WP4 is focused on developing interoperability between available resources both at a physical level, creating the H2IOSC National Cloud Infrastructure and at a semantic level, by translating the state of knowledge with respect to the resources offered by each RI into a common semantic interdisciplinary and interoperable representation (i.e.: the H2IOSC reference ontology). WP4 will focus on the alignment (i.e.: collection, cleaning, mapping, and modeling) of resources gathered by the 4 participating RIs. To facilitate the alignment, a common mapping schema will be deployed to support the data transformation process: from the original format(s) towards the H2IOSC reference ontology. The actual H2IOSC-RO (Reference Ontology) development is meant to create a level of interoperability between resources gathered by RIs, by providing a shared Conceptual Reference Model to represent information coming from heterogeneous sources using a common vision. The development workflow involves: i) analyzing the state of the art and focusing on common problems related to the management of information provided by the RIs; ii) providing a pipeline of validated actions and guidelines on the assessment and semantization of data; iii) offering practical methods for heterogeneous data integration, including transformation and validation, fostering resources exploitation and reuse.