Optimizing the data source by reviewing and refining complex calculations and data relationships The initial approach to resolving slow query performance due to a data source should be to optimize the data source itself. This includes reviewing complex calculations, data relationships, and query structures within the data source to identify and address inefficiencies. This optimization can significantly improve query performance without needing more drastic measures. Option A is incorrect as restructuring the underlying database is a more extensive and complex solution that should be considered only if data source optimization does not suffice. Option C is incorrect because replacing the data source with a pre-aggregated summary might not be feasible or appropriate for all analysis needs. Option D is incorrect as increasing extract refresh frequency does not directly address the root cause of slow query performance in the data source itself.