Data is the most important property for bringing innovation and digital transformation. In Japan, data-driven society is one of the most important concept for the future society referred in Society 5.0, DFFT (Data Free Flow with Trust), and National Data Strategy of Japan. Several public and/or industrial domains have already established data ecosystem including data sharing platforms. However, there are many scenarios and applications which cannot be supported by the domain-specific data platforms. For example, disaster response, tourism, GHG (Greenhouse Gas) management such as the Scope 3 protocol, supply chain management support, and smart city are among them. So, we need a cross-domain data-exchange platform to support these applications. The objective of this paper is to propose "DATA-EX (data exchange)", which is a platform which is under development and will be operated by Data Society Alliance (DSA), and works as an infrastructure for cross-domain data exchange consisting of open standard specifications and guidelines for data exchange and platform operation, software systems based on the standards, and governance rules for the operation of DATA-EX. This paper presents definition, objectives, basic strategies, and architecture of DATA-EX, and its current status and future plan.