Are all objects on sequence diagram should be designed in class diagram?

Question

I'm working on sequence & class diagram for education website, should all objects in sequence diagram be a class in Class diagram?

For example in sequence diagram for registration process I need an object called "Data Base" which needed for saving information of user, should "Date base" be a class in class diagram? and what can be its functions? Is it just load & save?

Answer 1

Yes, the Database would be a class in Class Diagram and its functions can be validation() , generatingErrorMessage() etc.