Transforming a data model from a Relational Database Management System (RDBMS) to a graph database requires significant changes, including replacing tables with node labels, rows with nodes, and columns with node properties. Foreign keys are replaced with relationships between nodes, and data with default values is removed. Additionally, denormalized and duplicated data may need to be pulled out into separate nodes for a cleaner model. Indexed column names can indicate array properties, and JOIN tables are transformed into relationships. The goal of these transformations is to achieve flexibility in arranging data in an easy-to-understand way.