prompt_front: You are given a scientific article and a question. Answer the question as concisely as you can, using a single phrase or sentence if possible. If the question cannot be answered based on the information in the article, write "unanswerable". If the question is a yes/no question, answer "yes", "no", or "unanswerable". Do not provide any explanation.

Please answer the questions based on the text provided below. What type of evaluation is proposed for this task?
Context 1: Introduction
Multi-document summarization (MDS), the transformation of a set of documents into a short text containing their most important aspects, is a long-studied problem in NLP  Generated summaries have been shown to support humans dealing with large document collections in information seeking tasks BIBREF0 , BIBREF1 , BIBREF2   However, when exploring a set of documents manually, humans rarely write a fully-formulated summary for themselves  Instead, user studies BIBREF3 , BIBREF4 show that they note down important keywords and phrases, try to identify relationships between them and organize them accordingly  Therefore, we believe that the study of summarization with similarly structured outputs is an important extension of the traditional task 
A representation that is more in line with observed user behavior is a concept map BIBREF5 , a labeled graph showing concepts as nodes and relationships between them as edges (Figure FIGREF2 )  Introduced in 1972 as a teaching tool BIBREF6 , concept maps have found many applications in education BIBREF7 , BIBREF8 , for writing assistance BIBREF9 or to structure information repositories BIBREF10 , BIBREF11   For summarization, concept maps make it possible to represent a summary concisely and clearly reveal relationships  Moreover, we see a second interesting use case that goes beyond the capabilities of textual summaries: When concepts and relations are linked to corresponding locations in the documents they have been extracted from, the graph can be used to navigate in a document collection, similar to a table of contents  An implementation of this idea has been recently described by BIBREF12  
The corresponding task that we propose is concept-map-based MDS, the summarization of a document cluster in the form of a concept map  In order to develop and evaluate methods for the task, gold-standard corpora are necessary, but no suitable corpus is available  The manual creation of such a dataset is very time-consuming, as the annotation includes many subtasks  In particular, an annotator would need to manually identify all concepts in the documents, while only a few of them will eventually end up in the summary 
To overcome these issues, we present a corpus creation method that effectively combines automatic preprocessing, scalable crowdsourcing and high-quality expert annotations  Using it, we can avoid the high effort for single annotators, allowing us to scale to document clusters that are 15 times larger than in traditional summarization corpora  We created a new corpus of 30 topics, each with around 40 source documents on educational topics and a summarizing concept map that is the consensus of many crowdworkers (see Figure FIGREF3 ) 
As a crucial step of the corpus creation, we developed a new crowdsourcing scheme called low-context importance annotation  In contrast to traditional approaches, it allows us to determine important elements in a document cluster without requiring annotators to read all documents, making it feasible to crowdsource the task and overcome quality issues observed in previous work BIBREF13   We show that the approach creates reliable data for our focused summarization scenario and, when tested on traditional summarization corpora, creates annotations that are similar to those obtained by earlier efforts 
To summarize, we make the following contributions: (1) We propose a novel task, concept-map-based MDS (§ SECREF2 ), (2) present a new crowdsourcing scheme to create reference summaries (§ SECREF4 ), (3) publish a new dataset for the proposed task (§ SECREF5 ) and (4) provide an evaluation protocol and baseline (§ SECREF7 )  We make these resources publicly available under a permissive license 
Task
Concept-map-based MDS is defined as follows: Given a set of related documents, create a concept map that represents its most important content, satisfies a specified size limit and is connected 
We define a concept map as a labeled graph showing concepts as nodes and relationships between them as edges  Labels are arbitrary sequences of tokens taken from the documents, making the summarization task extractive  A concept can be an entity, abstract idea, event or activity, designated by its unique label  Good maps should be propositionally coherent, meaning that every relation together with the two connected concepts form a meaningful proposition 
The task is complex, consisting of several interdependent subtasks  One has to extract appropriate labels for concepts and relations and recognize different expressions that refer to the same concept across multiple documents  Further, one has to select the most important concepts and relations for the summary and finally organize them in a graph satisfying the connectedness and size constraints 
Related Work
Some attempts have been made to automatically construct concept maps from text, working with either single documents BIBREF14 , BIBREF9 , BIBREF15 , BIBREF16 or document clusters BIBREF17 , BIBREF18 , BIBREF19   These approaches extract concept and relation labels from syntactic structures and connect them to build a concept map  However, common task definitions and comparable evaluations are missing  In addition, only a few of them, namely Villalon 2012 and Valerio 2006, define summarization as their goal and try to compress the input to a substantially smaller size  Our newly proposed task and the created large-cluster dataset fill these gaps as they emphasize the summarization aspect of the task 
For the subtask of selecting summary-worthy concepts and relations, techniques developed for traditional summarization BIBREF20 and keyphrase extraction BIBREF21 are related and applicable  Approaches that build graphs of propositions to create a summary BIBREF22 , BIBREF23 , BIBREF24 , BIBREF25 seem to be particularly related, however, there is one important difference: While they use graphs as an intermediate representation from which a textual summary is then generated, the goal of the proposed task is to create a graph that is directly interpretable and useful for a user  In contrast, these intermediate graphs, e g  AMR, are hardly useful for a typical, non-linguist user 
For traditional summarization, the most well-known datasets emerged out of the DUC and TAC competitions  They provide clusters of news articles with gold-standard summaries  Extending these efforts, several more specialized corpora have been created: With regard to size, Nakano 2010 present a corpus of summaries for large-scale collections of web pages  Recently, corpora with more heterogeneous documents have been suggested, e g  BIBREF26 and BIBREF27   The corpus we present combines these aspects, as it has large clusters of heterogeneous documents, and provides a necessary benchmark to evaluate the proposed task 
For concept map generation, one corpus with human-created summary concept maps for student essays has been created BIBREF28   In contrast to our corpus, it only deals with single documents, requires a two orders of magnitude smaller amount of compression of the input and is not publicly available  
Other types of information representation that also model concepts and their relationships are knowledge bases, such as Freebase BIBREF29 , and ontologies  However, they both differ in important aspects: Whereas concept maps follow an open label paradigm and are meant to be interpretable by humans, knowledge bases and ontologies are usually more strictly typed and made to be machine-readable  Moreover, approaches to automatically construct them from text typically try to extract as much information as possible, while we want to summarize a document 
Low-Context Importance Annotation
Lloret 2013 describe several experiments to crowdsource reference summaries  Workers are asked to read 10 documents and then select 10 summary sentences from them for a reward of $0 05  They discovered several challenges, including poor work quality and the subjectiveness of the annotation task, indicating that crowdsourcing is not useful for this purpose 
To overcome these issues, we introduce a new task design, low-context importance annotation, to determine summary-worthy parts of documents  Compared to Lloret et al 's approach, it is more in line with crowdsourcing best practices, as the tasks are simple, intuitive and small BIBREF30 and workers receive reasonable payment BIBREF31   Most importantly, it is also much more efficient and scalable, as it does not require workers to read all documents in a cluster 
Task Design
We break down the task of importance annotation to the level of single propositions  The goal of our crowdsourcing scheme is to obtain a score for each proposition indicating its importance in a document cluster, such that a ranking according to the score would reveal what is most important and should be included in a summary  In contrast to other work, we do not show the documents to the workers at all, but provide only a description of the document cluster's topic along with the propositions  This ensures that tasks are small, simple and can be done quickly (see Figure FIGREF4 ) 
In preliminary tests, we found that this design, despite the minimal context, works reasonably on our focused clusters on common educational topics  For instance, consider Figure FIGREF4 : One can easily say that P1 is more important than P2 without reading the documents 
We distinguish two task variants:
Instead of enforcing binary importance decisions, we use a 5-point Likert-scale to allow more fine-grained annotations  The obtained labels are translated into scores (5  1) and the average of all scores for a proposition is used as an estimate for its importance  This follows the idea that while single workers might find the task subjective, the consensus of multiple workers, represented in the average score, tends to be less subjective due to the “wisdom of the crowd”  We randomly group five propositions into a task 
As an alternative, we use a second task design based on pairwise comparisons  Comparisons are known to be easier to make and more consistent BIBREF32 , but also more expensive, as the number of pairs grows quadratically with the number of objects  To reduce the cost, we group five propositions into a task and ask workers to order them by importance per drag-and-drop  From the results, we derive pairwise comparisons and use TrueSkill BIBREF35 , a powerful Bayesian rank induction model BIBREF34 , to obtain importance estimates for each proposition 
Pilot Study
To verify the proposed approach, we conducted a pilot study on Amazon Mechanical Turk using data from TAC2008 BIBREF36   We collected importance estimates for 474 propositions extracted from the first three clusters using both task designs  Each Likert-scale task was assigned to 5 different workers and awarded $0 06  For comparison tasks, we also collected 5 labels each, paid $0 05 and sampled around 7% of all possible pairs  We submitted them in batches of 100 pairs and selected pairs for subsequent batches based on the confidence of the TrueSkill model 
Following the observations of Lloret 2013, we established several measures for quality control  First, we restricted our tasks to workers from the US with an approval rate of at least 95%  Second, we identified low quality workers by measuring the correlation of each worker's Likert-scores with the average of the other four scores  The worst workers (at most 5% of all labels) were removed 
In addition, we included trap sentences, similar as in BIBREF13 , in around 80 of the tasks  In contrast to Lloret et al 's findings, both an obvious trap sentence (This sentence is not important) and a less obvious but unimportant one (Barack Obama graduated from Harvard Law) were consistently labeled as unimportant (1 08 and 1 14), indicating that the workers did the task properly 
For Likert-scale tasks, we follow Snow 2008 and calculate agreement as the average Pearson correlation of a worker's Likert-score with the average score of the remaining workers  This measure is less strict than exact label agreement and can account for close labels and high- or low-scoring workers  We observe a correlation of 0 81, indicating substantial agreement  For comparisons, the majority agreement is 0 73  To further examine the reliability of the collected data, we followed the approach of Kiritchenko 2016 and simply repeated the crowdsourcing for one of the three topics  Between the importance estimates calculated from the first and second run, we found a Pearson correlation of 0 82 (Spearman 0 78) for Likert-scale tasks and 0 69 (Spearman 0 66) for comparison tasks  This shows that the approach, despite the subjectiveness of the task, allows us to collect reliable annotations 
In addition to the reliability studies, we extrinsically evaluated the annotations in the task of summary evaluation  For each of the 58 peer summaries in TAC2008, we calculated a score as the sum of the importance estimates of the propositions it contains  Table TABREF13 shows how these peer scores, averaged over the three topics, correlate with the manual responsiveness scores assigned during TAC in comparison to ROUGE-2 and Pyramid scores  The results demonstrate that with both task designs, we obtain importance annotations that are similarly useful for summary evaluation as pyramid annotations or gold-standard summaries (used for ROUGE) 
Based on the pilot study, we conclude that the proposed crowdsourcing scheme allows us to obtain proper importance annotations for propositions  As workers are not required to read all documents, the annotation is much more efficient and scalable as with traditional methods 
Corpus Creation
This section presents the corpus construction process, as outlined in Figure FIGREF16 , combining automatic preprocessing, scalable crowdsourcing and high-quality expert annotations to be able to scale to the size of our document clusters  For every topic, we spent about $150 on crowdsourcing and 1 5h of expert annotations, while just a single annotator would already need over 8 hours (at 200 words per minute) to read all documents of a topic 
Source Data
As a starting point, we used the DIP corpus BIBREF37 , a collection of 49 clusters of 100 web pages on educational topics (e g  bullying, homeschooling, drugs) with a short description of each topic  It was created from a large web crawl using state-of-the-art information retrieval  We selected 30 of the topics for which we created the necessary concept map annotations 
Proposition Extraction
As concept maps consist of propositions expressing the relation between concepts (see Figure FIGREF2 ), we need to impose such a structure upon the plain text in the document clusters  This could be done by manually annotating spans representing concepts and relations, however, the size of our clusters makes this a huge effort: 2288 sentences per topic (69k in total) need to be processed  Therefore, we resort to an automatic approach 
The Open Information Extraction paradigm BIBREF38 offers a representation very similar to the desired one  For instance, from
Students with bad credit history should not lose hope and apply for federal loans with the FAFSA 
Open IE systems extract tuples of two arguments and a relation phrase representing propositions:
(s  with bad credit history, should not lose, hope)
(s  with bad credit history, apply for, federal loans with the FAFSA)
While the relation phrase is similar to a relation in a concept map, many arguments in these tuples represent useful concepts  We used Open IE 4, a state-of-the-art system BIBREF39 to process all sentences  After removing duplicates, we obtained 4137 tuples per topic 
Since we want to create a gold-standard corpus, we have to ensure that we produce high-quality data  We therefore made use of the confidence assigned to every extracted tuple to filter out low quality ones  To ensure that we do not filter too aggressively (and miss important aspects in the final summary), we manually annotated 500 tuples sampled from all topics for correctness  On the first 250 of them, we tuned the filter threshold to 0 5, which keeps 98 7% of the correct extractions in the unseen second half  After filtering, a topic had on average 2850 propositions (85k in total) 
Proposition Filtering
Despite the similarity of the Open IE paradigm, not every extracted tuple is a suitable proposition for a concept map  To reduce the effort in the subsequent steps, we therefore want to filter out unsuitable ones  A tuple is suitable if it (1) is a correct extraction, (2) is meaningful without any context and (3) has arguments that represent proper concepts  We created a guideline explaining when to label a tuple as suitable for a concept map and performed a small annotation study  Three annotators independently labeled 500 randomly sampled tuples  The agreement was 82% ( INLINEFORM0 )  We found tuples to be unsuitable mostly because they had unresolvable pronouns, conflicting with (2), or arguments that were full clauses or propositions, conflicting with (3), while (1) was mostly taken care of by the confidence filtering in § SECREF21  
Due to the high number of tuples we decided to automate the filtering step  We trained a linear SVM on the majority voted annotations  As features, we used the extraction confidence, length of arguments and relations as well as part-of-speech tags, among others  To ensure that the automatic classification does not remove suitable propositions, we tuned the classifier to avoid false negatives  In particular, we introduced class weights, improving precision on the negative class at the cost of a higher fraction of positive classifications  Additionally, we manually verified a certain number of the most uncertain negative classifications to further improve performance  When 20% of the classifications are manually verified and corrected, we found that our model trained on 350 labeled instances achieves 93% precision on negative classifications on the unseen 150 instances  We found this to be a reasonable trade-off of automation and data quality and applied the model to the full dataset 
The classifier filtered out 43% of the propositions, leaving 1622 per topic  We manually examined the 17k least confident negative classifications and corrected 955 of them  We also corrected positive classifications for certain types of tuples for which we knew the classifier to be imprecise  Finally, each topic was left with an average of 1554 propositions (47k in total) 
Importance Annotation
Given the propositions identified in the previous step, we now applied our crowdsourcing scheme as described in § SECREF4 to determine their importance  To cope with the large number of propositions, we combine the two task designs: First, we collect Likert-scores from 5 workers for each proposition, clean the data and calculate average scores  Then, using only the top 100 propositions according to these scores, we crowdsource 10% of all possible pairwise comparisons among them  Using TrueSkill, we obtain a fine-grained ranking of the 100 most important propositions 
For Likert-scores, the average agreement over all topics is 0 80, while the majority agreement for comparisons is 0 78  We repeated the data collection for three randomly selected topics and found the Pearson correlation between both runs to be 0 73 (Spearman 0 73) for Likert-scores and 0 72 (Spearman 0 71) for comparisons  These figures show that the crowdsourcing approach works on this dataset as reliably as on the TAC documents 
In total, we uploaded 53k scoring and 12k comparison tasks to Mechanical Turk, spending $4425 45 including fees  From the fine-grained ranking of the 100 most important propositions, we select the top 50 per topic to construct a summary concept map in the subsequent steps 
Proposition Revision
Having a manageable number of propositions, an annotator then applied a few straightforward transformations that correct common errors of the Open IE system  First, we break down propositions with conjunctions in either of the arguments into separate propositions per conjunct, which the Open IE system sometimes fails to do  And second, we correct span errors that might occur in the argument or relation phrases, especially when sentences were not properly segmented  As a result, we have a set of high quality propositions for our concept map, consisting of, due to the first transformation, 56 1 propositions per topic on average 
Concept Map Construction
In this final step, we connect the set of important propositions to form a graph  For instance, given the following two propositions
(student, may borrow, Stafford Loan)
(the student, does not have, a credit history)
one can easily see, although the first arguments differ slightly, that both labels describe the concept student, allowing us to build a concept map with the concepts student, Stafford Loan and credit history  The annotation task thus involves deciding which of the available propositions to include in the map, which of their concepts to merge and, when merging, which of the available labels to use  As these decisions highly depend upon each other and require context, we decided to use expert annotators rather than crowdsource the subtasks 
Annotators were given the topic description and the most important, ranked propositions  Using a simple annotation tool providing a visualization of the graph, they could connect the propositions step by step  They were instructed to reach a size of 25 concepts, the recommended maximum size for a concept map BIBREF6   Further, they should prefer more important propositions and ensure connectedness  When connecting two propositions, they were asked to keep the concept label that was appropriate for both propositions  To support the annotators, the tool used ADW BIBREF40 , a state-of-the-art approach for semantic similarity, to suggest possible connections  The annotation was carried out by graduate students with a background in NLP after receiving an introduction into the guidelines and tool and annotating a first example 
If an annotator was not able to connect 25 concepts, she was allowed to create up to three synthetic relations with freely defined labels, making the maps slightly abstractive  On average, the constructed maps have 0 77 synthetic relations, mostly connecting concepts whose relation is too obvious to be explicitly stated in text (e g  between Montessori teacher and Montessori education) 
To assess the reliability of this annotation step, we had the first three maps created by two annotators  We casted the task of selecting propositions to be included in the map as a binary decision task and observed an agreement of 84% ( INLINEFORM0 )  Second, we modeled the decision which concepts to join as a binary decision on all pairs of common concepts, observing an agreement of 95% ( INLINEFORM1 )  And finally, we compared which concept labels the annotators decided to include in the final map, observing 85% ( INLINEFORM2 ) agreement  Hence, the annotation shows substantial agreement BIBREF41  
Corpus Analysis
In this section, we describe our newly created corpus, which, in addition to having summaries in the form of concept maps, differs from traditional summarization corpora in several aspects 
Document Clusters
The corpus consists of document clusters for 30 different topics  Each of them contains around 40 documents with on average 2413 tokens, which leads to an average cluster size of 97,880 token  With these characteristics, the document clusters are 15 times larger than typical DUC clusters of ten documents and five times larger than the 25-document-clusters (Table TABREF26 )  In addition, the documents are also more variable in terms of length, as the (length-adjusted) standard deviation is twice as high as in the other corpora  With these properties, the corpus represents an interesting challenge towards real-world application scenarios, in which users typically have to deal with much more than ten documents 
Because we used a large web crawl as the source for our corpus, it contains documents from a variety of genres  To further analyze this property, we categorized a sample of 50 documents from the corpus  Among them, we found professionally written articles and blog posts (28%), educational material for parents and kids (26%), personal blog posts (16%), forum discussions and comments (12%), commented link collections (12%) and scientific articles (6%) 
In addition to the variety of genres, the documents also differ in terms of language use  To capture this property, we follow Zopf 2016 and compute, for every topic, the average Jensen-Shannon divergence between the word distribution of one document and the word distribution in the remaining documents  The higher this value is, the more the language differs between documents  We found the average divergence over all topics to be 0 3490, whereas it is 0 3019 in DUC 2004 and 0 3188 in TAC 2008A 
Concept Maps
As Table TABREF33 shows, each of the 30 reference concept maps has exactly 25 concepts and between 24 and 28 relations  Labels for both concepts and relations consist on average of 3 2 tokens, whereas the latter are a bit shorter in characters 
To obtain a better picture of what kind of text spans have been used as labels, we automatically tagged them with their part-of-speech and determined their head with a dependency parser  Concept labels tend to be headed by nouns (82%) or verbs (15%), while they also contain adjectives, prepositions and determiners  Relation labels, on the other hand, are almost always headed by a verb (94%) and contain prepositions, nouns and particles in addition  These distributions are very similar to those reported by Villalon 2010 for their (single-document) concept map corpus 
Analyzing the graph structure of the maps, we found that all of them are connected  They have on average 7 2 central concepts with more than one relation, while the remaining ones occur in only one proposition  We found that achieving a higher number of connections would mean compromising importance, i e  including less important propositions, and decided against it 
Baseline Experiments
In this section, we briefly describe a baseline and evaluation scripts that we release, with a detailed documentation, along with the corpus 
Conclusion
In this work, we presented low-context importance annotation, a novel crowdsourcing scheme that we used to create a new benchmark corpus for concept-map-based MDS  The corpus has large-scale document clusters of heterogeneous web documents, posing a challenging summarization task  Together with the corpus, we provide implementations of a baseline method and evaluation scripts and hope that our efforts facilitate future research on this variant of summarization 
Acknowledgments
We would like to thank Teresa Botschen, Andreas Hanselowski and Markus Zopf for their help with the annotation work and Christian Meyer for his valuable feedback  This work has been supported by the German Research Foundation as part of the Research Training Group “Adaptive Preparation of Information from Heterogeneous Sources” (AIPHES) under grant No  GRK 1994/1 
Context 2: Introduction
Sarcasm is defined as “a sharp, bitter, or cutting expression or remark; a bitter gibe or taunt”  As the fields of affective computing and sentiment analysis have gained increasing popularity BIBREF0 , it is a major concern to detect sarcastic, ironic, and metaphoric expressions  Sarcasm, especially, is key for sentiment analysis as it can completely flip the polarity of opinions  Understanding the ground truth, or the facts about a given event, allows for the detection of contradiction between the objective polarity of the event (usually negative) and its sarcastic characteristic by the author (usually positive), as in “I love the pain of breakup”  Obtaining such knowledge is, however, very difficult 
In our experiments, we exposed the classifier to such knowledge extracted indirectly from Twitter  Namely, we used Twitter data crawled in a time period, which likely contain both the sarcastic and non-sarcastic accounts of an event or similar events  We believe that unambiguous non-sarcastic sentences provided the classifier with the ground-truth polarity of those events, which the classifier could then contrast with the opposite estimations in sarcastic sentences  Twitter is a more suitable resource for this purpose than blog posts, because the polarity of short tweets is easier to detect (as all the information necessary to detect polarity is likely to be contained in the same sentence) and because the Twitter API makes it easy to collect a large corpus of tweets containing both sarcastic and non-sarcastic examples of the same event 
Sometimes, however, just knowing the ground truth or simple facts on the topic is not enough, as the text may refer to other events in order to express sarcasm  For example, the sentence “If Hillary wins, she will surely be pleased to recall Monica each time she enters the Oval Office :P :D”, which refers to the 2016 US presidential election campaign and to the events of early 1990's related to the US president Clinton, is sarcastic because Hillary, a candidate and Clinton's wife, would in fact not be pleased to recall her husband's alleged past affair with Monica Lewinsky  The system, however, would need a considerable amount of facts, commonsense knowledge, anaphora resolution, and logical reasoning to draw such a conclusion  In this paper, we will not deal with such complex cases 
Existing works on sarcasm detection have mainly focused on unigrams and the use of emoticons BIBREF1 , BIBREF2 , BIBREF3 , unsupervised pattern mining approach BIBREF4 , semi-supervised approach BIBREF5 and n-grams based approach BIBREF6 , BIBREF7 , BIBREF8 , BIBREF9 with sentiment features  Instead, we propose a framework that learns sarcasm features automatically from a sarcasm corpus using a convolutional neural network (CNN)  We also investigate whether features extracted using the pre-trained sentiment, emotion and personality models can improve sarcasm detection performance  Our approach uses relatively lower dimensional feature vectors and outperforms the state of the art on different datasets  In summary, the main contributions of this paper are the following:
The rest of the paper is organized as follows: Section SECREF2 proposes a brief literature review on sarcasm detection; Section SECREF4 presents the proposed approach; experimental results and thorough discussion on the experiments are given in Section SECREF5 ; finally, Section SECREF6 concludes the paper 
Related Works
NLP research is gradually evolving from lexical to compositional semantics BIBREF10 through the adoption of novel meaning-preserving and context-aware paradigms such as convolutional networks BIBREF11 , recurrent belief networks BIBREF12 , statistical learning theory BIBREF13 , convolutional multiple kernel learning BIBREF14 , and commonsense reasoning BIBREF15   But while other NLP tasks have been extensively investigated, sarcasm detection is a relatively new research topic which has gained increasing interest only recently, partly thanks to the rise of social media analytics and sentiment analysis  Sentiment analysis BIBREF16 and using multimodal information as a new trend BIBREF17 , BIBREF18 , BIBREF19 , BIBREF20 , BIBREF14 is a popular branch of NLP research that aims to understand sentiment of documents automatically using combination of various machine learning approaches BIBREF21 , BIBREF22 , BIBREF20 , BIBREF23  
An early work in this field was done by BIBREF6 on a dataset of 6,600 manually annotated Amazon reviews using a kNN-classifier over punctuation-based and pattern-based features, i e , ordered sequence of high frequency words  BIBREF1 used support vector machine (SVM) and logistic regression over a feature set of unigrams, dictionary-based lexical features and pragmatic features (e g , emoticons) and compared the performance of the classifier with that of humans  BIBREF24 described a set of textual features for recognizing irony at a linguistic level, especially in short texts created via Twitter, and constructed a new model that was assessed along two dimensions: representativeness and relevance  BIBREF5 used the presence of a positive sentiment in close proximity of a negative situation phrase as a feature for sarcasm detection  BIBREF25 used the Balanced Window algorithm for classifying Dutch tweets as sarcastic vs  non-sarcastic; n-grams (uni, bi and tri) and intensifiers were used as features for classification 
BIBREF26 compared the performance of different classifiers on the Amazon review dataset using the imbalance between the sentiment expressed by the review and the user-given star rating  Features based on frequency (gap between rare and common words), written spoken gap (in terms of difference between usage), synonyms (based on the difference in frequency of synonyms) and ambiguity (number of words with many synonyms) were used by BIBREF3 for sarcasm detection in tweets  BIBREF9 proposed the use of implicit incongruity and explicit incongruity based features along with lexical and pragmatic features, such as emoticons and punctuation marks  Their method is very much similar to the method proposed by BIBREF5 except BIBREF9 used explicit incongruity features  Their method outperforms the approach by BIBREF5 on two datasets 
BIBREF8 compared the performance with different language-independent features and pre-processing techniques for classifying text as sarcastic and non-sarcastic  The comparison was done over three Twitter dataset in two different languages, two of these in English with a balanced and an imbalanced distribution and the third one in Czech  The feature set included n-grams, word-shape patterns, pointedness and punctuation-based features 
In this work, we use features extracted from a deep CNN for sarcasm detection  Some of the key differences between the proposed approach and existing methods include the use of a relatively smaller feature set, automatic feature extraction, the use of deep networks, and the adoption of pre-trained NLP models 
Sentiment Analysis and Sarcasm Detection
Sarcasm detection is an important subtask of sentiment analysis BIBREF27   Since sarcastic sentences are subjective, they carry sentiment and emotion-bearing information  Most of the studies in the literature BIBREF28 , BIBREF29 , BIBREF9 , BIBREF30 include sentiment features in sarcasm detection with the use of a state-of-the-art sentiment lexicon  Below, we explain how sentiment information is key to express sarcastic opinions and the approach we undertake to exploit such information for sarcasm detection 
In general, most sarcastic sentences contradict the fact  In the sentence “I love the pain present in the breakups" (Figure FIGREF4 ), for example, the word “love" contradicts “pain present in the breakups”, because in general no-one loves to be in pain  In this case, the fact (i e , “pain in the breakups") and the contradictory statement to that fact (i e , “I love") express sentiment explicitly  Sentiment shifts from positive to negative but, according to sentic patterns BIBREF31 , the literal sentiment remains positive  Sentic patterns, in fact, aim to detect the polarity expressed by the speaker; thus, whenever the construction “I love” is encountered, the sentence is positive no matter what comes after it (e g , “I love the movie that you hate”)  In this case, however, the sentence carries sarcasm and, hence, reflects the negative sentiment of the speaker 
In another example (Figure FIGREF4 ), the fact, i e , “I left the theater during the interval", has implicit negative sentiment  The statement “I love the movie" contradicts the fact “I left the theater during the interval"; thus, the sentence is sarcastic  Also in this case the sentiment shifts from positive to negative and hints at the sarcastic nature of the opinion 
The above discussion has made clear that sentiment (and, in particular, sentiment shifts) can largely help to detect sarcasm  In order to include sentiment shifting into the proposed framework, we train a sentiment model for sentiment-specific feature extraction  Training with a CNN helps to combine the local features in the lower layers into global features in the higher layers  We do not make use of sentic patterns BIBREF31 in this paper but we do plan to explore that research direction as a part of our future work  In the literature, it is found that sarcasm is user-specific too, i e , some users have a particular tendency to post more sarcastic tweets than others  This acts as a primary intuition for us to extract personality-based features for sarcasm detection 
The Proposed Framework
As discussed in the literature BIBREF5 , sarcasm detection may depend on sentiment and other cognitive aspects  For this reason, we incorporate both sentiment and emotion clues in our framework  Along with these, we also argue that personality of the opinion holder is an important factor for sarcasm detection  In order to address all of these variables, we create different models for each of them, namely: sentiment, emotion and personality  The idea is to train each model on its corresponding benchmark dataset and, hence, use such pre-trained models together to extract sarcasm-related features from the sarcasm datasets 
Now, the viable research question here is - Do these models help to improve sarcasm detection performance?' Literature shows that they improve the performance but not significantly  Thus, do we need to consider those factors in spotting sarcastic sentences? Aren't n-grams enough for sarcasm detection? Throughout the rest of this paper, we address these questions in detail  The training of each model is done using a CNN  Below, we explain the framework in detail  Then, we discuss the pre-trained models  Figure FIGREF6 presents a visualization of the proposed framework 
General CNN Framework
CNN can automatically extract key features from the training data  It grasps contextual local features from a sentence and, after several convolution operations, it forms a global feature vector out of those local features  CNN does not need the hand-crafted features used in traditional supervised classifiers  Such hand-crafted features are difficult to compute and a good guess for encoding the features is always necessary in order to get satisfactory results  CNN, instead, uses a hierarchy of local features which are important to learn context  The hand-crafted features often ignore such a hierarchy of local features 
Features extracted by CNN can therefore be used instead of hand-crafted features, as they carry more useful information  The idea behind convolution is to take the dot product of a vector of INLINEFORM0 weights INLINEFORM1 also known as kernel vector with each INLINEFORM2 -gram in the sentence INLINEFORM3 to obtain another sequence of features INLINEFORM4   DISPLAYFORM0
Thus, a max pooling operation is applied over the feature map and the maximum value INLINEFORM0 is taken as the feature corresponding to this particular kernel vector  Similarly, varying kernel vectors and window sizes are used to obtain multiple features BIBREF32   For each word INLINEFORM1 in the vocabulary, a INLINEFORM2 -dimensional vector representation is given in a look up table that is learned from the data BIBREF33   The vector representation of a sentence, hence, is a concatenation of vectors for individual words  Similarly, we can have look up tables for other features  One might want to provide features other than words if these features are suspected to be helpful  The convolution kernels are then applied to word vectors instead of individual words 
We use these features to train higher layers of the CNN, in order to represent bigger groups of words in sentences  We denote the feature learned at hidden neuron INLINEFORM0 in layer INLINEFORM1 as INLINEFORM2   Multiple features may be learned in parallel in the same CNN layer  The features learned in each layer are used to train the next layer: DISPLAYFORM0
where * indicates convolution and INLINEFORM0 is a weight kernel for hidden neuron INLINEFORM1 and INLINEFORM2 is the total number of hidden neurons  The CNN sentence model preserves the order of words by adopting convolution kernels of gradually increasing sizes that span an increasing number of words and ultimately the entire sentence  As mentioned above, each word in a sentence is represented using word embeddings 
We employ the publicly available word2vec vectors, which were trained on 100 billion words from Google News  The vectors are of dimensionality 300, trained using the continuous bag-of-words architecture BIBREF33   Words not present in the set of pre-trained words are initialized randomly  However, while training the neural network, we use non-static representations  These include the word vectors, taken as input, into the list of parameters to be learned during training 
Two primary reasons motivated us to use non-static channels as opposed to static ones  Firstly, the common presence of informal language and words in tweets resulted in a relatively high random initialization of word vectors due to the unavailability of these words in the word2vec dictionary  Secondly, sarcastic sentences are known to include polarity shifts in sentimental and emotional degrees  For example, “I love the pain present in breakups" is a sarcastic sentence with a significant change in sentimental polarity  As word2vec was not trained to incorporate these nuances, we allow our models to update the embeddings during training in order to include them  Each sentence is wrapped to a window of INLINEFORM0 , where INLINEFORM1 is the maximum number of words amongst all sentences in the dataset  We use the output of the fully-connected layer of the network as our feature vector 
We have done two kinds of experiments: firstly, we used CNN for the classification; secondly, we extracted features from the fully-connected layer of the CNN and fed them to an SVM for the final classification  The latter CNN-SVM scheme is quite useful for text classification as shown by Poria et al  BIBREF18   We carry out n-fold cross-validation on the dataset using CNN  In every fold iteration, in order to obtain the training and test features, the output of the fully-connected layer is treated as features to be used for the final classification using SVM  Table TABREF12 shows the training settings for each CNN model developed in this work  ReLU is used as the non-linear activation function of the network  The network configurations of all models developed in this work are given in Table TABREF12  
Sentiment Feature Extraction Model
As discussed above, sentiment clues play an important role for sarcastic sentence detection  In our work, we train a CNN (see Section SECREF5 for details) on a sentiment benchmark dataset  This pre-trained model is then used to extract features from the sarcastic datasets  In particular, we use Semeval 2014 BIBREF34 Twitter Sentiment Analysis Dataset for the training  This dataset contains 9,497 tweets out of which 5,895 are positive, 3,131 are negative and 471 are neutral  The fully-connected layer of the CNN used for sentiment feature extraction has 100 neurons, so 100 features are extracted from this pre-trained model  The final softmax determines whether a sentence is positive, negative or neutral  Thus, we have three neurons in the softmax layer 
Emotion Feature Extraction Model
We use the CNN structure as described in Section SECREF5 for emotional feature extraction  As a dataset for extracting emotion-related features, we use the corpus developed by BIBREF35   This dataset consists of blog posts labeled by their corresponding emotion categories  As emotion taxonomy, the authors used six basic emotions, i e , Anger, Disgust, Surprise, Sadness, Joy and Fear  In particular, the blog posts were split into sentences and each sentence was labeled  The dataset contains 5,205 sentences labeled by one of the emotion labels  After employing this model on the sarcasm dataset, we obtained a 150-dimensional feature vector from the fully-connected layer  As the aim of training is to classify each sentence into one of the six emotion classes, we used six neurons in the softmax layer 
Personality Feature Extraction Model
Detecting personality from text is a well-known challenging problem  In our work, we use five personality traits described by BIBREF36 , i e , Openness, Conscientiousness, Extraversion, Agreeableness, and Neuroticism, sometimes abbreviated as OCEAN (by their first letters)
Context 3: Introduction
Data imbalance is a common issue in a variety of NLP tasks such as tagging and machine reading comprehension  Table TABREF3 gives concrete examples: for the Named Entity Recognition (NER) task BIBREF2, BIBREF3, most tokens are backgrounds with tagging class $O$  Specifically, the number of tokens tagging class $O$ is 5 times as many as those with entity labels for the CoNLL03 dataset and 8 times for the OntoNotes5 0 dataset; Data-imbalanced issue is more severe for MRC tasks BIBREF4, BIBREF5, BIBREF6, BIBREF7, BIBREF8 with the value of negative-positive ratio being 50-200 
Data imbalance results in the following two issues: (1) the training-test discrepancy: Without balancing the labels, the learning process tends to converge to a point that strongly biases towards class with the majority label  This actually creates a discrepancy between training and test: at training time, each training instance contributes equally to the objective function while at test time, F1 score concerns more about positive examples; (2) the overwhelming effect of easy-negative examples  As pointed out by meng2019dsreg, significantly large number of negative examples also means that the number of easy-negative example is large  The huge number of easy examples tends to overwhelm the training, making the model not sufficiently learned to distinguish between positive examples and hard-negative examples  The cross-entropy objective (CE for short) or maximum likelihood (MLE) objective, which is widely adopted as the training objective for data-imbalanced NLP tasks BIBREF9, BIBREF10, BIBREF11, BIBREF12, BIBREF13, BIBREF14, BIBREF15, handles neither of the issues 
To handle the first issue, we propose to replace CE or MLE with losses based on the Sørensen–Dice coefficient BIBREF0 or Tversky index BIBREF1  The Sørensen–Dice coefficient, dice loss for short, is the harmonic mean of precision and recall  It attaches equal importance to false positives (FPs) and false negatives (FNs) and is thus more immune to data-imbalanced datasets  Tversky index extends dice loss by using a weight that trades precision and recall, which can be thought as the approximation of the $F_{\beta }$ score, and thus comes with more flexibility  Therefore, We use dice loss or Tversky index to replace CE loss to address the first issue 
Only using dice loss or Tversky index is not enough since they are unable to address the dominating influence of easy-negative examples  This is intrinsically because dice loss is actually a hard version of the F1 score  Taking the binary classification task as an example, at test time, an example will be classified as negative as long as its probability is smaller than 0 5, but training will push the value to 0 as much as possible  This gap isn't a big issue for balanced datasets, but is extremely detrimental if a big proportion of training examples are easy-negative ones: easy-negative examples can easily dominate training since their probabilities can be pushed to 0 fairly easily  Meanwhile, the model can hardly distinguish between hard-negative examples and positive ones  Inspired by the idea of focal loss BIBREF16 in computer vision, we propose a dynamic weight adjusting strategy, which associates each training example with a weight in proportion to $(1-p)$, and this weight dynamically changes as training proceeds  This strategy helps to deemphasize confident examples during training as their $p$ approaches the value of 1, makes the model attentive to hard-negative examples, and thus alleviates the dominating effect of easy-negative examples 
Combing both strategies, we observe significant performance boosts on a wide range of data imbalanced NLP tasks  Notably, we are able to achieve SOTA results on CTB5 (97 92, +1 86), CTB6 (96 57, +1 80) and UD1 4 (96 98, +2 19) for the POS task; SOTA results on CoNLL03 (93 33, +0 29), OntoNotes5 0 (92 07, +0 96)), MSRA 96 72(+0 97) and OntoNotes4 0 (84 47,+2 36) for the NER task; along with competitive results on the tasks of machine reading comprehension and paraphrase identification 
The rest of this paper is organized as follows: related work is presented in Section 2  We describe different training objectives in Section 3  Experimental results are presented in Section 4  We perform ablation studies in Section 5, followed by a brief conclusion in Section 6 
Related Work ::: Data Resample
The idea of weighting training examples has a long history  Importance sampling BIBREF17 assigns weights to different samples and changes the data distribution  Boosting algorithms such as AdaBoost BIBREF18 select harder examples to train subsequent classifiers  Similarly, hard example mining BIBREF19 downsamples the majority class and exploits the most difficult examples  Oversampling BIBREF20, BIBREF21 is used to balance the data distribution  Another line of data resampling is to dynamically control the weights of examples as training proceeds  For example, focal loss BIBREF16 used a soft weighting scheme that emphasizes harder examples during training  In self-paced learning BIBREF22, example weights are obtained through optimizing the weighted training loss which encourages learning easier examples first  At each training step, self-paced learning algorithm optimizes model parameters and example weights jointly  Other works BIBREF23, BIBREF24 adjusted the weights of different training examples based on training loss  Besides, recent work BIBREF25, BIBREF26 proposed to learn a separate network to predict sample weights 
Related Work ::: Data Imbalance Issue in Object Detection
The background-object label imbalance issue is severe and thus well studied in the field of object detection BIBREF27, BIBREF28, BIBREF29, BIBREF30, BIBREF31  The idea of hard negative mining (HNM) BIBREF30 has gained much attention recently  shrivastava2016ohem proposed the online hard example mining (OHEM) algorithm in an iterative manner that makes training progressively more difficult, and pushes the model to learn better  ssd2016liu sorted all of the negative samples based on the confidence loss and picking the training examples with the negative-positive ratio at 3:1  pang2019rcnn proposed a novel method called IoU-balanced sampling and aploss2019chen designed a ranking model to replace the conventional classification task with a average-precision loss to alleviate the class imbalance issue  The efforts made on object detection have greatly inspired us to solve the data imbalance issue in NLP 
Losses ::: Notation
For illustration purposes, we use the binary classification task to demonstrate how different losses work  The mechanism can be easily extended to multi-class classification 
Let $\lbrace x_i\rbrace $ denote a set of instances  Each $x_i$ is associated with a golden label vector $y_i = [y_{i0},y_{i1} ]$, where $y_{i1}\in \lbrace 0,1\rbrace $ and $y_{i0}\in \lbrace 0,1\rbrace $ respectively denote the positive and negative classes, and thus $y_i$ can be either $[0,1]$ or $[0,1]$  Let $p_i = [p_{i0},p_{i1} ]$ denote the probability vector, and $p_{i1}$ and $p_{i0}$ respectively denote the probability that a model assigns the positive and negative label to $x_i$ 
Losses ::: Cross Entropy Loss
The vanilla cross entropy (CE) loss is given by:
As can be seen from Eq DISPLAY_FORM8, each $x_i$ contributes equally to the final objective  Two strategies are normally used to address the the case where we wish that not all $x_i$ are treated equal: associating different classes with different weighting factor $\alpha $ or resampling the datasets  For the former, Eq DISPLAY_FORM8 is adjusted as follows:
where $\alpha _i\in [0,1]$ may be set by the inverse class frequency or treated as a hyperparameter to set by cross validation  In this work, we use $\lg (\frac{n-n_t}{n_t}+K)$ to calculate the coefficient $\alpha $, where $n_t$ is the number of samples with class $t$ and $n$ is the total number of samples in the training set  $K$ is a hyperparameter to tune  The data resampling strategy constructs a new dataset by sampling training examples from the original dataset based on human-designed criteria, e g , extract equal training samples from each class  Both strategies are equivalent to changing the data distribution and thus are of the same nature  Empirically, these two methods are not widely used due to the trickiness of selecting $\alpha $ especially for multi-class classification tasks and that inappropriate selection can easily bias towards rare classes BIBREF32 
Losses ::: Dice coefficient and Tversky index
Sørensen–Dice coefficient BIBREF0, BIBREF33, dice coefficient (DSC) for short, is a F1-oriented statistic used to gauge the similarity of two sets  Given two sets $A$ and $B$, the dice coefficient between them is given as follows:
In our case, $A$ is the set that contains of all positive examples predicted by a specific model, and $B$ is the set of all golden positive examples in the dataset  When applied to boolean data with the definition of true positive (TP), false positive (FP), and false negative (FN), it can be then written as follows:
For an individual example $x_i$, its corresponding DSC loss is given as follows:
As can be seen, for a negative example with $y_{i1}=0$, it does not contribute to the objective  For smoothing purposes, it is common to add a $\gamma $ factor to both the nominator and the denominator, making the form to be as follows:
As can be seen, negative examples, with $y_{i1}$ being 0 and DSC being $\frac{\gamma }{ p_{i1}+\gamma }$, also contribute to the training  Additionally, milletari2016v proposed to change the denominator to the square form for faster convergence, which leads to the following dice loss (DL):
Another version of DL is to directly compute set-level dice coefficient instead of the sum of individual dice coefficient  We choose the latter due to ease of optimization

ground_truth: Answer with content missing: (Evaluation Metrics section) Precision, Recall, F1-scores, Strict match, METEOR, ROUGE-2

prompt_front: You are given a scientific article and a question. Answer the question as concisely as you can, using a single phrase or sentence if possible. If the question cannot be answered based on the information in the article, write "unanswerable". If the question is a yes/no question, answer "yes", "no", or "unanswerable". Do not provide any explanation.

Please answer the questions based on the text provided below. What are the network's baseline features?
Context 2:  As a training dataset, we use the corpus developed by BIBREF36 , which contains 2,400 essays labeled by one of the five personality traits each 
The fully-connected layer has 150 neurons, which are treated as the features  We concatenate the feature vector of each personality dimension in order to create the final feature vector  Thus, the personality model ultimately extracts a 750-dimensional feature vector (150-dimensional feature vector for each of the five personality traits)  This network is replicated five times, one for each personality trait  In particular, we create a CNN for each personality trait and the aim of each CNN is to classify a sentence into binary classes, i e , whether it expresses a personality trait or not 
Baseline Method and Features
CNN can also be employed on the sarcasm datasets in order to identify sarcastic and non-sarcastic tweets  We term the features extracted from this network baseline features, the method as baseline method and the CNN architecture used in this baseline method as baseline CNN  Since the fully-connected layer has 100 neurons, we have 100 baseline features in our experiment  This method is termed baseline method as it directly aims to classify a sentence as sarcastic vs non-sarcastic  The baseline CNN extracts the inherent semantics from the sarcastic corpus by employing deep domain understanding  The process of using baseline features with other features extracted from the pre-trained model is described in Section SECREF24  
Experimental Results and Discussion
In this section, we present the experimental results using different feature combinations and compare them with the state of the art  For each feature we show the results using only CNN and using CNN-SVM (i e , when the features extracted by CNN are fed to the SVM)  Macro-F1 measure is used as an evaluation scheme in the experiments 
Sarcasm Datasets Used in the Experiment
This dataset was created by BIBREF8   The tweets were downloaded from Twitter using #sarcasm as a marker for sarcastic tweets  It is a monolingual English dataset which consists of a balanced distribution of 50,000 sarcastic tweets and 50,000 non-sarcastic tweets 
Since sarcastic tweets are less frequently used BIBREF8 , we also need to investigate the robustness of the selected features and the model trained on these features on an imbalanced dataset  To this end, we used another English dataset from BIBREF8   It consists of 25,000 sarcastic tweets and 75,000 non-sarcastic tweets 
We have obtained this dataset from The Sarcasm Detector  It contains 120,000 tweets, out of which 20,000 are sarcastic and 100,000 are non-sarcastic  We randomly sampled 10,000 sarcastic and 20,000 non-sarcastic tweets from the dataset  Visualization of both the original and subset data show similar characteristics 
A two-step methodology has been employed in filtering the datasets used in our experiments  Firstly, we identified and removed all the “user", “URL" and “hashtag" references present in the tweets using efficient regular expressions  Special emphasis was given to this step to avoid traces of hashtags, which might trigger the models to provide biased results  Secondly, we used NLTK Twitter Tokenizer to ensure proper tokenization of words along with special symbols and emoticons  Since our deep CNNs extract contextual information present in tweets, we include emoticons as part of the vocabulary  This enables the emoticons to hold a place in the word embedding space and aid in providing information about the emotions present in the sentence 
Merging the Features
Throughout this research, we have carried out several experiments with various feature combinations  For the sake of clarity, we explain below how the features extracted using difference models are merged 
In the standard feature merging process, we first extract the features from all deep CNN based feature extraction models and then we concatenate them  Afterwards, SVM is employed on the resulted feature vector 
In another setting, we use the features extracted from the pre-trained models as the static channels of features in the CNN of the baseline method  These features are appended to the hidden layer of the baseline CNN, preceding the final output softmax layer 
For comparison, we have re-implemented the state-of-the-art methods  Since BIBREF9 did not mention about the sentiment lexicon they use in the experiment, we used SenticNet BIBREF37 in the re-implementation of their method 
Results on Dataset 1
As shown in Table TABREF29 , for every feature CNN-SVM outperforms the performance of the CNN  Following BIBREF6 , we have carried out a 5-fold cross-validation on this dataset  The baseline features ( SECREF16 ) perform best among other features  Among all the pre-trained models, the sentiment model (F1-score: 87 00%) achieves better performance in comparison with the other two pre-trained models  Interestingly, when we merge the baseline features with the features extracted by the pre-trained deep NLP models, we only get 0 11% improvement over the F-score  It means that the baseline features alone are quite capable to detect sarcasm  On the other hand, when we combine sentiment, emotion and personality features, we obtain 90 70% F1-score  This indicates that the pre-trained features are indeed useful for sarcasm detection  We also compare our approach with the best research study conducted on this dataset (Table TABREF30 )  Both the proposed baseline model and the baseline + sentiment + emotion + personality model outperform the state of the art BIBREF9 , BIBREF8   One important difference with the state of the art is that BIBREF8 used relatively larger feature vector size ( INLINEFORM0 500,000) than we used in our experiment (1,100)  This not only prevents our model to overfit the data but also speeds up the computation  Thus, we obtain an improvement in the overall performance with automatic feature extraction using a relatively lower dimensional feature space 
In the literature, word n-grams, skipgrams and character n-grams are used as baseline features  According to Ptacek et al  BIBREF8 , these baseline features along with the other features (sentiment features and part-of-speech based features) produced the best performance  However, Ptacek et al  did not analyze the performance of these features when they were not used with the baseline features  Pre-trained word embeddings play an important role in the performance of the classifier because, when we use randomly generated embeddings, performance falls down to 86 23% using all features 
Results on Dataset 2
5-fold cross-validation has been carried out on Dataset 2  Also for this dataset, we get the best accuracy when we use all features  Baseline features have performed significantly better (F1-score: 92 32%) than all other features  Supporting the observations we have made from the experiments on Dataset 1, we see CNN-SVM outperforming CNN on Dataset 2  However, when we use all the features, CNN alone (F1-score: 89 73%) does not outperform the state of the art BIBREF8 (F1-score: 92 37%)  As shown in Table TABREF30 , CNN-SVM on the baseline + sentiment + emotion + personality feature set outperforms the state of the art (F1-score: 94 80%)  Among the pre-trained models, the sentiment model performs best (F1-score: 87 00%) 
Table TABREF29 shows the performance of different feature combinations  The gap between the F1-scores of only baseline features and all features is larger on the imbalanced dataset than the balanced dataset  This supports our claim that sentiment, emotion and personality features are very useful for sarcasm detection, thanks to the pre-trained models  The F1-score using sentiment features when combined with baseline features is 94 60%  On both of the datasets, emotion and sentiment features perform better than the personality features  Interestingly, using only sentiment, emotion and personality features, we achieve 90 90% F1-score 
Results on Dataset 3
Experimental results on Dataset 3 show the similar trends (Table TABREF30 ) as compared to Dataset 1 and Dataset 2  The highest performance (F1-score 93 30%) is obtained when we combine baseline features with sentiment, emotion and personality features  In this case, also CNN-SVM consistently performs better than CNN for every feature combination  The sentiment model is found to be the best pre-trained model  F1-score of 84 43% is obtained when we merge sentiment, emotion and personality features 
Dataset 3 is more complex and non-linear in nature compared to the other two datasets  As shown in Table TABREF30 , the methods by BIBREF9 and BIBREF8 perform poorly on this dataset  The TP rate achieved by BIBREF9 is only 10 07% and that means their method suffers badly on complex data  The approach of BIBREF8 has also failed to perform well on Dataset 3, achieving 62 37% with a better TP rate of 22 15% than BIBREF9   On the other hand, our proposed model performs consistently well on this dataset achieving 93 30% 
Testing Generalizability of the Models and Discussions
To test the generalization capability of the proposed approach, we perform training on Dataset 1 and test on Dataset 3  The F1-score drops down dramatically to 33 05%  In order to understand this finding, we visualize each dataset using PCA (Figure FIGREF17 )  It depicts that, although Dataset 1 is mostly linearly separable, Dataset 3 is not  A linear kernel that performs well on Dataset 1 fails to provide good performance on Dataset 3  If we use RBF kernel, it overfits the data and produces worse results than what we get using linear kernel  Similar trends are seen in the performance of other two state-of-the-art approaches BIBREF9 , BIBREF8   Thus, we decide to perform training on Dataset 3 and test on the Dataset 1  As expected better performance is obtained with F1-score 76 78%  However, the other two state-of-the-art approaches fail to perform well in this setting  While the method by BIBREF9 obtains F1-score of 47 32%, the approach by BIBREF8 achieves 53 02% F1-score when trained on Dataset 3 and tested on Dataset 1  Below, we discuss about this generalizability issue of the models developed or referred in this paper 
As discussed in the introduction, sarcasm is very much topic-dependent and highly contextual  For example, let us consider the tweet “I am so glad to see Tanzania played very well, I can now sleep well :P"  Unless one knows that Tanzania actually did not play well in that game, it is not possible to spot the sarcastic nature of this sentence  Thus, an n-gram based sarcasm detector trained at time INLINEFORM0 may perform poorly to detect sarcasm in the tweets crawled at time INLINEFORM1 (given that there is a considerable gap between these time stamps) because of the diversity of the topics (new events occur, new topics are discussed) of the tweets  Sentiment and other contextual clues can help to spot the sarcastic nature in this kind of tweets  A highly positive statement which ends with a emoticon expressing joke can be sarcastic 
State-of-the-art methods lack these contextual information which, in our case, we extract using pre-trained sentiment, emotion and personality models  Not only these pre-trained models, the baseline method (baseline CNN architecture) performs better than the state-of-the-art models in this generalizability test setting  In our generalizability test, when the pre-trained features are used with baseline features, we get 4 19% F1-score improvement over the baseline features  On the other hand, when they are not used with the baseline features, together they produce 64 25% F1-score 
Another important fact is that an n-grams model cannot perform well on unseen data unless it is trained on a very large corpus  If most of the n-grams extracted from the unseen data are not in the vocabulary of the already trained n-grams model, in fact, the model will produce a very sparse feature vector representation of the dataset  Instead, we use the word2vec embeddings as the source of the features, as word2vec allows for the computation of similarities between unseen data and training data 
Baseline Features vs Pre-trained Features
Our experimental results show that the baseline features outperform the pre-trained features for sarcasm detection  However, the combination of pre-trained features and baseline features beats both of themselves alone  It is counterintuitive, since experimental results prove that both of those features learn almost the same global and contextual features  In particular, baseline network dominates over pre-trained network as the former learns most of the features learned by the latter  Nonetheless, the combination of baseline and pre-trained classifiers improves the overall performance and generalizability, hence proving their effectiveness in sarcasm detection  Experimental results show that sentiment and emotion features are the most useful features, besides baseline features (Figure FIGREF36 )  Therefore, in order to reach a better understanding of the relation between personality features among themselves and with other pre-trained features, we carried out Spearman correlation testing  Results, displayed in Table TABREF39 , show that those features are highly correlated with each other 
Conclusion
In this work, we developed pre-trained sentiment, emotion and personality models for identifying sarcastic text using CNN, which are found to be very effective for sarcasm detection  In the future, we plan to evaluate the performance of the proposed method on a large corpus and other domain-dependent corpora  Future work will also focus on analyzing past tweets and activities of users in order to better understand their personality and profile and, hence, further improve the disambiguation between sarcastic and non-sarcastic text 
Context 3: 
Tversky index (TI), which can be thought as the approximation of the $F_{\beta }$ score, extends dice coefficient to a more general case  Given two sets $A$ and $B$, tversky index is computed as follows:
Tversky index offers the flexibility in controlling the tradeoff between false-negatives and false-positives  It degenerates to DSC if $\alpha =\beta =0 5$  The Tversky loss (TL) for the training set $\lbrace x_i,y_i\rbrace $ is thus as follows:
Losses ::: Self-adusting Dice Loss
Consider a simple case where the dataset consists of only one example $x_i$, which is classified as positive as long as $p_{i1}$ is larger than 0 5  The computation of $F1$ score is actually as follows:
Comparing Eq DISPLAY_FORM14 with Eq DISPLAY_FORM22, we can see that Eq DISPLAY_FORM14 is actually a soft form of $F1$, using a continuous $p$ rather than the binary $\mathbb {I}( p_{i1}>0 5)$  This gap isn't a big issue for balanced datasets, but is extremely detrimental if a big proportion of training examples are easy-negative ones: easy-negative examples can easily dominate training since their probabilities can be pushed to 0 fairly easily  Meanwhile, the model can hardly distinguish between hard-negative examples and positive ones, which has a huge negative effect on the final F1 performance 
To address this issue, we propose to multiply the soft probability $p$ with a decaying factor $(1-p)$, changing Eq DISPLAY_FORM22 to the following form:
One can think $(1-p_{i1})$ as a weight associated with each example, which changes as training proceeds  The intuition of changing $p_{i1}$ to $(1-p_{i1}) p_{i1}$ is to push down the weight of easy examples  For easy examples whose probability are approaching 0 or 1, $(1-p_{i1}) p_{i1}$ makes the model attach significantly less focus to them  Figure FIGREF23 gives gives an explanation from the perspective in derivative: the derivative of $\frac{(1-p)p}{1+(1-p)p}$ with respect to $p$ approaches 0 immediately after $p$ approaches 0, which means the model attends less to examples once they are correctly classified 
A close look at Eq DISPLAY_FORM14 reveals that it actually mimics the idea of focal loss (FL for short) BIBREF16 for object detection in vision  Focal loss was proposed for one-stage object detector to handle foreground-background tradeoff encountered during training  It down-weights the loss assigned to well-classified examples by adding a $(1-p)^{\beta }$ factor, leading the final loss to be $(1-p)^{\beta }\log p$ 
In Table TABREF18, we show the losses used in our experiments, which is described in the next section 
Experiments
We evaluate the proposed method on four NLP tasks: part-of-speech tagging, named entity recognition, machine reading comprehension and paraphrase identification  Baselines in our experiments are optimized by using the standard cross-entropy training objective 
Experiments ::: Part-of-Speech Tagging
Part-of-speech tagging (POS) is the task of assigning a label (e g , noun, verb, adjective) to each word in a given text  In this paper, we choose BERT as the backbone and conduct experiments on three Chinese POS datasets  We report the span-level micro-averaged precision, recall and F1 for evaluation  Hyperparameters are tuned on the corresponding development set of each dataset 
Experiments ::: Part-of-Speech Tagging ::: Datasets
We conduct experiments on the widely used Chinese Treebank 5 0, 6 0 as well as UD1 4 
CTB5 is a Chinese dataset for tagging and parsing, which contains 507,222 words, 824,983 characters and 18,782 sentences extracted from newswire sources 
CTB6 is an extension of CTB5, containing 781,351 words, 1,285,149 characters and 28,295 sentences 
UD is the abbreviation of Universal Dependencies, which is a framework for consistent annotation of grammar (parts of speech, morphological features, and syntactic dependencies) across different human languages  In this work, we use UD1 4 for Chinese POS tagging 
Experiments ::: Part-of-Speech Tagging ::: Baselines
We use the following baselines:
Joint-POS: shao2017character jointly learns Chinese word segmentation and POS 
Lattice-LSTM: lattice2018zhang constructs a word-character lattice 
Bert-Tagger: devlin2018bert treats part-of-speech as a tagging task 
Experiments ::: Part-of-Speech Tagging ::: Results
Table presents the experimental results on the POS task  As can be seen, the proposed DSC loss outperforms the best baseline results by a large margin, i e , outperforming BERT-tagger by +1 86 in terms of F1 score on CTB5, +1 80 on CTB6 and +2 19 on UD1 4  As far as we are concerned, we are achieving SOTA performances on the three datasets  Weighted cross entropy and focal loss only gain a little performance improvement on CTB5 and CTB6, and the dice loss obtains huge gain on CTB5 but not on CTB6, which indicates the three losses are not consistently robust in resolving the data imbalance issue  The proposed DSC loss performs robustly on all the three datasets 
Experiments ::: Named Entity Recognition
Named entity recognition (NER) refers to the task of detecting the span and semantic category of entities from a chunk of text  Our implementation uses the current state-of-the-art BERT-MRC model proposed by xiaoya2019ner as a backbone  For English datasets, we use BERT$_\text{Large}$ English checkpoints, while for Chinese we use the official Chinese checkpoints  We report span-level micro-averaged precision, recall and F1-score  Hyperparameters are tuned on the development set of each dataset 
Experiments ::: Named Entity Recognition ::: Datasets
For the NER task, we consider both Chinese datasets, i e , OntoNotes4 0 BIBREF34 and MSRA BIBREF35, and English datasets, i e , CoNLL2003 BIBREF36 and OntoNotes5 0 BIBREF37 
CoNLL2003 is an English dataset with 4 entity types: Location, Organization, Person and Miscellaneous  We followed data processing protocols in BIBREF14 
English OntoNotes5 0 consists of texts from a wide variety of sources and contains 18 entity types  We use the standard train/dev/test split of CoNLL2012 shared task 
Chinese MSRA performs as a Chinese benchmark dataset containing 3 entity types  Data in MSRA is collected from news domain  Since the development set is not provided in the original MSRA dataset, we randomly split the training set into training and development splits by 9:1  We use the official test set for evaluation 
Chinese OntoNotes4 0 is a Chinese dataset and consists of texts from news domain, which has 18 entity types  In this paper, we take the same data split as wu2019glyce did 
Experiments ::: Named Entity Recognition ::: Baselines
We use the following baselines:
ELMo: a tagging model from peters2018deep 
Lattice-LSTM: lattice2018zhang constructs a word-character lattice, only used in Chinese datasets 
CVT: from kevin2018cross, which uses Cross-View Training(CVT) to improve the representations of a Bi-LSTM encoder 
Bert-Tagger: devlin2018bert treats NER as a tagging task 
Glyce-BERT: wu2019glyce combines glyph information with BERT pretraining 
BERT-MRC: The current SOTA model for both Chinese and English NER datasets proposed by xiaoya2019ner, which formulate NER as machine reading comprehension task 
Experiments ::: Named Entity Recognition ::: Results
Table shows experimental results on NER datasets

ground_truth:  The features extracted from CNN.

prompt_front: You are given a scientific article and a question. Answer the question as concisely as you can, using a single phrase or sentence if possible. If the question cannot be answered based on the information in the article, write "unanswerable". If the question is a yes/no question, answer "yes", "no", or "unanswerable". Do not provide any explanation.

Please answer the questions based on the text provided below. How are weights dynamically adjusted?
Context 3:  For English datasets including CoNLL2003 and OntoNotes5 0, our proposed method outperforms BERT-MRCBIBREF38 by +0 29 and +0 96 respectively  We observe huge performance boosts on Chinese datasets, achieving F1 improvements by +0 97 and +2 36 on MSRA and OntoNotes4 0, respectively  As far as we are concerned, we are setting new SOTA performances on all of the four NER datasets 
Experiments ::: Machine Reading Comprehension
Machine reading comprehension (MRC) BIBREF39, BIBREF40, BIBREF41, BIBREF40, BIBREF42, BIBREF15 has become a central task in natural language understanding  MRC in the SQuAD-style is to predict the answer span in the passage given a question and the passage  In this paper, we choose the SQuAD-style MRC task and report Extract Match (EM) in addition to F1 score on validation set  All hyperparameters are tuned on the development set of each dataset 
Experiments ::: Machine Reading Comprehension ::: Datasets
The following five datasets are used for MRC task: SQuAD v1 1, SQuAD v2 0 BIBREF4, BIBREF6 and Quoref BIBREF8 
SQuAD v1 1 and SQuAD v2 0 are the most widely used QA benchmarks  SQuAD1 1 is a collection of 100K crowdsourced question-answer pairs, and SQuAD2 0 extends SQuAD1 1 allowing no short answer exists in the provided passage 
Quoref is a QA dataset which tests the coreferential reasoning capability of reading comprehension systems, containing 24K questions over 4 7K paragraphs from Wikipedia 
Experiments ::: Machine Reading Comprehension ::: Baselines
We use the following baselines:
QANet: qanet2018 builds a model based on convolutions and self-attention  Convolution to model local interactions and self-attention to model global interactions 
BERT: devlin2018bert treats NER as a tagging task 
XLNet: xlnet2019 proposes a generalized autoregressive pretraining method that enables learning bidirectional contexts 
Experiments ::: Machine Reading Comprehension ::: Results
Table shows the experimental results for MRC tasks  With either BERT or XLNet, our proposed DSC loss obtains significant performance boost on both EM and F1  For SQuADv1 1, our proposed method outperforms XLNet by +1 25 in terms of F1 score and +0 84 in terms of EM and achieves 87 65 on EM and 89 51 on F1 for SQuAD v2 0  Moreover, on QuoRef, the proposed method surpasses XLNet results by +1 46 on EM and +1 41 on F1  Another observation is that, XLNet outperforms BERT by a huge margin, and the proposed DSC loss can obtain further performance improvement by an average score above 1 0 in terms of both EM and F1, which indicates the DSC loss is complementary to the model structures 
Experiments ::: Paraphrase Identification
Paraphrases are textual expressions that have the same semantic meaning using different surface words  Paraphrase identification (PI) is the task of identifying whether two sentences have the same meaning or not  We use BERT BIBREF11 and XLNet BIBREF43 as backbones and report F1 score for comparison  Hyperparameters are tuned on the development set of each dataset 
Experiments ::: Paraphrase Identification ::: Datasets
We conduct experiments on two widely used datasets for PI task: MRPC BIBREF44 and QQP 
MRPC is a corpus of sentence pairs automatically extracted from online news sources, with human annotations of whether the sentence pairs are semantically equivalent  The MRPC dataset has imbalanced classes (68% positive, 32% for negative) 
QQP is a collection of question pairs from the community question-answering website Quora  The class distribution in QQP is also unbalanced (37% positive, 63% negative) 
Experiments ::: Paraphrase Identification ::: Results
Table shows the results for PI task  We find that replacing the training objective with DSC introduces performance boost for both BERT and XLNet  Using DSC loss improves the F1 score by +0 58 for MRPC and +0 73 for QQP 
Ablation Studies ::: The Effect of Dice Loss on Accuracy-oriented Tasks
We argue that the most commonly used cross-entropy objective is actually accuracy-oriented, whereas the proposed dice loss (DL) performs as a hard version of F1-score  To explore the effect of the dice loss on accuracy-oriented tasks such as text classification, we conduct experiments on the Stanford Sentiment Treebank sentiment classification datasets including SST-2 and SST-5  We fine-tune BERT$_\text{Large}$ with different training objectives  Experiment results for SST are shown in   For SST-5, BERT with CE achieves 55 57 in terms of accuracy, with DL and DSC losses slightly degrade the accuracy performance and achieve 54 63 and 55 19, respectively  For SST-2, BERT with CE achieves 94 9 in terms of accuracy  The same as SST-5, we observe a slight performance drop with DL and DSC, which means that the dice loss actually works well for F1 but not for accuracy 
Ablation Studies ::: The Effect of Hyperparameters in Tversky index
As mentioned in Section SECREF10, Tversky index (TI) offers the flexibility in controlling the tradeoff between false-negatives and false-positives  In this subsection, we explore the effect of hyperparameters (i e , $\alpha $ and $\beta $) in TI to test how they manipulate the tradeoff  We conduct experiments on the Chinese OntoNotes4 0 NER dataset and English QuoRef MRC dataset to examine the influence of tradeoff between precision and recall  Experiment results are shown in Table   The highest F1 for Chinese OntoNotes4 0 is 84 67 when $\alpha $ is set to 0 6 while for QuoRef, the highest F1 is 68 44 when $\alpha $ is set to 0 4  In addition, we can observe that the performance varies a lot as $\alpha $ changes in distinct datasets, which shows that the hyperparameters $\alpha ,\beta $ play an important role in the proposed method 
Conclusion
In this paper, we alleviate the severe data imbalance issue in NLP tasks  We propose to use dice loss in replacement of the standard cross-entropy loss, which performs as a soft version of F1 score  Using dice loss can help narrow the gap between training objectives and evaluation metrics  Empirically, we show that the proposed training objective leads to significant performance boost for part-of-speech, named entity recognition, machine reading comprehension and paraphrase identification tasks 

ground_truth: One can think $(1-p_{i1})$ as a weight associated with each example, which changes as training proceeds. The intuition of changing $p_{i1}$ to $(1-p_{i1}) p_{i1}$ is to push down the weight of easy examples. For easy examples whose probability are approaching 0 or 1, $(1-p_{i1}) p_{i1}$ makes the model attach significantly less focus to them. Figure FIGREF23 gives gives an explanation from the perspective in derivative: the derivative of $\frac{(1-p)p}{1+(1-p)p}$ with respect to $p$ approaches 0 immediately after $p$ approaches 0, which means the model attends less to examples once they are correctly classified.

associates each training example with a weight in proportion to $(1-p)$, and this weight dynamically changes as training proceeds