Use APIs to connect and communicate with any software application.

There are 2 types of API protocols that are popular.

• REST APIs: REST relies on a client/server approach that separates front and back ends of the API and provides considerable flexibility in development and implementation. REST is stateless, which means the API stores no data or status between requests.
• SOAP APIs: The simple object access protocol (SOAP) is a messaging standard defined by the World Wide Web Consortium and broadly used to create web APIs, usually with XML. SOAP supports a wide range of communication protocols found across the internet, such as HTTP, SMTP and TCP/IP.

SAP does not support the above protocols “As Is” but has a slightly different protocols to connect with the SAP system. Below are some of the ways by which the connection to an SAP system can be established:

• SAP Java Connector is a middleware product offered by SAP {SAP JCo} that enables a Java application (ServiceNow SAP Connector Jar) to communicate with SAP systems via RFC/BAPI protocol. The SAP JCo supports both communication directions: inbound Remote Function Calls (Java calls ABAP) as well as outbound Remote Function Calls (ABAP calls Java). SAP DocumentationLink.
• IDOC - IDoc is an SAP object that carries data of a business transaction from one system to another in the form of electronic message. IDoc is an acronym for Intermediate Document. The purpose of an IDoc is to transfer data or information from SAP to other systems and vice versa. 
• OData is an Open Data Protocol used in web technologies. OData is used by SAP to make SAP data accessible to other platforms so that the non-SAP users can also access this data to develop web applications, websites, mobile apps, etc.