This book constitutes the proceedings of the 21st International Conference on Web Information Systems Engineering, WISE 2020, held in Amsterdam, The Netherlands, in October 2020.The 81 full papers presented were carefully reviewed and selected from 190 submissions.

Information Extraction.- TaskGenie: Crowd-powered Generation of Struggling Search Tasks.- Search Engine Similarity Analysis: A Combined Content and Rankings Approach.- Evaluating Similarity Measures for Dataset Search.- Towards Efficient Retrieval of Top-$k$ Entities in Systems of Engagement.- A Compare-Aggregate Model with External Knowledge for Query-focused Summarization.- An Active Learning Based Hybrid Neural Network for Joint Information Extraction.- ABLA: an algorithm for repairing structure-based locators through attribute annotations.- Text Mining.- Automatic action extraction for short text conversation using unsupervised learning.- Topic Analysis by Exploring Headline Information.- A Text Mining Approach to Extract and Rank Innovation Insights from Research Projects.- Automatic Complex Word Identification Using Implicit Feedback From User Copy Operations.- A Densely Connected Encoder Stack Approach for Multi-type Legal Machine Reading Comprehension.- Security and Privacy.- Privacy-Preserving Data Generation and Sharing Using Identification Sanitizer.- Robust Blockchain-based Cross-platform Audio Copyright Protection System Using Content-based Fingerprint.- Fragmentation in Outsourced Data Storage.- A Graph Data Privacy-Preserving Method based on Generative Adversarial Networks.- Channel Correlation Based Robust Audio Watermarking Mechanism For Stereo Signals.- Adaptive Online Learning for Vulnerability Exploitation Time Prediction.- Recommender Systems.- Double-Wing Mixture of Experts for Streaming Recommendations.- Modelling Local and Global Dependencies for Next-item Recommendations.- Why-Not Questions & Explanations for Collaborative Filtering.- Learning from Multiple Graphs of User and Book Interactions for Campus Book Recommendation.- A clustering-based collaborative filtering recommendation algorithm via deep learning user side information.- Path-Based Academic Paper Recommendation.- Database System and Workflow.- A Slice-Based Method to Speed Up Join View Maintenance for Transactions.- A Chunk-Based Hash Table Caching Method for In-Memory Hash Joins.- An Asynchronous View Maintenance Approach Based on IO Sharing.- AQapprox: Aggregation Queries Approximation with Distributionaware Online Sampling.- LogRank+: A Novel Approach to Support Business Process Event Log Sampling.- ProvONE+: A Provenance Model for Scientific Workflows.- Data Mining and Applications.- Fair Outlier Detection.- A new effective and efficient measure for outlying aspect mining.- Time Series Data Cleaning Based on Dynamic Speed Constraints.- Predicting MOOCs Dropout with A Deep Model.- RFRSF: Employee Turnover Prediction based on Random Forests and Survival Analysis.- A Deep Sequence-to-Sequence Method for Aircraft Landing Speed Prediction based on QAR Data.- Fine-grained Multi-label Sexism Classification using Semi-supervised Learning.- aDFR: An Attention-based Deep Learning Model for Flight Ranking.- Dealing With Ratio Metrics in A/B Testing at the Presence of Intra-User Correlation and Segments.- Risk Monitoring Services of Discharged SARS-CoV-2 Patients.- UAVFog-assisted Data-driven Disaster Response: Architecture, Use Case, and Challenges.