Interface Component
An interface component maps a business process from the billing point of view. It defines which business transactions are represented by a class of billable items (such as deferred revenues and clearance of down payments). Interface components constitute the interface for a class of billable items.
SAP supplies preconfigured interface components that can be used immediately. These include basic components required for a record type as well as additional optional components that you can add to a class.
Note
You cannot use customer-defined interface components.
You can find an overview of available interface components in Customizing for Contract Accounts Receivable and Payable under 
Convergent Invoicing
Basic Functions
Billable Items
Billable Item Classes
Define Interface Components
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When you define billable item classes, you assign interface components to the classes. On the basis of this assignment, the system generates interfaces in which it automatically integrates the fields of the interface component. An interface, in turn, comprises function modules that transfer the data as well as tables in which the system stores the data.
Note
Some interface components correspond to invoicing functions or augment them.
Structure
Initially, an interface component is comprised of such information as an interface name and a description. It can also have a data element that documents the interface. Going further, an interface component is also defined by the following settings:
The assigned structures
Structures are assigned based on the record type and the status. You can also define that entries that do not belong to the record type of the main item are only active conditionally.
Prerequisite components
This setting indicates which interface components function as prerequisites. The basic components are not listed here; these are defined separately.
Program Enhancements
These are function modules that the system calls at the defined events. The function modules are used for enrichment and checks.