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Deep neural networks are vulnerable to a range of adversaries. A particularly pernicious class of vulnerabilities are backdoors, where model predictions diverge in the presence of subtle triggers in inputs. An attacker can implant a backdoor by poisoning the training data to yield a desired target prediction on triggered inputs. We study backdoors in the context of deep-learning for source code. (1) We define a range of backdoor classes for source-code tasks and show how to poison a dataset to install such backdoors. (2) We adapt and improve recent algorithms from robust statistics for our setting, showing that backdoors leave a spectral signature in the learned representation of source code, thus enabling detection of poisoned data. (3) We conduct a thorough evaluation on different architectures and languages, showing the ease of injecting backdoors and our ability to eliminate them.

IJCNLP-AACL 2021

Backdoors in Neural Models of Source Code

spectral signatures

source code

backdoor attack

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The great event is jointly organized by the Association for Computational Linguistics (ACL) and Asian Federation of Natural Language Processing (AFNLP).

workshop paper

Although parsing to Abstract Meaning Representation (AMR) has become very popular and AMR has been shown effective on the many sentence-level downstream tasks, little work has studied how to generate AMRs that can represent multi-sentence information.
We introduce the first end-to-end AMR coreference resolution model in order to build multi-sentence AMRs.
Compared with the previous pipeline and rule-based approaches, our model alleviates error propagation and it is more robust for both in-domain and out-domain situations.
Besides, the document-level AMRs obtained by our model can significantly improve over the AMRs generated by a rule-based method (Liu et al., 2015) on text summarization.

End-to-End AMR Corefencence Resolution

Transformer language models have shown remarkable ability in detecting when a word is anomalous in context, but likelihood scores offer no information about the cause of the anomaly. In this work, we use Gaussian models for density estimation at intermediate layers of three language models (BERT, RoBERTa, and XLNet), and evaluate our method on BLiMP, a grammaticality judgement benchmark. In lower layers, surprisal is highly correlated to low token frequency, but this correlation diminishes in upper layers. Next, we gather datasets of morphosyntactic, semantic, and commonsense anomalies from psycholinguistic studies; we find that the best performing model RoBERTa exhibits surprisal in earlier layers when the anomaly is morphosyntactic than when it is semantic, while commonsense anomalies do not exhibit surprisal at any intermediate layer. These results suggest that language models employ separate mechanisms to detect different types of linguistic anomalies.

How is BERT surprised? Layerwise detection of linguistic anomalies

Most of the recent work on personality detection from online posts adopts multifarious deep neural networks to represent the posts and builds predictive models in a data-driven manner, without the exploitation of psycholinguistic knowledge that may unveil the connections between one's language use and his psychological traits. In this paper, we propose a psycholinguistic knowledge-based tripartite graph network, TrigNet, which consists of a tripartite graph network and a BERT-based graph initializer. The graph network injects structural psycholinguistic knowledge in LIWC, a computerized instrument for psycholinguistic analysis, by constructing a heterogeneous tripartite graph. The initializer is employed to provide initial embeddings for the graph nodes. To reduce the computational cost in graph learning, we further propose a novel flow graph attention network (GAT) that only transmits messages between neighboring parties in the tripartite graph. Benefiting from the tripartite graph, TrigNet can aggregate post information from a psychological perspective, which is a novel way of exploiting domain knowledge. Extensive experiments on two datasets show that TrigNet outperforms the existing state-of-art model by 3.47 and 2.10 points in average F1. Moreover, the flow GAT reduces the FLOPS and Memory measures by 38% and 32%, respectively, in comparison to the original GAT in our setting.

Psycholinguistic Tripartite Graph Network for Personality Detection

Correct natural language understanding requires computers to distinguish the literal and metaphorical senses of a word. Recent neu- ral models achieve progress on verb metaphor detection by viewing it as sequence labeling. In this paper, we argue that it is appropriate to view this task as relation classification between a verb and its various contexts. We propose the Metaphor-relation BERT (Mr-BERT) model, which explicitly models the relation between a verb and its grammatical, sentential and semantic contexts. We evaluate our method on the VUA, MOH-X and TroFi datasets. Our method gets competitive results compared with state-of-the-art approaches.

Verb Metaphor Detection via Contextual Relation Learning

Pretraining and multitask learning are widely used to improve the speech translation performance. In this study, we are interested in training a speech translation model along with an auxiliary text translation task. We conduct a detailed analysis to understand the impact of the auxiliary task on the primary task within the multitask learning framework. Our analysis confirms that multitask learning tends to generate similar decoder representations from different modalities and preserve more information from the pretrained text translation modules. We observe minimal negative transfer effect between the two tasks and sharing more parameters is helpful to transfer knowledge from the text task to the speech task. The analysis also reveals that the modality representation difference at the top decoder layers is still not negligible, and those layers are critical for the translation quality. Inspired by these findings, we propose three methods to improve translation quality. First, a parameter sharing and initialization strategy is proposed to enhance information sharing between the tasks. Second, a novel attention-based regularization is proposed for the encoders and pulls the representations from different modalities closer. Third, an online knowledge distillation is proposed to enhance the knowledge transfer from the text to the speech task. Our experiments show that the proposed approach improves translation performance by more than 2 BLEU over a strong baseline and achieves state-of-the-art results on the MuST-C English-German, English-French and English-Spanish language pairs.

Improving Speech Translation by Understanding and Learning from the Auxiliary Text Translation Task

Large pre-trained language models (PTLMs) have been shown to carry biases towards different social groups which leads to the reproduction of stereotypical and toxic content by major NLP systems.
We propose a method based on logistic regression classifiers to probe English, French, and Arabic PTLMs and quantify the potentially harmful content that they convey with respect to a set of templates. The templates are prompted by a name of a social group followed by a cause-effect relation. We use PTLMs to predict masked tokens at the end of a sentence in order to examine how likely they enable toxicity towards specific communities. We shed the light on how such negative content can be triggered within unrelated and benign contexts based on evidence from a large-scale study, then we explain how to take advantage of our methodology to assess and mitigate the toxicity transmitted by PTLMs.

Probing Toxic Content in Large Pre-Trained Language Models

Neural language models can be successfully trained on source code, leading to applications such as code completion. However, their versatile autoregressive self-supervision objective overlooks important global sequence-level features that are present in the data such as syntactic correctness or compilability. In this work, we pose the problem of learning to generate compilable code as constraint satisfaction. We define an Energy-Based Model (EBM) representing a pre-trained generative model with an imposed constraint of generating only compilable sequences. We then use the KL-Adaptive Distributional Policy Gradient algorithm (Khalifa et al., 2021) to train a generative model approximating the EBM. We conduct experiments showing that our pro- posed approach is able to improve compilability rates without sacrificing diversity and complexity of the generated samples.

Energy-Based Models for Code Generation under Compilability Constraints

Many database users do not precisely know the structure or the content of databases, and thus their queries do not exactly reflect their information needs. To help users formulate their questions when they query databases, we propose AUTO SQL, a question auto-completion framework in Text-to-SQL for natural language interfaces to databases. We construct a benchmark dataset and experiment with models on our constructed dataset. Experiment results demonstrate that our dataset is challenging for current models.

AutoSQL: Question Auto-Completion for Text-to-SQL

Translating natural language texts into ex-ecutable scenarios is a very active researcharea, with plenty of applications in the de-velopment of dialogue systems, digital as-sistants, and so on. Crowd-sourcing isnowadays the preferred method for label-ing task-specific executable data, but thebiggest challenge in using crowd-sourcingfor the labeling of executable programs isthat the ramp-up effort required for the an-notators to generate high-quality executa-bles is essentially unattainable.In thiswork we suggest an innovative approachfor modeling and labeling sequential pro-grams, by representing them as a tem-poral sequence of grounded world-states,depicted by the annotator to indicate theresulting world-state for each instruction.Our main innovation is in developing aschedule-like interface that facilitates theannotation of the sequence of world-states,which can then be deterministically trans-formed to the out-coming executable. Wedemonstrate this approach for the domainof recipe parsing, for understanding andexecuting the instructions in a kitchen-likeenvironment.This approach is entirelygeneral and can be also applied to otherdomains, e.g., the coding and execution ofUI instructions or WetLab protocols.

Don’t code, schedule! Annotating Instructional Executable Text at Scale Without Teaching Annotators How to Code

In this paper, we present a deep learning code completion model for the R programming language.
We introduce several techniques to utilize language modeling based architecture in the code completion task.
With these techniques, the model requires low resources, but still achieves high quality.

We also present an evaluation dataset for the R programming language completion task.
Our dataset contains multiple autocompletion usage contexts and that provides robust validation results. The dataset is publicly available.

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Backdoors in Neural Models of Source Code

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End-to-End AMR Corefencence Resolution

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