Cloud computing are becoming new platforms for enterprise and personal computing as it is better in software delivery and pricing than the traditional platforms. The development of cloud computing technology has speeding up the SaaS since it provides a lower barrier for company with less budget for their information system infrastructure.
SaaS is a method of software delivery that allows data to be accessed from any device with an Internet connection and web browser . In fact, SaaS is an interface liked concept in OOP, which provides a method of function delivery that allows data to be accessed from other classes. One of the big difference between them are the clients who use it (locally or through network). However, SaaS is not RPC or CORBA architecture (programming language dependent).
Currently, There are two approach for the implementation of SaaS as API, which are RESTful and SOAP. REST uses HTTP/HTTPS with the standard GET, PUT, POST, and DELETE verbs, in contrast, SOAP can use XML to address almost any transport to send the request. I personally prefer the RESTful approach since it is much simpler than the SOAP approach.
The following video shows the difference between RESTful and SOAP.