Machine Learning is the study of methods for programming computers to learn. Computers are applied to a wide range of tasks, and for most of these it is relatively easy for programmers to design and implement the necessary software. However, there are many tasks for which this is difficult or impossible. These can be divided into four general categories. First, there are problems for which there exist no human experts. For example, in modern automated manufacturing facilities, there is a need to predict machine failures before they occur by analyzing sensor readings. Because the machines are new, there are no human experts who can be interviewed by a programmer to provide the knowledge necessary to build a computer system. A machine learning system can study recorded data and subsequent machine failures and learn prediction rules. Second, there are problems where human experts exist, but where they are unable to explain their expertise. This is the case in many perceptual tasks, such as speech recognition, hand-writing recognition, and natural language understanding. Virtually all humans exhibit expert-level abilities on these tasks, but none of them can describe the detailed steps that they follow as they perform them. Fortunately, humans can provide machines with examples of the inputs and correct outputs for these tasks, so machine learning algorithms can learn to map the inputs to the outputs. Third, there are problems where phenomena are changing rapidly. In finance, for example, people would like to predict the future behavior of the stock market, of consumer purchases, or of exchange rates. These behaviors change frequently, so that even if a programmer could construct a good predictive computer program, it would need to be rewritten frequently. A learning program can relieve the programmer of this burden by constantly modifying and tuning a set of learned prediction rules. Fourth, there are applications that need to be customized for each computer user separately. Consider, for example, a program to filter unwanted electronic mail messages. Different users will need different filters. It is unreasonable to expect each user to program his or her own rules, and it is infeasible to provide every user with a software engineer to keep the rules up-to-date. A machine learning system can learn which mail messages the user rejects and maintain the filtering rules automatically. Machine learning addresses many of the same research questions as the fields of statistics, data mining, and psychology, but with differences of emphasis. Statistics focuses on understanding the phenomena that have generated the data, often with the goal of testing different hypotheses about those phenomena. Data mining seeks to find patterns in the data that are understandable by people. Psychological studies of human learning aspire to understand the mechanisms underlying the various learning behaviors exhibited by people (concept learning, skill acquisition, strategy change, etc.).

Machine learning

Data Mining - Concepts and Techniques.

Social Network Analysis

We study the problem of representation learning in heterogeneous networks. Its unique challenges come from the existence of multiple types of nodes and links, which limit the feasibility of the conventional network embedding techniques. We develop two scalable representation learning models, namely metapath2vec and metapath2vec++. The metapath2vec model formalizes meta-path-based random walks to construct the heterogeneous neighborhood of a node and then leverages a heterogeneous skip-gram model to perform node embeddings. The metapath2vec++ model further enables the simultaneous modeling of structural and semantic correlations in heterogeneous networks. Extensive experiments show that metapath2vec and metapath2vec++ are able to not only outperform state-of-the-art embedding models in various heterogeneous network mining tasks, such as node classification, clustering, and similarity search, but also discern the structural and semantic correlations between diverse network objects.

https://dl.acm.org/doi/pdf/10.1145/3097983.3098036

metapath2vec: Scalable Representation Learning for Heterogeneous Networks

The Analysis of Time Series: An Introduction, 4th edn. By C. Chatfield. ISBN 0 412 31820 2. Chapman and Hall, London, 1989. 242 pp. £13.50.

The Analysis of Time Series: An Introduction

Large graphs are prevalent in social networks, traffic networks, and biology. These graphs are often inexact. For example, in a friendship network, an edge between two nodesu andv indicates that users u and v have a close relationship. This edge may only exist with a probability. To model such information, the uncertain graph model has been proposed, in which each edge e is augmented with a probability that indicate the chance that e exists. Given a node q in an uncertain graph G, we study the k-NN query of q, which looks for k nodes in G whose distances from q are the shortest. The k-NN query can be used in friend-search, data mining, and pattern-recognition. Despite the importance of this query, it has not been well studied. In this paper, we develop a tree-based structure called the U-tree. Given a k-NN query, the U-tree produces a compact representation of G, based on which the query can be executed efficiently. Our results on real and synthetic datasets show that our algorithm can scale to large graphs, and is 75% faster than the state-of-the-art solutions.

Scalable Evaluation of k-NN Queries on Large Uncertain Graphs.

Pervasive applications, such as natural habitat monitoring and location-based services, have attracted plenty of research interest These applications deploy a large number of sensors (eg temperature sensors) and positioning devices (eg GPS) to collect data from external environments Very often, these systems have limited network bandwidth and battery resources The sensors also cannot record accurate values The uncertainty of these data hence has to been taken into account for query evaluation purposes In particular, probabilistic queries, which consider data impreciseness and provide statistical guarantees in answers, have been recently studied In this paper, we investigate how to evaluate a long-standing (or continuous) probabilistic query We propose the probabilistic filter protocol, which governs remote sensor devices to decide upon whether values collected should be reported to the query server This protocol effectively reduces the communication and energy costs of sensor devices We also introduce the concept of probabilistic tolerance, which allows a query user to relax answer accuracy, in order to further reduce the utilization of resources Extensive simulations on realistic data show that our method reduces by address more than 99% of savings in communication costs

Evaluating continuous probabilistic queries over imprecise sensor data

In crowdsourcing, human workers are employed to tackle problems that are traditionally difficult for computers (e.g., data cleaning, missing value filling, and sentiment analysis). In this paper, we study the effective use of crowdsourcing in filling missing values in a given relation (e.g., a table containing different attributes of celebrity stars, such as nationality and age). A task given to a worker typically consists of questions about the missing attribute values (e.g., What is the age of Jet Li?). Although this problem has been studied before, existing work often treats related attributes independently, leading to suboptimal performance. In this paper, we present T-Crowd, which is a crowdsourcing system that considers attribute relationships. Particularly, T-Crowd integrates each worker's answers on different attributes to effectively learn his/her trustworthiness and the true data values. The attribute relationship information is used to guide task allocation to workers. Our solution seamlessly supports categorical and continuous attributes. Our extensive experiments on real and synthetic datasets show that T-Crowd outperforms state-of-the-art methods, improving the quality of truth inference and reducing the monetary cost of crowdsourcing.

A Crowdsourcing Framework for Collecting Tabular Data

A distributed database utilizing the wide-spread edge computing servers to provide low-latency data access with the serializability guarantee is highly desirable for emerging edge computing applications. In an edge database, nodes are divided into regions, and a transaction can be categorized as intra-region (IRT) or cross-region (CRT) based on whether it accesses data in different regions. In addition to serializability, we insist that a practical edge database should provide low tail latency for both IRTs and CRTs, and such low latency must be scalable to a large number of regions. Unfortunately, none of existing geo-replicated serializable databases or edge databases can meet such requirements. In this paper, we present Dast (Decentralized Anticipate and STretch), the first edge database that can meet the stringent performance requirements with serializability. Our key idea is to order transactions by anticipating when they are ready to execute: Dast binds an IRT to the latest timestamp and binds a CRT to a future timestamp to avoid the coordination of CRTs blocking IRTs. Dast also carries a new stretchable clock abstraction to tolerate inaccurate anticipations and to handle cross-region data reads. Our evaluation shows that, compared to three relevant serializable databases, Dast's 99-percentile latency was 87.9%~93.2% lower for IRTs and 27.7%~70.4% lower for CRTs; Dast's low latency is scalable to a large number of regions.

https://dl.acm.org/doi/pdf/10.1145/3447786.3456238

Achieving low tail-latency and high scalability for serializable transactions in edge computing

Given a directed graph G, the directed densest subgraph (DDS) problem refers to finding a subgraph from G, whose density is the highest among all subgraphs of G. The DDS problem is fundamental to a wide range of applications, such as fake follower detection and community mining. Theoretically, the DDS problem closely connects to other essential graph problems, such as network flow and bipartite matching. However, existing DDS solutions suffer from efficiency and scalability issues. In this paper, we develop a convex-programming-based solution by transforming the DDS problem into a set of linear programs. Based on the duality of linear programs, we develop efficient exact and approximation algorithms. Especially, our approximation algorithm can support flexible parameterized approximation guarantees. We have performed an extensive empirical evaluation of our approaches on eight real large datasets. The results show that our proposed algorithms are up to five orders of magnitude faster than the state-of-the-art.

Reynold Cheng

Papers

Scalable Evaluation of k-NN Queries on Large Uncertain Graphs.

Evaluating continuous probabilistic queries over imprecise sensor data

A Crowdsourcing Framework for Collecting Tabular Data

Achieving low tail-latency and high scalability for serializable transactions in edge computing

A Convex-Programming Approach for Efficient Directed Densest Subgraph Discovery