Data Modelling is the “make or break” stage of Power BI development. If you build a strong dimensional data model (usually a star schema), your DAX will be much simpler, more performant and will produce accurate results. Conversely, get your data model wrong and even expert DAX skills may not be sufficient to overcome the problems created. In addition, good data models are easier and cheaper to maintain and document.
How to submit your solution
Each workout will provide instructions as to what you will need to submit. Depending on the nature of the workout, it likely will be some combination of a screenshot of your data model, your PBIX file and/or Power Query or DAX code.