In the framework of the EUROfusion Consortium, the Work Package Heating and Current Drive (WPHCD) is undertaking the development and design of the DEMO Heating and Current Drive (HCD) system, supported by the Work Package Plant Level Systems Engineering, Design Integration and Physics Integration (WPPMI). As the DEMO project is in the Pre-Conceptual phase, its development is dominated by uncertainties on system requirements, and by different DEMO designs and scenarios. In this context, a number of outstanding technology and physics issues, e.g. related to safety, neutronics, performance and reliability, need to be resolved using an integrated approach. For coping with these boundary conditions, we present an initial analysis of HCD requirements and functions through the development of a System Architecture model, i.e. through describing the HCD system in terms of its functions and their interdependencies. Scope of the work is to address uncertainties i) associated with different reference scenarios (e.g. pulsed and steady-state tokamak) and operational concepts; ii) related to system performances. The assessment is part of integration activities, consisting of both systems engineering methodologies and design analysis, all aiming to ensure consistency in the overall EU DEMO plant design.