Application Link Enabling (ALE) 
Application Link Enabling (ALE) is the R/3 technology that enables you to construct and operate distributed applications, sometimes in different countries. It involves the controlled exchange of business information between SAP applications with consistent data management. Application integration is achieved not through a central database but via synchronous and asynchronous communications.
ALE consists of three layers:
- Application services
- Distribution services
- Communications services
For transmitting data, ALE provides you with standard technical bases such as:
- X.400 as the e-mail standard
- X.435 as the application to application extension of X.400
- General messaging infrastructure with proximity to mail systems
- Messaging support using software such as Microsoft Exchange and Novell applications.
ALE must both satisfy customers’ needs today and remain open for future developments. It has therefore been designed to meet the following key requirements:
- Communication between different update versions is made possible
- Data exchange continues to run without maintenance after a release upgrade
- The technical format of a message is independent of the content
- Enhancements can be carried out simply, by the customer if necessary
- The application is detached from communication
- Non-SAP applications can be attached via communication interfaces
- R/2-R/3 and R/3-R/3 scenarios are taken into account
For full information on ALE, see:
ALE Consultant’s Guide
Implementation Guide for Application Link Enabling