Keyword-based Search over Databases: A Roadmap for a Reference Architecture Paired with an Evaluation Framework -- Entity-based Keyword Search in Web Documents -- Evaluation of Keyword Search in Affective Multimedia Databases -- Subject-related Message Filtering in Social Media Through Context-enriched Language Models -- Improving Open Information Extraction for Semantic Web Tasks -- Searching Web 2.0 Data through Entity-Based Aggregation.

These transactions publish research in computer-based methods of computational collective intelligence (CCI) and their applications in a wide range of fields such as the semantic Web, social networks, and multi-agent systems. TCCI strives to cover new methodological, theoretical and practical aspects of CCI understood as the form of intelligence that emerges from the collaboration and competition of many individuals (artificial and/or natural). The application of multiple computational intelligence technologies, such as fuzzy systems, evolutionary computation, neural systems, consensus theory, etc., aims to support human and other collective intelligence and to create new forms of CCI in natural and/or artificial systems. This twenty-first issue contains 7 carefully selected and revised contributions.