Metaverse describes a new shape of cyberspace and has become a hot-trending word since 2021. There are many explanations about what Meterverse is and attempts to provide a formal standard or definition of Metaverse. However, these definitions could hardly reach universal acceptance. Rather than providing a formal definition of the Metaverse, we list four must-have characteristics of the Metaverse: socialization, immersive interaction, real world-building, and expandability. These characteristics not only carve the Metaverse into a novel and fantastic digital world, but also make it suffer from all security/privacy risks, such as personal information leakage, eavesdropping, unauthorized access, phishing, data injection, broken authentication, insecure design, and more. This paper first introduces the four characteristics, then the current progress and typical applications of the Metaverse are surveyed and categorized into four economic sectors. Based on the four characteristics and the findings of the current progress, the security and privacy issues in the Metaverse are investigated. We then identify and discuss more potential critical security and privacy issues that can be caused by combining the four characteristics. Lastly, the paper also raises some other concerns regarding society and humanity. 

/pdf/security-and-privacy-in-metaverse-a-comprehensive-survey-26695nbz.pdf

Security and Privacy in Metaverse: A Comprehensive Survey

Many important data management and analytics tasks cannot be completely addressed by automated processes. Crowdsourcing is an effective way to harness human cognitive abilities to process these computer-hard tasks, such as entity resolution, sentiment analysis, and image recognition. Crowdsourced data management has been extensively studied in research and industry recently. In this tutorial, we will survey and synthesize a wide spectrum of existing studies on crowdsourced data management. We first give an overview of crowdsourcing, and then summarize the fundamental techniques, including quality control, cost control, and latency control, which must be considered in crowdsourced data management. Next we review crowdsourced operators, including selection, collection, join, top-k, sort, categorize, aggregation, skyline, planning, schema matching, mining and spatial crowdsourcing. We also discuss crowdsourcing optimization techniques and systems. Finally, we provide the emerging challenges.

Crowdsourced Data Management: Overview and Challenges

Crowdsourcing has been shown to be effective in a wide range of applications, and is seeing increasing use. A large-scale crowdsourcing task often consists of thousands or millions of atomic tasks, each of which is usually a simple task such as binary choice or simple voting. To distribute a large-scale crowdsourcing task to limited crowd workers, a common practice is to pack a set of atomic tasks into a task bin and send to a crowd worker in a batch. It is challenging to decompose a large-scale crowdsourcing task and execute batches of atomic tasks, which ensures reliable answers at a minimal total cost. Large batches lead to unreliable answers of atomic tasks, while small batches incur unnecessary cost. In this paper, we investigate a general crowdsourcing task decomposition problem, called the S mart L arge-sc A le task DE composer (SLADE) problem, which aims to decompose a large-scale crowdsourcing task to achieve the desired reliability at a minimal cost. We prove the NP-hardness of the SLADE problem and propose solutions in both homogeneous and heterogeneous scenarios. For the homogeneous SLADE problem, where all the atomic tasks share the same reliability requirement, we propose a greedy heuristic algorithm and an efficient and effective approximation framework using an optimal priority queue (OPQ) structure with provable approximation ratio. For the heterogeneous SLADE problem, where the atomic tasks can have different reliability requirements, we extend the OPQ-based framework leveraging a partition strategy, and also prove its approximation guarantee. Finally, we verify the effectiveness and efficiency of the proposed solutions through extensive experiments on representative crowdsourcing platforms.

https://ink.library.smu.edu.sg/cgi/viewcontent.cgi?article=5537&context=sis_research

SLADE: A Smart Large-Scale Task Decomposer in Crowdsourcing

With the rapid development of smartphones, spatial crowdsourcing platforms are getting popular. A foundational research of spatial crowdsourcing is to allocate micro-tasks to suitable crowd workers. Many existing studies focus on the offline scenario, where all the spatiotemporal information of micro-tasks and crowd workers is given. In this paper, we focus on the online scenario and identify a more practical micro-task allocation problem, called the G lobal O nline M icro-task A llocation in spatial crowdsourcing (GOMA) problem. We first extend the state-of-the-art algorithm for the online maximum weighted bipartite matching problem to the GOMA problem as the baseline algorithm. Although the baseline algorithm provides a theoretical guarantee for the worst case, its average performance in practice is not good enough since the worst case happens with a very low probability in the real world. Thus, we consider the average performance of online algorithms, a.k.a. random order model. We propose a two-phase-based framework, based on which we present the TGOA algorithm with a $\frac{1}{4}$ 1 4 -competitive ratio under the random order model. To improve its efficiency, we further design the TGOA-Greedy and TGOA-OP algorithm following this framework, which runs faster than the TGOA algorithm with a competitive ratio of $\frac{1}{8}$ 1 8 and $\frac{1}{4}$ 1 4 , respectively. We also revisit the average performance of Greedy, which has long been considered as the worst due to its unbounded competitive ratio in the worst case. Finally, we verify the effectiveness and efficiency of the proposed methods through extensive experiments on synthetic and real datasets.

Two-Sided Online Micro-Task Assignment in Spatial Crowdsourcing

In this paper, we study a new type of spatial crowdsourcing, namely competitive detour tasking, where workers can make detours from their original travel paths to perform multiple tasks, and each worker is allowed to compete for preferred tasks by strategically claiming his/her detour costs. The objective is to make suitable task assignment by maximizing the social welfare of crowdsourcing systems and protecting workers’ private sensitive information. We first model the task assignment problem as a reverse auction process. We formalize the winning bid selection of reverse auction as an $n$ n -to-one weighted bipartite graph matching problem with multiple 0-1 knapsack constraints. Since this problem is NP-hard, we design an approximation algorithm to select winning bids and determine corresponding payments. Based on this, a Secure Reverse Auction (SRA) protocol is proposed for this novel spatial crowdsourcing. We analyze the approximation performance of the proposed protocol and prove that it has some desired properties, including truthfulness, individual rationality, computational efficiency, and security. To the best of our knowledge, this is the first theoretically provable secure auction protocol for spatial crowdsourcing systems. In addition, we also conduct extensive simulations on a real trace to verify the performance of the proposed protocol.

SRA: Secure Reverse Auction for Task Assignment in Spatial Crowdsourcing

Crowd-powered database systems can leverage the crowd's ability to address machine-hard problems, eg, data integration Existing crowdsourcing systems adopt the traditional tree model to select a good query plan However, the tree model can optimize the I/O cost but cannot optimize the monetary cost, latency and quality, which are three important optimization goals in crowdsourcing To address this limitation, we demonstrate CDB, a crowd-powered database system CDB proposes a new graph-based model that adopts a fine-grained tuple-level optimization model which significantly outperforms existing coarse-grained tree-based optimization models Moreover, CDB provides a unified framework to simultaneously optimize the monetary cost, quality and latency We have deployed CDB on well-known crowd-sourcing platforms and users can easily use our system to deploy their applications We will demonstrate how to use CDB to address real-world applications, including web table integration and entity collection

/pdf/cdb-a-crowd-powered-database-system-4j14l5ceqm.pdf

CDB: a crowd-powered database system

Crowdsourced selection asks the crowd to select entities that satisfy a query condition, e.g., selecting the photos of people wearing sunglasses from a given set of photos. Existing studies focus on a single query predicate and in this paper we study the crowdsourced selection problem on multi-attribute data, e.g., selecting the female photos with dark eyes and wearing sunglasses. A straightforward method asks the crowd to answer every entity by checking every predicate in the query. Obviously, this method involves huge monetary cost. Instead, we can select an optimized predicate order and ask the crowd to answer the entities following the order. Since if an entity does not satisfy a predicate, we can prune this entity without needing to ask other predicates and thus this method can reduce the cost. There are two challenges in finding the optimized predicate order. The first is how to detect the predicate order and the second is to capture correlation among different predicates. To address this problem, we propose predicate order based framework to reduce monetary cost. Firstly, we define an expectation tree to store selectivities on predicates and estimate the best predicate order. In each iteration, we estimate the best predicate order from the expectation tree, and then choose a predicate as a question to ask the crowd. After getting the result of the current predicate, we choose next predicate to ask until we get the result. We will update the expectation tree using the answer obtained from the crowd and continue to the next iteration. We also study the problem of answering multiple queries simultaneously, and reduce its cost using the correlation between queries. Finally, we propose a confidence based method to improve the quality. The experiment result shows that our predicate order based algorithm is effective and can reduce cost significantly compared with baseline approaches.

Crowdsourced Selection on Multi-Attribute Data

In this paper, we consider the crowdsourced select query with multiple predicates We find that different predicates have different selectivities An important problem is to determine a good predicate order However it is rather hard to obtain an optimal order To address this problem, we propose a sampling-based framework to find a high-quality order We devise a minimum random selection method by randomly selecting the predicate sequence Since minimum random selection randomly selects predicate permutations over predicates, which may bring large cost, we propose a filtering based algorithm to further reduce the cost We evaluate our method using a real-world dataset Experimental results indicate that our methods significantly reduce the monetary cost

A Sampling-Based Framework for Crowdsourced Select Query with Multiple Predicates

Crowdsourcing database systems have been proposed to leverage crowd-powered operations to encapsulate the complexities of interacting with the crowd. Existing systems suffer from two major limitations. Firstly, in order to optimize a query, they often adopt the traditional tree model to select an optimized table-level join order. However, the tree model provides a coarse-grained optimization, which generates the same order for different joined tuples and limits the optimization potential that different joined tuples can be optimized by different orders. Secondly, they mainly focus on optimizing the monetary cost. In fact, there are three optimization goals (i.e., smaller monetary cost, lower latency, and higher quality) in crowdsourcing, and it calls for a system to enable multi-goal optimization. To address the limitations, we develop a crowd-powered database system CDB that supports crowd-based query optimizations, with focus on join and selection. CDB has fundamental differences from existing systems. First, CDB employs a graph-based query model that provides more fine-grained query optimization. Second, CDB adopts a unified framework to perform the multi-goal optimization based on the graph model. We have implemented our system and deployed it on AMT, CrowdFlower and ChinaCrowd. We have also created a benchmark for evaluating crowd-powered databases. We have conducted both simulated and real experiments, and the experimental results demonstrate the performance superiority of CDB on cost, latency and quality.

CDB: Optimizing Queries with Crowd-Based Selections and Joins

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CDB: a crowd-powered database system

Crowdsourced Selection on Multi-Attribute Data

A Sampling-Based Framework for Crowdsourced Select Query with Multiple Predicates

CDB: Optimizing Queries with Crowd-Based Selections and Joins