Developing a Web Service Based on Existing Functions (Inside-Out) 
With the inside-out approach, independent function modules that were implemented as RFC-enabled function modules, as function groups, or as BAPIs are provided as a Web service. The Web service can be used across the entire Internet using standard protocols and can easily be added to any development environment.
Prerequisites
The user has been assigned the appropriate Authorizations.
Features
You provide Web services on the AS ABAP using the service wizard.
The Web service properties are defined in a preset, selectable profile. The values assigned through a profile can be changed in the Object Navigator of the ABAP Workbench.
You can assign features – such as the authentication level, for example – to the service definition in abstract form. The technical details of these features are specified in the Web services configuration.