Special Edition Using SAP R/3, Third Edition

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Special Edition Using SAP R/3, Third Edition - CH 3 - Exploring R/3 Architecture Page 10 of 26 to whether the transfer is between applications or with a mainframe host. Synchronous CPI-C The transfer of the CPI-C commands and the management of transmission between applications or to a mainframe host takes place in a mutually dependent mode in a fixed-time relationship. This process is known as synchronous communication. If it is not possible to use synchronous communication, the alternative is asynchronous communication, which may be necessary in these types of situations: Starting a process on a target system has to be carried out manually--for example, because particular media have to be loaded manually. The target computer temporarily can’t accept or provide data. Asynchronous Q-API The R/3 system can maintain data in buffers that are queued and waiting for a suitable moment to be transferred to the receiving computer. This moment can be defined by a schedule or determined by the availability of the receiving computer. These queues can be freely integrated into any of the SAP application programs. The mechanism of choice is Queue Application Programming Interface (Q- API). Two types of data format are supported under Q-API: The batch input format defined for accepting external data records into the R/3 system, which is directly recognized and entered into normal interactive transactions Data in a format that has been defined for the receiving program to suit the specific situation RFC and RPC Protocols The standard business functions of the R/3 system can be called and accessed freely without any special provision by the user apart from the normal business authorization procedures that may limit access of certain users to specific functions. However, your implementation may include some functions that were specially written in the ABAP/4 programming language to perform functions unique to your organization. The discussion in Chapter 29, "Developing ABAP/4 Programs with the R/3 Workbench," outlines the method of building these special-function modules. The Remote function call (RFC) is the SAP ABAP/4 programming language implementation of the remote procedure call (RPC) protocol, which is the standard adopted for accessing special-function modules. The following types of special functions can be accessed by using the RFC protocol: Functions residing in the R/3 system special-function library External programs called from within ABAP/4 applications file://J:\prodinfo\MEMBERS\MA\ir057.html 3/23/01
Special Edition Using SAP R/3, Third Edition - CH 3 - Exploring R/3 Architecture Page 11 of 26 Function modules that reside in other computers RFC can be used by an R/3 application to communicate in both directions with other R/3 applications, with R/2 programs, and with external applications running on other systems. The R/3 runtime system controls any communications with other computers initiated by RFC procedures. Environments in the C language typically use RFC methods. Asynchronous RFC Features RFC recognizes the syntax and usage for calling normal- function modules in the R/3 system. The user does not have to know that the function is using a remote computing resource. Calls can be dynamic and do not entail setting up static communications modules or stubs. A system table is used to recognize the destination name of a remote call and to set up a suitable type of connection with the partner. When the R/3 system is installed, the partners can be configured as logical target systems that the system specifies later in detail. The RFC protocol is available in the TCP/IP and the Systems Network Architecture (SNA) LU6.2 network protocol. An API for an external C language program can be set up by using an RFC. R/3 function modules can be called by external programs by the same mechanism. Error handling is done by a standard exception mechanism that allows remote debugging and troubleshooting across system boundaries. The RFC protocol supports all ABAP/4 data types, such as single fields, data structures made from data objects, and tables. The protocol is fully integrated into the ABAP/4 R/3 Program Development Workbench. A software development kit, RFC-SDK, is available to support the creation of non-SAP programs that recognize remote function calls. RFC's Delta Management Functions The overhead cost of communication between programs can be reduced by RFC’s Delta functions. The Delta functions concentrate on detecting and responding to small changes. A function typically needs to transfer a table of data as one of its parameters. The Delta method allows a first full transfer and then subsequently transfers only data elements that have changed. These changes are communicated by a transfer of log tables that carry details of the changes made by the transactions. The RFC Delta management functions offer the following benefits: The target system executes the RFC calls in the same order and within the same program context as in the calling system. Each RFC is executed only once. The status of an RFC call can be queried at any time to access the data in the log tables and ascertain the progress of the transaction. A callback function can be activated to invoke further activities in the calling system. file://J:\prodinfo\MEMBERS\MA\ir057.html 3/23/01
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