The 3 key actions that should be taken when data modeling in Salesforce during a migration from a legacy client-server app with a relational database are:

A. Identify data elements to be persisted in Salesforce.
B. Map legacy data to Salesforce objects.
D. Work with the legacy application owner to analyze the legacy data model.

Explanation:
A. Identify data elements to be persisted in Salesforce:

It’s crucial to determine which data from the legacy system will be required in Salesforce and which data may be outdated or irrelevant. This step ensures only the necessary and useful data is migrated, optimizing data storage and performance in Salesforce.
B. Map legacy data to Salesforce objects:

Once you understand the legacy data model, the next step is to map that data to Salesforce standard objects (like Accounts, Contacts, Opportunities) wherever possible. Leveraging Salesforce's standard objects helps ensure better integration with Salesforce's out-of-the-box functionality.
D. Work with the legacy application owner to analyze the legacy data model:

Collaborating with the legacy system owner is essential to fully understand how data was structured in the legacy system. This collaboration helps ensure you capture all necessary relationships and business logic when designing the data model in Salesforce.
Why the Other Options Are Less Suitable:
C. Map legacy data to Salesforce custom objects:
While some custom objects might be necessary, the primary goal should be to map as much as possible to standard Salesforce objects to maximize the use of native Salesforce functionality. Custom objects should only be created when there's no existing standard object that fits the data or business process.

E. Implement legacy data model within Salesforce using custom fields:
You should not aim to replicate the legacy data model exactly in Salesforce. Salesforce’s platform offers its own way of structuring data with standard objects, relationships, and functionality. Custom f...