Perform database tasks in service

I am going to develop an application that should have service to run even though UI is not present. So I was thinking that should I do every database task in service or UI and service should perform them together?

I know it is possible to use database so that UI and service both can use, but I want to know which one is appropriate and has lower CPU usage. Which one is better: a shared database between UI and service or passing data from UI to service to perform all tasks in service?