External objects are similar to custom objects but they map to data that's stored outside Salesforce. Salesforce Connect uses external data sources to access data that's stored outside your Salesforce organization1. This way, UC can comply with data residency requirements and avoid datastorage issues.
Salesforce Connect allows Salesforce to seamlessly integrate with data that is external to the Salesforce platform, which in this case is the legacy CRM and ERP applications. External objects provide a real-time view of this external data,allowing UC to view and report on it as if it were stored natively in Salesforce, without actually storing it in Salesforce.
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Salesforce Connect allows for the integration of external data in real-time without storing it in Salesforce, using external objects which function like standard Salesforce objects. This would meet UC's need to view and report on Invoice, Order, and Inventory data on-demand, adhering to data residency requirements. Salesforce Connect is designed for such scenarios, offering a solution that avoids data storage within Salesforce while providing access to external data as if it were native. This is in line with Salesforce's best practices for external data integration.