Message from the Workshop Chairs Ludovico Iovino 0 Lars Michael Kristensen 1 Gran Sasso Science Institute , L'Aquila , Italy Western Norway University of Applied Sciences, Faculty of Engineering and Science , Bergen , Norway

This volume contains the technical papers presented at three workshops collocated with the 2021 edition of the Software Technologies: Applications and Foundations (STAF) federation of conferences on software technologies. The STAF conferences, satellite events and workshops bring together leading researchers and practitioners from academia and industry to advance the state of the art in practical and foundational advances in software technology. They address all aspects of software technology, from object-oriented design, testing, mathematical approaches to modeling and verification, transformation, model-driven engineering, aspect-oriented techniques, and tools. As a consequence of the COVID-19 pandemic, STAF 2021 was organised as a virtual event organised by the Western Norway University of Applied Sciences (Bergen, Norway) from June 21 to June 25, 2021. STAF 2021 included the following workshops: • 9th International Workshop on Bidirectional Transformations (Bx 2021). Organisers: Leen Lambers, and Meng Wang. • Joint Workshop on Foundations and Practice of Visual Modeling (FPVM) and Data for Model-Driven Engineering (Data4MDE). Organisers: Amleto Di Salle, Alfonso Pierantonio, Juha-Pekka Tolvanen, Juri Di Rocco, Juan De Lara, and Michel Chaudron • International workshop on MDE for Smart IoT Systems (MeSS'21). Organisers: Ludovico Iovino, Manuel Wimmer, Federico Ciccozzi, Sébastien Mosser, Nicolas Ferry, Arnor Solberg • 4th International Workshop on (Meta)Modeling for Healthcare Systems (MMHS 2021). Organisers: Ludovico Iovino, Adrian Rutle, Yngve Lamo, and Wendy MacCaul • 20th International Workshop on OCL and Textual Modeling (OCL'2021). Organisers: Daniel Calegari, Robert Clarisó, and Edward D. Willink We would like to thank the workshop organizers; whose hard work, despite the dificulties and challenges, made their events successful. Thanks to the local organizers of STAF 2021 for their trust and support. Finally, we would also like to thank all the participants and people who have contributed to the events as well as the respective Program Committee members and external reviewers who carried out thorough and careful reviews. September 2021, Ludovico Iovino and Lars Michael Kristensen