​This book constitutes revised selected papers from the workshops of the 5th Asia-Pacific Web and Web-Age Information Management International Joint Conference on Web and Big Data, APWeb-WAIM 2021: The Fourth International Workshop on Knowledge Graph Management and Applications, KGMA 2021, The Third International Workshop on Semi-structured Big Data Management and Application, SemiBDMA 2021, and The Second International Workshop on Deep Learning in Large-scale Unstructured Data Analytics, DeepLUDA 2021, held in Guangzhou, China, in August 2021. Due to the COVID-19 pandemic the conference was held online. The 11 papers were thoroughly reviewed and selected from the 28 submissions and present recent research on the theory, design, and implementation of data management systems.