Hybrid human-machine query processing systems, such as crowd-powered database systems, aim to broaden the scope of questions users can ask about their data by incorporating human computation to support queries that may be subjective and/or require visual or semantic interpretation. A common type of query involves filtering data by several criteria, some of which need human computation to be evaluated. For example, filtering a set of hotels for those that both (1) have great views from the rooms, and (2) have a fitness center. Criteria can differ in the amount of human effort required to decide if data satisfy them, due to criterion's subjectivity and difficulty. There is potential to reduce crowdsourcing costs by ordering the evaluation of each of the criteria such that criteria needing more human computation are not processed for data that have not satisfied the less costly criteria. Unfortunately, for queries specified on-the-fly, the information about subjectivity and difficulty is unknown a priori. To overcome this challenge, we present Dynamic Filter, an adaptive query processing algorithm that dynamically changes the order in which criteria are evaluated based on observations while the query is running. Using crowdsourced data from a popular crowdsourcing platform, we show that Dynamic Filter can effectively adapt the processing order and approach the performance of a "clairvoyant" algorithm.
Published Date: 2017-10-27
Registration: ISBN 978-1-57735-793-3