SAP NetWeaver is just a term used for SAP system. All SAP systems are mostly running on NetWeaver. SAP PI is one of common integration tool like Biztalk and it is not necessary that all clients has SAP PI system for integration.
You should use Remote Function Call RFC in SAP system for integration. RFC is an interface provided by ABAP server and can be used for both synchronous and asynchronous data transfer. Remote Function Call (RFC Connection) between two systems. By creating a trusted RFC connection between two systems, it allows you to create trusted-trusting relationship between systems wherein, you can communicate and exchange information and data.
This can be consumed using an SAP .NET connector. A .NET Connector is known as a programming environment that allows communication between the Microsoft .NET platform and Systems. Using.NET connector, you can use SAP Remote Function Calls RFC and Web services, and allows you to write various applications like Web form, Windows form, and console applications within Microsoft Visual Studio .NET.
Other option that can be used in SAP to connect to different external applications is via BAPI. BAPI (Business Application Programming Interface) is defined as set of interfaces to object-oriented programming methods that allow developers to integrate third-party software with SAP ERP system.
Following steps are involved for BAPI creation:
Transaction SE11: Creating a dictionary structure
You can use (ctrl + F2) to check the structure and (ctrl + F3) to activate the structure.
Transaction SE37 Creating a Function module
Click on create button and enter the name of the function module. Enter the function group and short text. To save Function module, you need to click on save button at the top.
Creating the business object in SWO1 − Go to transaction SWO1 and enter the name of the BAPI you would like to create and click create.
You can refer to this link on user defined BAPI creation −