The decentralization of the energy system coupled with advancements on IoT, big data, AI and distributed computing are creating a new momentum for exploiting data-driven services to improve buildings energy efficiency. Despite a large number of buildings data hubs and vocabularies have become available, some barriers hamper the exploitation of that potential, such as the lack of interoperability among heterogeneous static (e.g.BIM), building automation and IoT dynamic data sources and ontologies, and the lack of interoperable big data architectures fully tailored to smart buildings. In that respect MATRYCS will i) deliver an open Reference Architecture for Smart Energy Efficient Buildings, which aligns BDVA SRIA, FIWARE architecture, SAREF, HAYSTACK, and BRICK schema vocabularies (among the many others), and enable B2B sovereignty preserving multi-party data exchange, while providing full interoperability of big data enablers with smart buildings standards and addressing privacy and cyber-security constraints ii) upscale a number of TRL 5-6 technology enablers, such as sovereignty-preserving DLT/off-chain data governance, big data pipeline orchestration, IoT/edge AI-based federated learning and visual analytics and deploy them within the TRL 7-8 MATRYCS workbench iii) deliver a TRL8 open modular big data cloud analytic toolbox as front-end for one-stop-shop analytics services development iv) validate such framework through the deployment of analytics services focusing on digital building twins, improved buildings operation, building infrastructure design, EU/national policy assessment for energy efficiency investments on 11 large scale pilots by different stakeholders (facility managers, ESCOs, financial institutions, construction companies, municipalities, electricity grid and DH operators, policy makers) v) setup the BDA Alliance as a vibrant data-driven ecosystem for attracting new data hubs and SME service providers, enabling thus EU-wise take-up and replication