Any data model, data source, or calculated value built in Flow is available via the REST API... that includes the raw data that still resides in the underlying, connected data sources. Without knowing the structure or naming convention of those SQL tables or data historians, Flow can provide you with millions of data values.
Dive deeper into Flow's Prove It! presentation with this UNS+ webinar. Topics tackled include how to add data and information governance to the unified namespace, provide historical data access via a federated database, and ensure that engineering context is added to the UNS.