techPaper.txt

-- How can external systems be integrated into SAP and which interfaces does the ERP system offer?
RFC, BAPI, IDoc, SOAP, REST

RFC – Remote Function Call
The classic way for communication between non-SAP systems and SAP is, according to SAP itself, the RFC interface. 
RFC interfaces are also often used to communicate between SAP systems itself. Put simply, RFC is a remote function
call. The RFC interfaces for integration have been available since SAP/R3 until today.  With RFC, there is an RFC 
client and an RFC server, whereby the client calls a function on the server. The function is executed on the remote 
system.  In an RFC coupling, both systems can act as server and client.  The call of an RFC function is synchronous, 
so that it is especially suitable for processes in which decisions or data are directly required for production. 

BAPI – Business Application Programming Interface
The basic concept of BAPIs is object-orientation. BAPIs make the business objects available in the SAP system for 
access by external systems. Business objects represent real objects such as orders, customers or articles. The instances 
are accessed exclusively using methods provided by the business object. Technically the method is called on the basis 
of the RFC interfaces. The instance to which the calls are made is determined by key fields (customer number, and so on).
Business Object Repository(BOR) and Remote Function call

The IDoc (Intermediate Document) is an SAP file format. It is intended for transfer of transaction data. The structure 
of an IDoc is prescribed by the IDoc type and defines the exact length and position of fields in the file. The IDoc 
is divided into a header line, any number of data segments and status records. In contrast to the RFC interfaces, 
communication via IDocs is always asynchronous. The sender creates an IDoc with data according to the specification 
of the IDoc type and transfers it to the target system. The receiving system accepts the IDoc and inserts it into 
the processing buffer for IDocs, from which the documents are processed successively. IDocs are a very old and proven 
method of communication and are especially suitable for transferring master data and posting records. 

SOAP web services are one of the newer technologies for connecting SAP. Since version 7.0 and the introduction of SAP 
NetWeaver, Web services have been standard for interfaces.  SOAP is a pure web technology and functions are called 
using the HTTP protocol. RFC Functions are also made available via the SOAP interface. The client receives detailed 
information about the functions and their parameters via the WSDL file (Web Service Description Language). The WDSL 
file can be retrieved via a defined URL.  Web services are created in SAP using WebDynpro and connected to ABAP 
programs and RFC interfaces. RFC functions can also be published as Web services using other solutions (such as SAP MII). 

REST API
For some years now, the SAP Gateway has had the functionality to provide ABAP functions and RFC interfaces in the form
of a REST API. REST has some advantages over SOAP, but is similar in technology, since it is also a function call via 
HTTP protocol. Compared to SOAP, REST is easy to call from various platforms, transfers pure human-readable data in 
JSON or XML and is faster and saves resources. In the basic idea of REST, an object is accessed via REST, not its methods. 
The state of the object can be changed by the REST access. The change is caused by the passed parameters. A frequent 
application is the connection of the SAP PI via the REST interface.
CRUD: Create(POST), Read(GET), Update(PUT, PATCH), Delete(DELETE)

OData (Open Data Protocol) is an ISO/IEC approved, OASIS standard that defines a set of best practices for building and 
consuming RESTful APIs. OData helps you focus on your business logic while building RESTful APIs without having to worry
about the various approaches to define request and response headers, status codes, HTTP methods, URL conventions, 
media types, payload formats, query options, etc. OData also provides guidance for tracking changes, defining 
functions/actions for reusable procedures, and sending asynchronous/batch requests.
OData RESTful APIs are easy to consume. The OData metadata, a machine-readable description of the data model of the APIs, 
enables the creation of powerful generic client proxies and tools.

What is REST?
REST is acronym for REpresentational State Transfer. It is architectural style for distributed hypermedia systems.
REST also does have it’s own 6 guiding constraints which must be satisfied if an interface needs to be referred as RESTful. 
These principles are listed below.
1. Client–server
2. Stateless - Each request from client to server must contain all of the information necessary to understand the request.
3. Cacheable – Cache, non-cacheable
4. Uniform interface
5. Layered system - an architecture to be composed of hierarchical layers
6. Code on demand (optional) 
Resource - Any information that can be named can be a resource
Resource Methods - uniform interface
In simplest words, in the REST architectural style, data and functionality are considered resources and are accessed using 
Uniform Resource Identifiers (URIs). The resources are acted upon by using a set of simple, well-defined operations. 
The clients and servers exchange representations of resources by using a standardized interface and protocol – typically HTTP.

SAP OData
http://www.saplearners.com/model-your-first-odata-service/

SEGW - Gateway Service Builder
/IWFND/*, /IWBEP/*
/IWFND/MAINT_SERVICE - ACTIVATE AND MAINTAIN SERVICES
/IWFND/GATEWAY_CLIENT - Getway Client
/sap/opu/odata/sap/ZCREATE_CRUD_OPERATION_SRV/$metadata

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