To retrieve changes from the human resources system, you could call out from Force.com using HTTP or a REST Web service call, as described in Chapter 10. But when you would do this is not clear because Force.com does not receive notifications when the human resource system is updated. Polling the system for changes would be inefficient and quickly hit governor limits on Web service callouts.
Instead, use the Enterprise API to connect to Force.com and upsert the modified records. Begin by updating a single field called
Active__c, indicating whether the employee is active. After you get this field working, move on to support additional fields such as the address and phone fields of the Contact record.
The first problem is ...