Invited Papers -- Mining Incomplete Data Using Global and Saturated Probabilistic Approximations Based on Characteristic Sets and Maximal Consistent Blocks -- Determining Tanimoto Similarity Neighborhoods of Real-Valued Vectors by Means of the Triangle Inequality and Bounds on Length -- Rough-Fuzzy Segmentation of Brain MR Volumes: Applications in Tumor Detection and Malignancy Assessment -- DDAE-GAN: Seismic Data Denoising by Integrating Autoencoder and Generative Adversarial Network -- Classification of Multi-Class Imbalanced Data: Data Difficulty Factors and Selected Methods for Improving Classifiers -- Core Rough Set Models and Methods -- General Rough Modeling of Cluster Analysis -- Possible Coverings in Incomplete Information Tables with Similarity of Values -- Attribute Reduction Using Functional Dependency Relations in Rough Set Theory -- The RSDS: A Current State and Future Plans -- Many-Valued Dynamic Object-Oriented Inheritance and Approximations -- Related Methods and Hybridization -- Minimizing Depth of Decision Trees with Hypotheses -- The Influence of Fuzzy Expectations on Triples of Triangular Norms in the Weighted Fuzzy Petri Net for the Subject Area of Passenger Transport Logistics -- Possibility Distributions Generated by Intuitionistic L-Fuzzy Sets -- Feature Selection and Disambiguation in Learning from Fuzzy Labels using Rough Sets -- Right Adjoint Algebras versus Operator Left Residuated posets -- Adapting Fuzzy Rough Sets for Classification with Missing Values -- Areas of Applications -- Spark Accelerated Implementation of Parallel Attribute Reduction from Incomplete Data -- Attention Enhanced Hierarchical Feature Representation for Three-way Decision Boundary Processing -- An Opinion Summarization-Evaluation System Based on Pre-trained Models -- Fuzzy-Rough Nearest Neighbour Approaches for Emotion Detection in Tweets -- Three-way decisions based RNN models for sentiment classification -- Tolerance-Based Short Text Sentiment Classifier -- Knowledge Graph Representation Learning for Link Prediction with Three-Way Decisions -- PNeS in Modelling, Control and Analysis of Concurrent Systems -- 3RD: A Multi-Criteria Decision-Making Method Based on Three-Way Rankings.

The volume LNAI 12872 constitutes the proceedings of the International Joint Conference on Rough Sets, IJCRS 2021, Bratislava, Slovak Republic, in September 2021. The conference was held as a hybrid event due to the COVID-19 pandemic. The 13 full paper and 7 short papers presented were carefully reviewed and selected from 26 submissions, along with 5 invited papers. The papers are grouped in the following topical sections: core rough set models and methods, related methods and hybridization, and areas of applications.