This working paper inaugurates the "Technology Fundamentals for Digital Finance" series, concentrating on the technical aspects of financial Digital Assets. The series aims to facilitate the use of a clear terminology in a nascent platform-oriented paradigm of financial infrastructures, by laying the groundwork for technical discussions on digital asset standards. The paper introduces a conceptual model named ASAP (Access, Service, Asset, Platform) for Digital Asset Platforms (DAP), leveraging insights from IT industry practices and experiments by central banks. The ASAP model is illustrated through examples and use cases of tokenized assets, to demonstrate the possible usage and merits of modeling Digital Asset Platforms with four layers. Just as the utilization of a seven-layer model (often refered to as TCP/IP) has been fundamental to the interoperability of the internet, it is anticipated that the four-layer ASAP model for Digital Asset Platforms will similarly promote cross-platform interoperability, including across various jurisdictions, paving the way for a more cohesive digital asset ecosystem.