This book constitutes the refereed proceedings of the 21st International Conference on Big Data Analytics and Knowledge Discovery, DaWaK 2019, held in Linz, Austria, in September 2019.

Applications.- Detecting the Onset of Machine Failure Using Anomaly Detection Methods.- A Hybrid Architecture for Tactical and Strategic Precision Agriculture.- Urban analytics of big transportation data for supporting smart cities.- Patterns.- Frequent Item Mining When Obtaining Support is Costly.- Mining Sequential Pattern of Historical Purchases for E-Commerce Recommendation.- Discovering and Visualizing Efficient Patterns in Cost/Utility Sequences.- Efficient Row Pattern Matching using Pattern Hierarchies for Sequence OLAP.- Statistically Significant Discriminative Patterns Searching.- RDF and Streams.- Multidimensional Integration of RDF datasets.- RDFPartSuite: Bridging Physical and Logical RDF Partitioning.- Mining quantitative temporal dependencies between interval-based streams.- Democratization of OLAP DSMS.- Big Data Systems.- Leveraging the Data Lake - Current State and Challenges.- SDWP: A New Data Placement Strategy for Distributed Big DataWarehouses in Hadoop.- Improved Programming-Language Independent MapReduce on Shared-Memory Systems.- Evaluating Redundancy and Partitioning of Geospatial Data in Document-Oriented Data Warehouses.- Graphs and Machine Learning.- Scalable Least Square Twin Support Vector Machine Learning.- Finding Strongly Correlated Trends in Dynamic Attributed Graphs.- Text-based Event Detection: Deciphering Date Information Using Graph Embeddings.- Efficiently Computing Homomorphic Matches of Hybrid Pattern Queries on Large Graphs.- Databases.- From Conceptual to Logical ETL Design using BPMN and Relational Algebra.- Accurate Aggregation Query-Result Estimation and Its Efficient Processing on Distributed Key-Value Store.