Twitris, a Semantic Web application that facilitates understanding of social perceptions by Semantics-based processing of massive amounts of event-centric data. Twitris addresses challenges in large scale processing of social data, preserving spatio-temporal-thematic properties and focusing on multi-dimensional analysis of sptatio-temporal-thematic, people-content-network and sentiment-emotion-subjectivity facets. Twitris also covers context based semantic integration of multiple Web resources and expose semantically enriched social data to the public domain. Semantic Web technologies enable the system's integration and analysis abilities. It has applications for studying and analyzing social sensing and perception of a broad variety of events: politics and elections, social movements and uprisings, crisis and disasters, entertainment, environment, decision making and coordination, brand management, campaign effectiveness, etc.