​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.