This document aims to present the methodology for building a DECODE ontology useful to support the DECODE goals, especially in relation to smart contracts i) for checking compliance in the personal data protection domain; ii) for managing the data sovereignty; iii) for the creation of data commons. A little proof-of-concept is presented in this deliverable. It is not an objective of this work to build a DECODE ontology that needs, by definition, at least one year of analysis, modelling, representation, evaluation, validation and refinement. The main aim is to provide a methodology for building DECODE ontology, to evaluate pros and cons concerning technical solutions, to provide some examples integrated with the scenario of DECODE.