--All Web services are APIs but not all
APIs are Web services.
--Web services might not contain all
the specifications and cannot perform
all the tasks that APIs would perform.
--A Web service uses only three styles 
of use: SOAP, REST and XML-RPC for
communication whereas API may be exposed 
to in multiple ways.
--A Web service always needs a network
to operate while APIs don’t need
a network for operation.