
Explanation
Graphical user interface, text, application Description automatically generated

Box 1: Use Virtual tables
A virtual entity is a custom entity in Dynamics 365 Customer Engagement (on-premises) that has fields containing data from an external data source. Virtual entities appear in your app to users as regular entity records, but contain data that is sourced from an external database, such as an Azure SQL Database. Records based on virtual entities are available in all clients including custom clients developed using the Dynamics 365 Customer Engagement Web Services.
Box 2: Use Dynamics 365 Web API.
Dynamics 365 Web Services API: Many times, straight database-to-database integrations aren't a possibility.
In these cases, the development of a solution may depend on utilization of the Dynamics 365 Customer Engagement web services API (Application Programming Interface).
Reference:
https://docs.microsoft.com/en-us/dynamics365/customerengagement/on-premises/customize/create-edit-virtual-e