What is the role of DAX in Power BI?

DAX, or Data Analysis Expressions, plays a crucial role in Power BI primarily for performing calculations and data modeling. It is a formula language designed specifically for handling data in Microsoft Power BI, Excel, and other Microsoft tools that support data analysis.

DAX allows users to create calculated columns, measures, and custom tables using a syntax that resembles Excel formulas. This capability enables the construction of complex calculations and aggregations that can be applied to your data models, thereby enhancing the analytical power of your reports. With DAX, users can perform operations like filtering data, calculating year-to-date totals, and performing time-based analysis, all of which are critical for deriving insights from data represented in visualizations.

The other options refer to functionalities that are either outside the core purpose of DAX or concern different aspects of Power BI. Customizing the user interface involves design aspects that DAX does not address. Managing user permissions is related to security and access control, which is handled within Power BI settings, not through DAX. Connecting to external data sources is part of Power BI's data import capabilities, which involves data connections and queries but does not involve DAX. Thus, the primary role of DAX is firmly within the realm of calculations and data modeling.