- Claudia d'Amato (University of Bari 0 - Ernesto Jimenez-Ruiz (City University of London, UK) on Ontology Alignment and the Two DLs, - Nicole Schweikardt (Humboldt University of Berlin, Germany) on Locality Properties of Extensions of First-Order Logic and their Use in Algorithms, and - Luciano Serafini (FBK Trento, Italy) on Learning and Reasoning with Logic Tensor Networks: The Framework and an Application

s. DL 2021 offered an interesting and diverse program, which in addition to the technical papers, included four invited talks by leading experts: The invited talk by Luciano Serafini was joint with the Workshop on Data Meets Applied Ontologies in XAI (DAO-XAI 2021). This year's Best Student Contribution Award was presented to Quentin Manière for the paper “Counting Queries over E LHI? Ontologies. It is a tradition at the DL workshop to give a prize for the best contribution that was primarily produced by a student or students. Seven nominations of papers with students as co-authors were received from more senior co-authors of these papers. The Program Committee (without members who had conflict of interest) voted to give the award to this paper.

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We are indebted to the Program Committee and the additional reviewers for their invaluable efforts in providing helpful and informative reviews for all submissions in a timely fashion, in spite of the unique challenges this year. For advice and support we thank members of the DL Steering Committee. The organization and reviewing process was simplified a lot by the EasyChair conference management system and we thank CEUR for publishing these proceedings. The workshop would not be possible without the submissions and participation of all the people that make DL such a great community.

We are very grateful to the Foundation for Principles of Knowledge Representation and Reasoning (KR Inc.), the Artificial Intelligence Journal, and the European Association for Artificial Intelligence for committing generous funds for students and invited speakers in the face of considerable uncertainties. We further acknowledge additional support from the Slovak Research and Development Agency under the project ORBIS, contract No APVV-19-0220.

Finally, special thanks must go to Ján Kľuka and Júlia Pukancová for their engagement in the local organization and to the students who helped as volunteers.

 September 2021 Martin Homola (General Chair & Local Organizer) Vladislav Ryzhikov (Program Committee Co-Chair) Renate Schmidt (Program Committee Co-Chair) Program Committee Chairs Vladislav Ryzhikov Renate Schmidt Birkbeck, University of London, UK The University of Manchester, UK General Chair and Local Organizer Martin Homola Sponsorship Chair Jean Christoph Jung Publicity Chairs

Ján Kľuka Júlia Pukancová

 Program Committee Alessandro Artale

Franz Baader Meghyn Bienvenu Alex Borgida Stefan Borgwardt Arina Britz Diego Calvanese

 David Carral

Ismail Ilkan Ceylan Jieying Chen Roberto Confalonieri Bernardo Cuenca Grau Cristina Feier Laura Giordano Birte Glimm Victor Gutierrez-Basulto Martin Homola Yazmin A. Ibanez-Garcia Jean Christoph Jung Comenius University in Bratislava, Slovakia Stiftung Universität Hildesheim and Universität Bremen, Germany Comenius University in Bratislava, Slovakia Comenius University in Bratislava, Slovakia

Steering Committee Stefan Borgwardt Jean Christoph Jung Boris Konev

Ana Ozaki Thomas Schneider Mantas Simkus Martin Homola Vladislav Ryzhikov Renate Schmidt

 TU Dresden,Germany

Stiftung Universität Hildesheim and Universität Bremen, Germany University of Liverpool, UK University of Bergen, Norway Universität Bremen, Germany Vienna University of Technology, Austria Comenius University in Bratislava, Slovakia Birkbeck, University of London, UK The University of Manchester, UK