This video contains new content that is related to the Connecting to Data Sources section, and covers new features that have been added in late 2018.
Composite models allow you to do two new important things: have multiple DirectQuery data sources in the same model, and to mix DirectQuery and Import data sources in the same model. This brings a number of benefits: not only does it give you more flexibility for modelling when you’re working in DirectQuery mode, but it will also improve query performance because if the data in a table does not change much you can use Import mode. It will also improve refresh performance because you can use DirectQuery mode for large tables where query performance is less important.
A related feature to composite models is aggregations. This feature helps query performance by allowing you to store pre-aggregated data in Power BI, which can then be used by Power BI when it runs queries that request aggregated values from another table. It will be particularly important when you have a large table stored in DirectQuery mode because you will be able to store pre-aggregated data for that table in Import mode.
Finally, incremental refresh allows you to avoid having to refresh all the data in a table when you do a refresh—instead, it allows you to just refresh the data in a table which you know has changed. At present, this feature is only available in Power BI Premium.
