BTE's or Business Transaction Events are a special type of extension for the FI Module.Like SD's Customer Exits, BTE's allow customer to adapt the system to their needs.
BTE's are based in the following principles:
Business Transaction Events and Business Add Ins rely on the same concept. Nevertheless, there are some differences between them:
Two types of interfaces exist:
These interfaces inform about particular events (such as a document created), and the resulting data of these events are made available to external software; this software can not return data to the SAP System. Examples of this type of interface include:
This type of interface does not change the standard processing.
These kind of interfaces are generally used to send business processes to a customer created control; that is, process interfaces replace the standar process.
With Process Interfaces you can modify the standard behaviour of the SAP System. If for some reason the standard procedure does not match the client needs, a Process Interface may be implemented and it will replace the standard process flow.
If you would like more detailed information, as well as an implementation example you should check this document from SDN.