This book constitutes the proceedings of the 20th International Semantic Web Conference, ISWC 2021, which took place in October 2021. Due to COVID-19 pandemic the conference was held virtually. The papers included in this volume deal with the latest advances in fundamental research, innovative technology, and applications of the Semantic Web, linked data, knowledge graphs, and knowledge processing on the Web. Papers are organized in a research track, resources and in-use track. The research track details theoretical, analytical and empirical aspects of the Semantic Web and its intersection with other disciplines. The resources track promotes the sharing of resources which support, enable or utilize semantic web research, including datasets, ontologies, software, and benchmarks. And finally, the in-use-track is dedicated to novel and significant research contributions addressing theoretical, analytical and empirical aspects of the Semantic Web and its intersection with other disciplines.

Welcome to the proceedings of the 4th European Conference on Smart Se- ing and Context hosted by the Centre for Communication Systems Research, University of Surrey, in Guildford, UK. Smart sensing and context are the key enablers for e?ective autonomous systems, providing transparent technologies to realize the vision of ubiquitous computing, intelligent services and networking. (Wireless) Sensor and actuator networks,tightly integratedinto the structure of the Internet provide the und- lying manifestation of the physical world into the Internet of Things. Networked sensorscaninfercontextfromrawdataandcaptureuserandapplicationneedsto provide smart adaptive services. Higher-level context can be deducted locally or remotelybycombining andabstractinginformationfromsmartsensors. The 4th European Conference on Smart Sensing and Context explored new techniques, algorithmsandarchitectures onutilizing contextandcontext-awareservicesand their applications. The conference builds on the success of the past editions held in Zu ..rich, Switzerland in 2008, in Kendal, UK in 2007 and in Enschede, The Netherlands in 2006. EuroSSC is a forum to exchange ideas and to discuss the most recent developments in smart sensing and context ?eld. It explores the latest ?ndings and state-of-the-art developments in technology, covering human and user aspects. The main topics discussed this year focused on embedded - plications, context-aware platforms, context processing, semantic technologies, mobile platforms and real-worlddeployment and exploitation scenarios. The - velopment of integrating sensor and actuator networks and context-platforms in a wider scale setting has added a new dimension to global networks and has - abled users and applications to interact with the physical world more e?ciently.