What is the difference between Outlook MAPI and Exchange Web Services (EWS)?

Outlook MAPI is a set of interfaces used to access resources within the Outlook client, such as reading emails from the local .ost file. In contrast, Exchange Web Service (EWS) Development Guide is designed to access resources directly from the Exchange server. MAPI requires the Outlook client to be installed, while EWS does not depend on a local Outlook installation.