Power BI report visualizations and dashboard tiles are built on top of datasets, and each Power BI report is associated with a single dataset. Power BI datasets can import data from multiple data sources on a refresh schedule or can be configured to issue queries directly to a single data source to resolve report queries. Datasets are therefore a critical component of Power BI projects and their design has tremendous implications regarding user experience, query performance, source system and Power BI resource utilization, and more. 

The dataset designer is responsible for the data access layer of the Power BI dataset, including the authentication to data sources and the M queries used to define the tables of the data model. Additionally, the dataset designer defines the relationships of the model and any required row-level security roles, and develops the DAX measure expressions for use in reports, such as year-to-date (YTD) sales. Given these responsibilities, the dataset designer should regularly communicate with data source owners or SMEs, as well as report authors. For example, the dataset designer needs to be aware of changes to data sources so that data access queries can be revised accordingly and report authors can advise of any additional measures or columns necessary to create new reports. Furthermore, the dataset designer should be aware of the performance and resource utilization of deployed datasets and should work with the Power BI admin on issues such as Power BI Premium capacity.

As per the Power BI team toles diagram, there are usually very few dataset designers in a team while there may be many report authors. This is largely due to the organizational objectives of version control and reusability, which leads to a small number of large datasets. Additionally, robust dataset development requires knowledge of the M and DAX functional programming languages, dimensional modeling practices, and business intelligence. Database experience is also very helpful. If multiple dataset designers are on a team they should look to standardize their development practices so that they can more easily learn and support each other's solutions.