This two volume set of LNCS 11706 and LNCS 11707 constitutes the refereed proceedings of the 30th International Conference on Database and Expert Systems Applications, DEXA 2019, held in Linz, Austria, in August 2019.The 32 full papers presented together with 34 short papers were carefully reviewed and selected from 157 submissions.

Distributed, Parallel, P2P, Grid and Cloud databases.- Looking into the Peak Memory Consumption of Epoch-based Reclamation in Scalable In-Memory Database Systems.- Energy Efficient Data Placement and Buffer Management for Multiple Replication.- Querying Knowledge Graphs with Natural Languages.- Explaining Query Answer Completeness and Correctness With Partition Patterns.- Information Retrieval.- Research Paper Search Using a Topic-based Boolean Query Search and a General Query-based Ranking Model.- Extractive Document Summarization using Non-negative Matrix Factorization.- Succinct BWT-based Sequence prediction.- TRR: Reducing Crowdsourcing Task Redundancy.- Software Resource Recommendation for Process Execution based on the Organization's Profile.- An Experiment to Analyze the Use of Process Modeling Guidelines to Create High-Quality Process Models.- Semantic Web and Ontologies.- Novel Node Importance Measures to Improve Keyword Search over RDF Graphs.- Querying in a Workload-aware Triplestore based on NoSQL Databases.- Reverse Partitioning for SPARQL Queries: Principles and Performance Analysis.- PFed: Recommending Plausible Federated SPARQL Queries.- Representing and Reasoning about Precise and Imprecise Time Points and Intervals in Semantic Web: Dealing with Dates and Time Clocks.- Information Processing.- Context-Aware Multi-Criteria Recommendation Based on Spectral Graph Partitioning.- SilverChunk: An Efficient In-Memory Parallel Graph Processing System.- A modular approach for efficient simple question answering over knowledge base.- Scalable Machine Learning in the R Language Using a Summarization Matrix.- ML-PipeDebugger: A Debugging Tool for Data Processing Pipelines.- Temporal, Spatial, and High Dimensional Databases.- Correlation Set Discovery on Time-series Data.- Anomaly Subsequence Detection with Dynamic Local Density for Time Series.- Trajectory Similarity Join for Spatial Temporal Database.- Knowledge Discovery.- Multiviewpoint-based Agglomerative Hierarchical Clustering.- Triplet-CSSVM: Integrating Triplet-Sampling CNN and Cost-Sensitive Classification for Imbalanced Image Detection.- Discovering Partial Periodic High Utility Itemsets in Temporal Databases.- Using Mandatory Concepts for Knowledge Discovery and Data Structuring.- Topological Data Analysis with \epsilon-net Induced Lazy Witness Complex.- Analyzing Sequence Pattern Variants in Sequential Pattern Mining and its Application to Electronic Medical Record Systems.- Web Services.- Composing Distributed Data-intensive Web services using Distance-guided Memetic Algorithm.- Keyword Search based Mashup Construction with Guaranteed Diversity.- Using EDA-Based Local Search to improve the performance of NSGA-II for Multiobjective Semantic Web Service Composition.- Adaptive Caching for Data-Intensive Scientific Workflows in the Cloud.