer is Philadelphia because that is the city to which James Cole travels to for his mission.
Another interesting characteristic of this dataset is that for a few questions (Q6, Q8) alternative but valid answers are obtained from the second plot.
Further, note the kind of complex reasoning required for answering Q8 where the machine needs to resolve coreferences over multiple sentences (that man refers to Dr. Peters) and use common sense knowledge that if an item clears an airport screening, then a person can likely board the plane with it.
To re-emphasize, these examples exhibit the need for machines to demonstrate new capabilities in RC such as:
(i) employing a knowledge graph (e.g. to know that Philadelphia is a city in Q1),
(ii) common-sense knowledge (e.g., clearing airport security implies boarding)
(iii) paraphrase/semantic understanding (e.g. revolver is a type of handgun in Q7)
(iv) multiple-sentence inferencing across events in the passage including coreference resolution of named entities and nouns, and
(v) educated guesswork when the question is not directly answerable but there are subtle hints in the passage (as in Q1).
Finally, for quite a few questions, there wasn't sufficient information in the second plot to obtain their answers.
In such cases, the workers marked the question as "unanswerable".
This brings out a very important challenge for machines to exhibit (i.e. detect unanswerability of questions) because a practical system should be able to know when it is not possible for it to answer a particular question given the data available to it, and in such cases, possibly delegate the task to a human instead.Current RC systems built using existing datasets are far from possessing these capabilities to solve the above challenges.
In Section 4, we seek to establish solid baselines for DuoRC employing state-of-the-art RC models coupled with a collection of standard NLP techniques to address few of the above challenges.
Proposing novel neural models that solve all of the challenges in DuoRC is out of the scope of this paper.
Our experiments demonstrate that when the existing state-of-the-art RC systems are trained and evaluated on DuoRC they perform poorly leaving a lot of scope for improvement and open new avenues for research in RC.
Do note that this dataset is not a substitute for existing RC datasets but can be coupled with them to collectively address a large set of challenges in language understanding with RC (the more the merrier).
The results of our experiments are summarized in TAB3 which we discuss in the following sub-sections.
• SpanModel v/s GenModel: Comparing the first two rows (SelfRC) and the last two rows (ParaphraseRC) of TAB4 we see that the SpanModel clearly outperforms the GenModel.
This is not very surprising for two reasons.
First, around 70% (and 50%) of the answers in SelfRC (and ParaphraseRC) respectively, match an exact span in the document so the span based model still has scope to do well on these answers.
On the other hand, even if the first stage of the GenModel predicts the span correctly, the second stage could make an error in generating the correct answer from it because generation is a harder problem.
For the second stage, it is expected that the GenModel should learn to copy the predicted span to produce the answer output (as is required in most cases) and only occasionally where necessary, generate an answer.
However, surprisingly the GenModel fails to even do this.
Manual inspection of the generated answers shows that in many cases the generator ends up generating either more or fewer words compared the true answer.
This demonstrates that there is clearly scope for the GenModel to perform better.•
SelfRC v/s ParaphraseRC: Comparing the SelfRC and ParaphraseRC numbers in TAB4 , we observe that the performance of the models clearly drops for the latter task, thus validating our hypothesis that ParaphraseRC is a indeed a much harder task.•
Effect of NLP pre-processing: As mentioned in Section 4, for ParaphraseRC, we first perform a few pre-processing steps to identify relevant sentences in the longer document. In
order to evaluate whether the pre-processing method is effective, we compute: (i
) the percentage of the document that gets pruned, and (
ii) whether the true answer is present in the pruned document (i.e., average recall of the answer).
We can compute the recall only for the span-based subset of the data since for the remaining data we do not know the true span.
In TAB3 , we report these two quantities for the span-based subset using different pruning strategies.
Finally, comparing the SpanModel with and without Paraphrasing in TAB4 for ParaphraseRC, we observe that the pre-processing step indeed improves the performance of the Span Detection Model.•
Effect of oracle pre-processing: As noted in Section 3, the ParaphraseRC plot is almost double in length in comparison to the SelfRC plot, which while adding to the complexities of the former task, is clearly not the primary reason of the model's poor performance on that. To
empirically validate this, we perform an Oracle pre-processing step, where, starting with the knowledge of the span containing the true answer, we extract a subplot around it such that the span is randomly located within that subplot and the average length of the subplot is similar to the SelfRC plots. The
SpanModel with this Oracle preprocessed data exhibits a minor improvement in performance over that with rule-based preprocessing (1.6% in Accuracy and 4.3% in F1 over the Span Test), still failing to bridge the wide performance gap between the SelfRC and ParaphraseRC task.• Cross
Testing We wanted to examine whether a model trained on SelfRC performs well on ParaphraseRC and vice-versa. We also
wanted to evaluate if merging the two datasets improves the performance of the model. For this
we experimented with various combinations of train and test data. The results
of these experiments for the SpanModel are summarized in TAB5 . We make two
main observations. First, training
on one dataset and evaluating on the other results in a drop in the performance. Merging the training
data from the two datasets exhibits better performance on the individual test sets.Based on our experiments and empirical observations we believe that the DuoRC dataset indeed holds a lot of potential for advancing the horizon of complex language understanding by exposing newer challenges in this area.
In this paper we introduced DuoRC, a large scale RC dataset of 186K human-generated questionanswer pairs created from 7680 pairs of parallel movie-plots, each pair taken from Wikipedia and IMDb.
We then showed that this dataset, by design, ensures very little or no lexical overlap between the questions created from one version and the segments containing the answer in the other version.
With this, we hope to introduce the RC community to new research challenges on question-answering requiring external knowledge and common-sense driven reasoning, deeper language understanding and multiple-sentence inferencing.
Through our experiments, we show how the state-of-the-art RC models, which have achieved near human performance on the SQuAD dataset, perform poorly on our dataset, thus emphasizing the need to explore further avenues for research.

assistant: text: We propose DuoRC, a novel dataset for Reading Comprehension (RC) containing 186,089 human-generated QA pairs created from a collection of 7680 pairs of parallel movie plots and introduce a RC task of reading one version of the plot and answering questions created from the other version; thus by design, requiring complex reasoning and deeper language understanding to overcome the poor lexical overlap between the plot and the question.