Liwen Sun, James Jialun Zhao, Wenjing Han, Chenyan Xiong. Proceedings of the 2025 Conference of the Nations of the Americas Chapter of the Association for Computational Linguistics: Human Language Technologies (Volume 1: Long Papers). 2025.

In the emergency department (ED), patients undergo triage and multiple laboratory tests before diagnosis. This time-consuming process causes ED crowding which impacts patient mortality, medical errors, staff burnout, etc. This work proposes (time) cost-effective diagnostic assistance that leverages artificial intelligence systems to help ED clinicians make efficient and accurate diagnoses. In collaboration with ED clinicians, we use public patient data to curate MIMIC-ED-Assist, a benchmark for AI systems to suggest laboratory tests that minimize wait time while accurately predicting critical outcomes such as death. With MIMIC-ED-Assist, we develop ED-Copilot which sequentially suggests patient-specific laboratory tests and makes diagnostic predictions. ED-Copilot employs a pre-trained bio-medical language model to encode patient information and uses reinforcement learning to minimize ED wait time and maximize prediction accuracy. On MIMIC-ED-Assist, ED-Copilot improves prediction accuracy over baselines while halving average wait time from four hours to two hours. ED-Copilot can also effectively personalize treatment recommendations based on patient severity, further highlighting its potential as a diagnostic assistant. Since MIMIC-ED-Assist is a retrospective benchmark, ED-Copilot is restricted to recommend only observed tests. We show ED-Copilot achieves competitive performance without this restriction as the maximum allowed time increases. Our code is available at https://github.com/cxcscmu/ED-Copilot.

Cloud object stores such as Amazon S3 are some of the largest and most cost-effective storage systems on the planet, making them an attractive target to store large data warehouses and data lakes. Unfortunately, their implementation as key-value stores makes it difficult to achieve ACID transactions and high performance: metadata operations such as listing objects are expensive, and consistency guarantees are limited. In this paper, we present Delta Lake, an open source ACID table storage layer over cloud object stores initially developed at Databricks. Delta Lake uses a transaction log that is compacted into Apache Parquet format to provide ACID properties, time travel, and significantly faster metadata operations for large tabular datasets (e.g., the ability to quickly search billions of table partitions for those relevant to a query). It also leverages this design to provide high-level features such as automatic data layout optimization, upserts, caching, and audit logs. Delta Lake tables can be accessed from Apache Spark, Hive, Presto, Redshift and other systems. Delta Lake is deployed at thousands of Databricks customers that process exabytes of data per day, with the largest instances managing exabyte-scale datasets and billions of objects.

Multi-pulse signals are composed of finite pulse streams of arbitrary pulse shape. With the pulse shape known, a multichannel sampling scheme for multi-pulse signals can operate at the rate of innovation, which is much lower than the Nyquist rate. The sampling system is based on low-pass filters, oscillators and integrators. By now there is no hardware to practice the approach. In this paper, we design a hardware system and discover that the non-idealities of low-pass filters will lead to failing in signal reconstruction. We research how the low-pass filters affect the reconstruction and solve the problem by channel calibration. The experiments show that channel calibration compensates most of the errors induced by low-pass filters, and this approach can achieve better estimation of time-delays and amplitudes of multi-pulse signals with a known pulse shape.

As data volumes continue to grow, modern database systems increasingly rely on data skipping mechanisms to improve performance by avoiding access to irrelevant data. Recent work [39] proposed a fine-grained partitioning scheme that was shown to improve the opportunities for data skipping in row-oriented systems. Modern analytics and big data systems increasingly adopt columnar storage schemes, and in such systems, a row-based approach misses important opportunities for further improving data skipping. The flexibility of column-oriented organizations, however, comes with the additional cost of tuple reconstruction. In this paper, we develop Generalized Skipping-Oriented Partitioning (GSOP), a novel hybrid data skipping framework that takes into account these row-based and column-based tradeoffs. In contrast to previous column-oriented physical design work, GSOP considers the tradeoffs between horizontal data skipping and vertical partitioning jointly. Our experiments using two public benchmarks and a real-world workload show that GSOP can significantly reduce the amount of data scanned and improve end-to-end query response times over the state-of-the- art techniques.

Modern query engines are increasingly being required to process enormous datasets in near real-time. While much can be done to speed up the data access, a promising technique is to reduce the need to access data through data skipping. By maintaining some metadata for each block of tuples, a query may skip a data block if the metadata indicates that the block does not contain relevant data. The effectiveness of data skipping, however, depends on how well the blocking scheme matches the query filters.

We propose to demonstrate a fine-grained partitioning framework that reorganizes the data tuples into small blocks at data loading time. The goal is to enable queries to maximally skip scanning data blocks. The partition framework consists of four steps: (1) workload analysis, which extracts features from a query workload, (2) augmentation, which augments each data tuple with a feature vector, (3) reduce, which succinctly represents a set of data tuples using a set of feature vectors, and (4) partitioning, which performs a clustering algorithm to partition the feature vectors and uses the clustering result to guide the actual data partitioning. Our experiments show that our techniques result in a 3-7x query response time improvement over traditional range partitioning due to more effective data skipping.

The Voronoi diagram is an important technique for answering nearest-neighbor queries for spatial databases. We study how the Voronoi diagram can be used for uncertain spatial data, which are inherent in scientific and business applications. Specifically, we propose the Uncertain-Voronoi diagram (or UV-diagram), which divides the data space into disjoint “UV-partitions”. Each UV-partition $$P$$ is associated with a set $$S$$ of objects, such that any point $$q$$ located in $$P$$ has the set $$S$$ as its nearest neighbor with nonzero probabilities. The UV-diagram enables queries that return objects with nonzero chances of being the nearest neighbor (NN) of a given point $$q$$ . It supports “continuous nearest-neighbor search”, which refreshes the set of NN objects of $$q$$ , as the position of $$q$$ changes. It also allows the analysis of nearest-neighbor information, for example, to find out the number of objects that are the nearest neighbors of any point in a given area. A UV-diagram requires exponential construction and storage costs. To tackle these problems, we devise an alternative representation of a UV-diagram, by using a set of UV-cells. A UV-cell of an object $$o$$ is the extent $$e$$ for which $$o$$ can be the nearest neighbor of any point $$q \in e$$ . We study how to speed up the derivation of UV-cells by considering its nearby objects. We also use the UV-cells to design the UV-index, which supports different queries, and can be constructed in polynomial time. We have performed extensive experiments on both real and synthetic data to validate the efficiency of our approaches.

The Voronoi diagram is an important technique for answering nearest-neighbor queries for spatial databases. In this paper, we study how the Voronoi diagram can be used on uncertain data, which are inherent in scientific and business applications. In particular, we propose the Uncertain-Voronoi Diagram (or UV-diagram in short). Conceptually, the data space is divided into distinct ¿UV-partitions¿, where each UV-partition P is associated with a set S of objects; any point q located in P has the set S as its nearest neighbor with non-zero probabilities. The UV-diagram facilitates queries that inquire objects for having non-zero chances of being the nearest neighbor of a given query point. It also allows analysis of nearest neighbor information, e.g., finding out how many objects are the nearest neighbors in a given area. However, a UV-diagram requires exponential construction and storage costs. To tackle these problems, we devise an alternative representation for UV-partitions, and develop an adaptive index for the UV-diagram. This index can be constructed in polynomial time. We examine how it can be extended to support other related queries. We also perform extensive experiments to validate the effectiveness of our approach.

Data uncertainty is inherent in applications such as sensor monitoring systems, location-based services, and biological databases. To manage this vast amount of imprecise information, probabilistic databases have been recently developed. In this paper, we study the discovery of frequent patterns and association rules from probabilistic data under the Possible World Semantics. This is technically challenging, since a probabilistic database can have an exponential number of possible worlds. We propose two effcient algorithms, which discover frequent patterns in bottom-up and top-down manners. Both algorithms can be easily extended to discover maximal frequent patterns. We also explain how to use these patterns to generate association rules. Extensive experiments, using real and synthetic datasets, were conducted to validate the performance of our methods.