Voices of CS: Cheng Chi

Second-year PhD student Cheng Chi talks about how his research on robotic control won a Best Paper Award at RSS 2022

 

In the Columbia Artificial Intelligence and Robotics (CAIR) Lab, Cheng Chi stands in front of a robotic arm. At the end of the arm sits a yellow plastic cup. His goal at the moment is to use a piece of rope to hit the cup to the ground.

“I never thought I would have to do this as part of a research project,” said Chi, a second-year PhD student. He was conducting the exercise to gain a better understanding of physical movement and how it can be applied to a robotic control system.

Existing robotic systems struggle at precisely manipulating objects with complex dynamics, such as hitting a small target with a whip or swinging tablecloths to an exact location. While these tasks are quite hard even for humans, we usually have a good intuition about how to change our actions after a failed attempt, and iteratively get closer to the goal.

Cheng Chi in the CAIR Lab

Chi was able to knock the cup off after five tries. Now, it’s the robot’s turn to fling the piece of rope. It takes the robot four times to hit the target during the experiment (in general less than 10 times). The algorithm/neural network was trained in a simulator using a large amount of data. The robot, called Oolong, had to hit a target and was tested on different kinds of ropes it had never seen before.

Together with Assistant Professor Shuran Song and colleagues from the CAIR Lab, Chi worked to formalize this intuition into an algorithm called Iterative Residual Policy (IRP), a general learning framework for repeatable tasks with complex dynamics where a single model was trained using inaccurate simulation data. IRP can learn from that data and hit many targets with unfamiliar ropes in real robotic experiments, reaching sub-inch accuracy, and demonstrating its strong generalization capability.

This research brings robots from factories, where everything is rigid and can be accurately modeled, closer to everyday households filled with dirty laundry, raw vegetables to be washed in the sink, and leftover food to be cleaned from the fridge. It could potentially alleviate the labor shortage in food, retail, and logistics due to the aging population in many parts of the world. This could also enable the automation of simple tasks like changing a bed sheet and badges in hospitals with infectious disease patients.

The team won a Best Paper Award at the Robot Science and Systems Conference (RSS 2022). We caught up with Chi to find out more about his research and PhD life at Columbia.

Q: How did you become part of the research project?

This is part of a grant from the Toyota Research Institute on deformable object manipulation. For this specific project, I wanted to explore more complex and dynamic forms of robotic manipulation and control. As the primary researcher of this project, I decided on the research topic, problem, and task.

 

Q: How long did you work on the project? What did you have to do, or read to prepare to make the system?

The project started in May 2021. I did a lot of research about control theory for underactuated systems, chaos, and how to work with robot hardware.

Classical robotics literature divides the operation of a robot into three stages — perception, planning, and control. In my previous research, I studied perception and the planning stage of robotics. However, I realized that my knowledge still has a noticeable hole in control theory and systems that control the function and movement of robots.

I believe that I will never become a full-fledged roboticist without understanding all parts of robotic operations. Therefore, I intentionally steered this project toward control which allows me to read more into control-related literature and classes.

For example, I went over the YouTube recording of MIT’s underactuated robotics, taught by Professor Russ Tedrake, who has been known for his contributions to the control of locomotion systems (such as Boston Dynamic’s quadruped robots).

Another interesting thing about control is that, unlike planning, the control of the human body mostly happens at a subconscious level. Therefore, understanding more about control also gave me more insight into how the human body works.

The key realization came after months of reflecting on how I achieved certain tasks and how to formulate such a problem.

Since the relatively early stage of this project (after I decided to tackle the rope whipping task), I had this lingering feeling that being able to adjust the next action based on the error of my previous action is critical for how humans accomplish this task (by observing myself doing it). But I wasn’t able to connect it with math and concrete algorithms.

The next few months were spent playing with data collected in simulations to understand the structure of this task and problem. I often spent a few afternoons a week just staring at my iPad notes, sketching potential algorithms that can solve this task efficiently. Most of them were futile. However, one afternoon in late September, I suddenly came up with the idea that connects my lingering feeling to this concrete algorithm. And the rest was mostly planning out experiments, executing, and verifying results.

 

Q: Why did you decide to do research on robotic control?

I decided on the research project jointly on what is missing in the field and what I wanted to learn. For example, I wanted to get into control last summer, so I took classes online and read relevant papers to build a foundation. I noticed that the missing piece in the field is deformable manipulation with precision.

Existing robotic algorithms often assume the object being manipulated is rigid, and ignore its physics/dynamics, due to its complexity. My research thrust has been targeting this complexity (of object physics and non-rigidity) head-on, which hopefully will result in better algorithms that will improve the overall performance and robustness of robotics systems, outside of confined/structured industrial environments.

Whipping a piece of rope is one of the simplest instances of dynamic deformable object manipulation, without the additional perceptive complexity such as self-occlusion, etc. However, we believe that whipping a piece of rope and tablecloth is representative of the class of problem we are interested in and that there is no existing robotic system/algorithm that can accomplish this task. Therefore, our algorithm has expanded what is considered possible in robotics.

I thought that it would be cool to simplify it to a minimum-working task, like whipping. Whipping a piece of rope or cloth accurately requires adapting existing skills which humans are good at but it is very difficult for robots to do.

Humans can hit targets with reasonable accuracy after usually 10~20 trials. The best algorithm before IRP takes 100-1000+ trials to get there.

The project spanned 10 months and it was not easy, since solving this novel and challenging task requires going beyond the common paradigm in the field, for example, reinforcement learning or system identification.

I tried three ideas at first and none of them worked or advanced the field to a satisfying degree for me. The final idea was inspired by some studies from the biomechanics/neural science community that I came across while doing research.

While I was struggling with this project, my advisor pointed me to this recording of an RSS 2020 workshop. I was fascinated by one of the talks by Professor Dagmar Stenard and her findings from the biomechanical perspective of how humans minimize uncertainty and avoid the chaotic region of the state space when taking actions.

I read further into her publications and was pleasantly surprised that her group was studying the same rope whipping problem. Their algorithm was crude and they only tested in simulation with many additional assumptions, but I really liked their problem formulation of the whipping task and their use of action primitive, which dramatically reduced the number of parameters needed to describe the dynamic and continuous robot action.

They also demonstrated that their action primitives (that bio literature believes humans also use) are sufficient for this task. Therefore, I took their problem formulation and tweaked their action primitive to better fit real robotic hardware, and eventually developed the IRP algorithm on top of that.

Q: Why did you decide to use different kinds of ropes for the project?

The type of rope we simulated for training is modeled after a thick cotton rope we bought on Amazon. However, due to the various complex physical properties and their effects, the rope modeled in simulation behaves significantly differently from its real-world counterpart. This is an instance of a well-known challenge in the robotics community called “sim2real gap”.

Since the deep-learning revolution (~2014), a large body of robotic algorithms emerged that have shown very promising results in simulated environments. However, they also rely on a large amount of data for training (our algorithm included), which is only feasible to collect in simulation. If the behavior of objects in simulation matches exactly their counterparts in real life, in theory, we can directly apply these data-hungry algorithms to the real world. Unfortunately, this is far from the truth, and the difference is especially big for deformable objects.

The biggest contribution of this paper is providing a solution to close this “sim2real gap” for a limited class of problems (where the actions are repeatable, and the objects can be reset to the original state), i.e. the algorithm behaves just as good in the real world as in simulation, despite the simulation it was trained on is very “wrong”.

To further demonstrate how “wrong” the simulation can be while the algorithm still works, we cut out a long strip of cloth, that behaves like a gymnastic ribbon and treated it as the rope. We also bought a very thick leather bullwhip, that has a non-uniform density (it becomes thinner and thinner as it goes toward the tip), while all ropes we trained in simulation have uniform thickness and density. The experimental results on these two “ropes” were just as good.

Q: What do you think is the most interesting thing about doing research?

I like how researchers are able to try high-risk ideas that actually advance the field and also learn fundamental knowledge about the field. Working in industry usually constrains research options to low-risk ideas, while the engineering effort might be larger.

 

Q: How did your previous experiences prepare you for a PhD?

I gained my initial research experience during my undergrad at the University of Michigan, working on deformable object perception. I had multiple internships, as well as full-time jobs at autonomous vehicle companies, which taught me how to properly engineer a robotics software system.

 

Q: Why did you apply to Columbia and how was that process?

I applied to Columbia to work with Assistant Professor Shuran Song. Just before I graduated from undergrad, Shuran did a job talk at the University of Michigan. My undergrad research advisor Professor Dmitry Berenson was at her talk and he was really impressed. Berenson strongly recommended that I apply to work with her and he thought we would be a great fit. After researching her past publications, I did find a large overlap in our research interests and I only heard good words about her after asking other people who have worked with her.

At the time, I wasn’t really sure about getting a PhD, and because of the time needed to complete the applications, I only applied to two schools. The application website could have been improved, but the overall process is surprisingly smooth. I really like the idea that students are admitted by and to individual professors, and the professors make the decision.

 

Q: What has been the highlight of your time at Columbia?

The highlight of my time is being able to be taught and guided by my advisor, as well as other PhD students.

 

Q: You are starting the third year of your PhD at Columbia, do you think your skills have improved? In which ways?

I think what improved the most was to think more structurally and not be buried by the details. Due to the engineering complexity of robotic systems, there are thousands of variables and decisions, large and small, I needed to make for the project to progress. For example, on the high level, how to model the rope in the simulation, how to model the robot, how to represent the observation and actions, how the model should be architected, etc.

For an inexperienced researcher like myself, it is not obvious which one of these parameters will make or break the project, or will only yield a small change in the final performance. So, I over-analyzed, over-engineered, and over-thought the small problems. Fortunately, Shuran often called out that some of these decisions probably don’t matter that much, and choosing an arbitrary path to go forward is strictly better than spending time thinking about which one is better.

The problem is that this is mostly based on intuition. Shuran can’t always give evidence of why one thing doesn’t matter and why another does. But fortunately, I think I am getting a better grasp of these intuitions. It will become easier for me as time passes and I become an expert in robotics.

I also have found that it is really important to communicate clearly, both in meetings and when writing things down for reports or even emails. Learning by example from my advisor also helps a lot.

 

Q: What is your advice to students on how to navigate their time at Columbia? If they want to do research what should they know or do to prepare?

New students going into research should try as hard as possible to push through the first research project. It is always hard in the beginning, and it might feel impossible, but you can do it. Build up a tolerance for failure and continue to try different things, which is often critical to making a contribution to the field.

 

 

5 Research Papers Accepted to ICML 2022

Papers from CS researchers have been accepted to the 38th International Conference on Machine Learning (ICML 2021)

Below are the abstracts and links to the accepted papers.

 

Simple And Near-Optimal Algorithms For Hidden Stratification And Multi-Group Learning
Christopher Tosh Memorial Sloan Kettering Cancer Center, Daniel Hsu Columbia University

Abstract
Multi-group agnostic learning is a formal learning criterion that is concerned with the conditional risks of predictors within subgroups of a population. The criterion addresses recent practical concerns such as subgroup fairness and hidden stratification. This paper studies the structure of solutions to the multi-group learning problem and provides simple and near-optimal algorithms for the learning problem.

 

On Measuring Causal Contributions Aia Do-Interventions
Yonghan Jung Purdue University, Shiva Kasiviswanathan Amazon, Jin Tian Iowa State University, Dominik Janzing Amazon, Patrick Bloebaum Amazon, Elias Bareinboim Columbia University

Abstract
Causal contributions measure the strengths of different causes to a target quantity. Understanding causal contributions is important in empirical sciences and data-driven disciplines since it allows to answer practical queries like “what are the contributions of each cause to the effect?” In this paper, we develop a principled method for quantifying causal contributions. First, we provide desiderata of properties (axioms) that causal contribution measures should satisfy and propose the do-Shapley values (inspired by do-interventions (Pearl, 2000)) as a unique method satisfying these properties. Next, we develop a criterion under which the do-Shapley values can be efficiently inferred from non-experimental data. Finally, we provide do-Shapley estimators exhibiting consistency, computational feasibility, and statistical robustness. Simulation results corroborate with the theory.

 

Partial Counterfactual Identification From Observational And Experimental Data
Junzhe Zhang Columbia University, Jin TianIowa Iowa State University, Elias Bareinboim Columbia University

Abstract
This paper investigates the problem of bounding counterfactual queries from an arbitrary collection of observational and experimental distributions and qualitative knowledge about the underlying data-generating model represented in the form of a causal diagram. We show that all counterfactual distributions in an arbitrary structural causal model (SCM) with discrete observed domains could be generated by a canonical family of SCMs with the same causal diagram where unobserved (exogenous) variables are also discrete, taking values in finite domains. Utilizing the canonical SCMs, we translate the problem of bounding counterfactuals into that of polynomial programming whose solution provides optimal bounds for the counterfactual query. Solving such polynomial programs is in general computationally expensive. We then develop effective Monte Carlo algorithms to approximate optimal bounds from a combination of observational and experimental data. Our algorithms are validated extensively on synthetic and real-world datasets.

 

Counterfactual Transportability: A Formal Approach
Juan D. Correa Universidad Autonoma de Manizales, Sanghack Lee Seoul National University, Elias Bareinboim Columbia University

Abstract
Generalizing causal knowledge across environments is a common challenge shared across many of the data-driven disciplines, including AI and ML. Experiments are usually performed in one environment (e.g., in a lab, on Earth, in a training ground), almost invariably, with the intent of being used elsewhere (e.g., outside the lab, on Mars, in the real world), in an environment that is related but somewhat different than the original one, where certain conditions and mechanisms are likely to change. This generalization task has been studied in the causal inference literature under the rubric of transportability (Pearl and Bareinboim, 2011). While most transportability works focused on generalizing associational and interventional distributions, the generalization of counterfactual distributions has not been formally studied. In this paper, we investigate the transportability of counterfactuals from an arbitrary combination of observational and experimental distributions coming from disparate domains. Specifically, we introduce a sufficient and necessary graphical condition and develop an efficient, sound, and complete algorithm for transporting counterfactual quantities across domains in nonparametric settings. Failure of the algorithm implies the impossibility of generalizing the target counterfactual from the available data without further assumptions.

 

Variational Inference for Infinitely Deep Neural Networks
Achille Nazaret Columbia University, David Blei Columbia University

Abstract
We introduce the unbounded depth neural network (UDN), an infinitely deep probabilistic model that adapts its complexity to the training data. The UDN contains an infinite sequence of hidden layers and places an unbounded prior on a truncation ℓ, the layer from which it produces its data. Given a dataset of observations, the posterior UDN provides a conditional distribution of both the parameters of the infinite neural network and its truncation. We develop a novel variational inference algorithm to approximate this posterior, optimizing a distribution of the neural network weights and of the truncation depth ℓ, and without any upper limit on ℓ. To this end, the variational family has a special structure: it models neural network weights of arbitrary depth, and it dynamically creates or removes free variational parameters as its distribution of the truncation is optimized. (Unlike heuristic approaches to model search, it is solely through gradient-based optimization that this algorithm explores the space of truncations.) We study the UDN on real and synthetic data. We find that the UDN adapts its posterior depth to the dataset complexity; it outperforms standard neural networks of similar computational complexity; and it outperforms other approaches to infinite-depth neural networks.

 

Software Systems Laboratory Wins Best Paper Award at OSDI 2022

Members of the Software Systems Laboratory
Members of the Software Systems Laboratory

Researchers from the Software Systems Laboratory bagged a Best Paper Award at the 16th USENIX Symposium on Operating Systems Design and Implementation (OSDI 2021). OSDI is “a premier forum for discussing the design, implementation, and implications of systems software.” A total of six research papers from the department were accepted to the conference.

 

Jay Lepreau Best Paper Award, OSDI’22

XRP: In-Kernel Storage Functions with eBPF
Yuhong Zhong Columbia University, Haoyu Li Columbia University, Yu Jian Wu Columbia University, Ioannis Zarkadas Columbia University, Jeffrey Tao Columbia University, Evan Mesterhazy Columbia University, Michael Makris Columbia University, Junfeng Yang Columbia University, Amy Tai Google, Ryan Stutsman University of Utah; Asaf Cidon Columbia University

Abstract:
With the emergence of microsecond-scale NVMe storage devices, the Linux kernel storage stack overhead has become significant, almost doubling access times. We present XRP, a framework that allows applications to execute user-defined storage functions, such as index lookups or aggregations, from an eBPF hook in the NVMe driver, safely bypassing most of the kernel’s storage stack. To preserve file system semantics, XRP propagates a small amount of kernel state to its NVMe driver hook where the user-registered eBPF functions are called. We show how two key-value stores, BPF-KV, a simple B+-tree key-value store, and WiredTiger, a popular log-structured merge tree storage engine, can leverage XRP to significantly improve throughput and latency.

 

ROLLER: Fast and Efficient Tensor Compilation for Deep Learning
Hongyu Zhu University of Toronto and Microsoft Research; Ruofan Wu Renmin University of China and Microsoft Research; Yijia Diao Shanghai Jiao Tong University and Microsoft Research, Shanbin Ke UCSD and Microsoft Research, Haoyu Li Columbia University and Microsoft Research; Chen Zhang Tsinghua University and Microsoft Research; Jilong Xue Microsoft Research, Lingxiao Ma Microsoft Research, Yuqing Xia Microsoft Research, Wei Cui Microsoft Research, Fan Yang Microsoft Research, Mao Yang Microsoft Research, Lidong Zhou Microsoft Research, Asaf Cidon Columbia University, Gennady Pekhimenko University of Toronto

Abstract:
Despite recent advances in tensor compilers, it often costs hours to generate an efficient kernel for an operator, a compute-intensive sub-task in a deep neural network (DNN), on various accelerators (e.g., GPUs). This significantly slows down DNN development cycles and incurs heavy burdens on the development of general kernel libraries and custom kernels, especially for new hardware vendors. The slow compilation process is due to the large search space formulated by existing DNN compilers, which have to use machine learning algorithms to find good solutions.


In this paper, we present ROLLER, which takes a different construction-based approach to generate kernels. At the core of ROLLER is rTile, a new tile abstraction that encapsulates tensor shapes that align with the key features of the underlying accelerator, thus achieving efficient execution by limiting the shape choices. ROLLER then adopts a recursive rTile-based construction algorithm to generate rTile-based programs (rProgram), whose performance can be evaluated efficiently with a micro-performance model without being evaluated in a real device. As a result, ROLLER can generate efficient kernels in seconds, with comparable performance to the state-of-the-art solutions on popular accelerators like GPUs, while offering better kernels on less mature accelerators like IPUs.

 

Design and Verification of the Arm Confidential Compute Architecture
Xupeng Li Columbia University, Xuheng Li Columbia University, Christoffer Dall Arm Ltd, Ronghui Gu Columbia University, Jason Nieh Columbia University, Yousuf Sait Arm Ltd, Gareth Stockwell Arm Ltd

Abstract:
The increasing use of sensitive private data in computing is matched by a growing concern regarding data privacy. System software such as hypervisors and operating systems are supposed to protect and isolate applications and their private data, but their large codebases contain many vulnerabilities that can risk data confidentiality and integrity. We introduce Realms, a new abstraction for confidential computing to protect the data confidentiality and integrity of virtual machines. Hardware creates and enforces Realm world, a new physical address space for Realms. Firmware controls the hardware to secure Realms and handles requests from untrusted system software to manage Realms, including creating and running them. Untrusted system software retains control of the dynamic allocation of memory to Realms, but cannot access Realm memory contents, even if run at a higher privileged level. To guarantee the security of Realms, we verified the firmware, introducing novel verification techniques that enable us to prove, for the first time, the security and correctness of concurrent software with hand-over-hand locking and dynamically allocated shared page tables, data races in kernel code running on relaxed memory hardware, integrated C and Arm assembly code calling one another, and untrusted software being in full control of allocating system resources. Realms are included in the Arm Confidential Compute Architecture.

 

DuoAI: Fast, Automated Inference of Inductive Invariants for Verifying Distributed Protocols
Jianan Yao Columbia University, Runzhou Tao Columbia University, Ronghui Gu Columbia University, Jason Nieh Columbia University

Abstract:
Distributed systems are complex and difficult to build correctly. Formal verification can provably rule out bugs in such systems, but finding an inductive invariant that implies the safety property of the system is often the hardest part of the proof. We present DuoAI, an automated system that quickly finds inductive invariants for verifying distributed protocols by reducing SMT query costs in checking invariants with existential quantifiers. DuoAI enumerates the strongest candidate invariants that hold on validate states from protocol simulations, then applies two methods in parallel, returning the result from the method that succeeds first. One checks all candidate invariants and weakens them as needed until it finds an inductive invariant that implies the safety property. Another checks invariants without existential quantifiers to find an inductive invariant without the safety property, then adds candidate invariants with existential quantifiers to strengthen it until the safety property holds. Both methods are guaranteed to find an inductive invariant that proves desired safety properties, if one exists, but the first reduces SMT query costs when more candidate invariants with existential quantifiers are needed, while the second reduces SMT query costs when few candidate invariants with existential quantifiers suffice. We show that DuoAI verifies more than two dozen common distributed protocols automatically, including various versions of Paxos, and outperforms alternative methods both in the number of protocols it verifies and the speed at which it does so, including solving Paxos more than two orders of magnitude faster than previous methods.

 

BlackBox: A Container Security Monitor for Protecting Containers on Untrusted Operating Systems
Alexander Van’t Hof Columbia University, Jason Nieh Columbia University

Abstract:
Containers are widely deployed to package, isolate, and multiplex applications on shared computing infrastructure, but rely on the operating system to enforce their security guarantees. This poses a significant security risk as large operating system codebases contain many vulnerabilities. We have created BlackBox, a new container architecture that provides fine-grain protection of application data confidentiality and integrity without trusting the operating system. BlackBox introduces a container security monitor, a small trusted computing base that creates protected physical address spaces (PPASes) for each container such that there is no direct information flow from container to operating system or other container PPASes. Indirect information flow can only happen through the monitor, which only copies data between container PPASes and the operating system as system call arguments, encrypting data as needed to protect interprocess communication through the operating system. Containerized applications do not need to be modified, can still make use of operating system services via system calls, yet their CPU and memory state are isolated and protected from other containers and the operating system. We have implemented BlackBox by leveraging Arm hardware virtualization support, using nested paging to enforce PPASes. The trusted computing base is a few thousand lines of code, many orders of magnitude less than Linux, yet supports widely-used Linux containers with only modest modifications to the Linux kernel. We show that BlackBox provides superior security guarantees over traditional hypervisor and container architectures with only modest performance overhead on real application workloads.

 

UPGRADVISOR: Early Adopting Dependency Updates Using Hybrid Program Analysis and Hardware Tracing
Yaniv David Columbia University, Xudong Sun Nanjing University, Raphael J. Sofaer Columbia University, Aditya Senthilnathan IIT, Delhi, Junfeng Yang Columbia University, Zhiqiang Zuo Nanjing University, Guoqing Harry Xu UCLA, Jason Nieh Columbia University, Ronghui Gu Columbia University

Abstract:
Applications often have fast-paced release schedules, but adoption of software dependency updates can lag by years, leaving applications susceptible to security risks and unexpected breakage. To address this problem, we present UPGRADVISOR, a system that reduces developer effort in evaluating dependency updates and can, in many cases, automatically determine which updates are backward-compatible versus API-breaking. UPGRADVISOR introduces a novel co-designed static analysis and dynamic tracing mechanism to gauge the scope and effect of dependency updates on an application. Static analysis prunes changes irrelevant to an application and clusters relevant ones into targets. Dynamic tracing needs to focus only on whether targets affect an application, making it fast and accurate. UPGRADVISOR handles dynamic interpreted languages and introduces call graph over-approximation to account for their lack of type information and selective hardware tracing to capture program execution while ignoring interpreter machinery.

We have implemented UPGRADVISOR for Python and evaluated it on 172 dependency updates previously blocked from being adopted in widely-used open-source software, including Django, aws-cli, tfx, and Celery. UPGRADVISOR automatically determined that 56% of dependencies were safe to update and reduced by more than an order of magnitude the number of code changes that needed to be considered by dynamic tracing. Evaluating UPGRADVISOR’s tracer in a production-like environment incurred only 3% overhead on average, making it fast enough to deploy in practice. We submitted safe updates that were previously blocked as pull requests for nine projects, and their developers have already merged most of them.

 

6 Papers from CS Researchers Accepted to NAACL 2022

Researchers from the department presented natural language processing (NLP) papers at the 2022 Annual Conference of the North American Chapter of the Association for Computational Linguistics (NAACL 2022).

Selective Differential Privacy for Language Models
Weiyan Shi, Aiqi Cui, Evan Li, Ruoxi Jia, Zhou Yu

With the increasing applications of language models, it has become crucial to protect these models from leaking private information. Previous work has attempted to tackle this challenge by training RNN-based language models with differential privacy guarantees. However, applying classical differential privacy to language models leads to poor model performance as the underlying privacy notion is over-pessimistic and provides undifferentiated protection for all tokens in the data. Given that the private information in natural language is sparse (for example, the bulk of an email might not carry personally identifiable information), we propose a new privacy notion, selective differential privacy, to provide rigorous privacy guarantees on the sensitive portion of the data to improve model utility. To realize such a new notion, we develop a corresponding privacy mechanism, Selective-DPSGD, for RNN-based language models. Besides language modeling, we also apply the method to a more concrete application–dialog systems. Experiments on both language modeling and dialog system building show that the proposed privacy-preserving mechanism achieves better utilities while remaining safe under various privacy attacks compared to the baselines. The data and code are released at this HTTPS URL to facilitate future research.

Knowledge-Grounded Dialogue Generation with a Unified Knowledge Representation
Yu Li, Baolin Peng, Yelong Shen, Yi Mao, Lars Liden, Zhou Yu, Jianfeng Gao

Knowledge-grounded dialogue systems are challenging to build due to the lack of training data and heterogeneous knowledge sources. Existing systems perform poorly on unseen topics due to limited topics covered in the training data. In addition, heterogeneous knowledge sources make it challenging for systems to generalize to other tasks because knowledge sources in different knowledge representations require different knowledge encoders. To address these challenges, we present PLUG, a language model that homogenizes different knowledge sources to a unified knowledge representation for knowledge-grounded dialogue generation tasks. PLUG is pre-trained on a dialogue generation task conditioned on a unified essential knowledge representation. It can generalize to different downstream knowledge-grounded dialogue generation tasks with a few training examples. The empirical evaluation on two benchmarks shows that our model generalizes well across different knowledge-grounded tasks. It can achieve comparable performance with state-of-the-art methods under a fully-supervised setting and significantly outperforms other methods in zero-shot and few-shot settings.

Database Search Results Disambiguation for Task-Oriented Dialog Systems
Kun Qian, Ahmad Beirami, Satwik Kottur, Shahin Shayandeh, Paul Crook, Alborz Geramifard, Zhou Yu, Chinnadhurai Sankar

As task-oriented dialog systems are becoming increasingly popular in our lives, more realistic tasks have been proposed and explored. However, new practical challenges arise. For instance, current dialog systems cannot effectively handle multiple search results when querying a database, due to the lack of such scenarios in existing public datasets. In this paper, we propose Database Search Result (DSR) Disambiguation, a novel task that focuses on disambiguating database search results, which enhances user experience by allowing them to choose from multiple options instead of just one. To study this task, we augment the popular task-oriented dialog datasets (MultiWOZ and SGD) with turns that resolve ambiguities by (a) synthetically generating turns through a pre-defined grammar, and (b) collecting human paraphrases for a subset. We find that training on our augmented dialog data improves the model’s ability to deal with ambiguous scenarios, without sacrificing performance on unmodified turns. Furthermore, pre-fine tuning and multi-task learning help our model to improve performance on DSRdisambiguation even in the absence of indomain data, suggesting that it can be learned as a universal dialog skill. Our data and code will be made publicly available.

ErAConD: Error Annotated Conversational Dialog Dataset for Grammatical Error Correction
Xun Yuan, Sam Pham, Sam Davidson, Zhou Yu

Currently available grammatical error correction (GEC) datasets are compiled using well-formed written text, limiting the applicability of these datasets to other domains such as informal writing and dialog. In this paper, we present a novel parallel GEC dataset drawn from open-domain chatbot conversations; this dataset is, to our knowledge, the first GEC dataset targeted to a conversational setting. To demonstrate the utility of the dataset, we use our annotated data to fine-tune a state-of-the-art GEC model, resulting in a 16-point increase in model precision. This is of particular importance in a GEC model, as model precision is considered more important than recall in GEC tasks since false positives could lead to serious confusion in language learners. We also present a detailed annotation scheme which ranks errors by perceived impact on comprehensibility, making our dataset both reproducible and extensible. Experimental results show the effectiveness of our data in improving GEC model performance in conversational scenarios.

Improving Conversational Recommendation Systems’ Quality with Context-Aware Item Meta-Information
Bowen Yang, Cong Han, Yu Li, Lei Zuo, Zhou Yu

Conversational recommendation systems (CRS) engage with users by inferring user preferences from dialog history, providing accurate recommendations, and generating appropriate responses. Previous CRSs use knowledge graph (KG) based recommendation modules and integrate KG with language models for response generation. Although KG-based approaches prove effective, two issues remain to be solved. First, KG-based approaches ignore the information in the conversational context but only rely on entity relations and bag of words to recommend items. Second, it requires substantial engineering efforts to maintain KGs that model domain-specific relations, thus leading to less flexibility. In this paper, we propose a simple yet effective architecture comprising a pre-trained language model (PLM) and an item metadata encoder. The encoder learns to map item metadata to embeddings that can reflect the semantic information in the dialog context. The PLM then consumes the semantic-aligned item embeddings together with dialog context to generate high-quality recommendations and responses. Instead of modeling entity relations with KGs, our model reduces engineering complexity by directly converting each item to an embedding. Experimental results on the benchmark dataset ReDial show that our model obtains state-of-the-art results on both recommendation and response generation tasks.

Differentially private decoding in large language models
By Jimit Majmudar, Christophe Dupuy, Charith Peris, Sami Smaili, Rahul Gupta, Richard Zemel


Recent large-scale natural language processing (NLP) systems use a pre-trained Large Language Model (LLM) on massive and diverse corpora as a headstart. In practice, the pre-trained model is adapted to a wide array of tasks via fine-tuning on task-specific datasets. LLMs, while effective, have been shown to memorize instances of training data thereby potentially revealing private information processed during pre-training. The potential leakage might further propagate to the downstream tasks for which LLMs are fine-tuned. On the other hand, privacy-preserving algorithms usually involve retraining from scratch, which is prohibitively expensive for LLMs. In this work, we propose a simple, easy to interpret, and computationally lightweight perturbation mechanism to be applied to an already trained model at the decoding stage. Our perturbation mechanism is model-agnostic and can be used in conjunction with any LLM. We provide a theoretical analysis showing that the proposed mechanism is differentially private, and experimental results show a privacy-utility trade-off.