Data Modelling in Power BI: Star Schema, Relationships and Why They Matter

Data modelling is the process of structuring and defining relationships between data tables to enable accurate and efficient analysis, particularly in tools like Power BI. A poorly designed model can slow down reports and introduce calculation errors, while a well-built one can cut report refresh times from minutes to seconds. Two common approaches are the flat single-table model, which is simple but becomes unwieldy at scale, and the star schema, which organises data into a central fact table linked to surrounding dimension tables. The star schema is widely preferred for its performance benefits, DAX-friendly structure, and scalability, though it requires careful planning around keys, cardinality, and filter direction. Understanding these fundamentals helps analysts build maintainable, accurate, and high-performing data models.