This book constitutes revised selected papers from the workshops of the 4th Asia-Pacific Web and Web-Age Information Management International Joint Conference on Web and Big Data, APWeb-WAIM 2020: The Third International Workshop on Knowledge Graph Management and Applications, KGMA 2020; The Second International Workshop on Semi-structured Big Data Management and Applications, SemiBDMA 2020, and The First International Workshop on Deep Learning in Large-scale Unstructured Data Analytics, DeepLUDA 2020, held in Tianjin, China, in September 2020. Due to the COVID-19 pandemic the conference was held online. The 13 papers were thoroughly reviewed and selected from the numerous submissions and present recent research on the theory, design, and implementation of data management systems.