许多大企业把整个SAP system分布在多个instance上,每个instance专注于特定的业务.
例如: plant中的物料采购在一个本地的instance上进行处理(the local system).
向供应商付款和总帐处理在公司中心instance上处理(the central system).

分布(distribute)不是简单的数据分割!!!
分布就是把数据分布在多个地点,但同时又能保证数据在整体上的一致性和完整性.
分布用到分割技术, 但是分布不是简单的分割.为了保证不同地点的数据的完整性
和一致性different systems利用ALE进行沟通.
The ALE concept always relates to an enterprise structure with areas that have central tasks
and areas with tasks that are decentralized.

 It may be practical for organizations to use separate application systems so that application components can be installed and operated on decentralized systems that are technically independent of each other.
 The ALE concept supports the implementation and operation of distributed SAP applications. It is based on business-controlled messaging with consistent data storage on loosely coupled systems. The applications are integrated through the message exchange, not via a central database.
 To implement a distributed, yet integrated system, the customer must specify in a logical model, which applications are to run on which systems and how the applications are to exchange data with each other.
 On the technical side, the data exchange is carried out via IDocs (intermediate documents) as used in the EDI (Electronic Data Interchange) interface. On the application side, EDI supports information exchange between R/3 systems in different enterprises, whereas ALE supports information exchange within one enterprise. The ALE distribution mechanism is similar to the EDI mechanism. In ALE, business processes are distributed at the transaction level.

 The procurement of materials via the plant in a company code can be handled in a local system. However, payments to vendors and the general ledger are managed in a central system.
 In order that both organizations use the same master data, the head office distributes the master data to the local system. Thus the transaction data in the local systems for which IDocs exist can be sent to the head office without inconsistencies.
 Examples of data that can be distributed:
­ Master data: Customers, vendors, G/L accounts, cost centers, cost elements, activity types
­ Transaction data: Incoming invoices, outgoing invoices, Financial Accounting line items, Controlling documents
 The SAP standard system is delivered with some ALE scenarios. For example:
­ Central contract management in Purchasing
­ Distributed Inventory Management
­ Central Materials Management master data
 The message types required for the distribution via IDocs are also delivered by SAP. You can also define your own ALE scenarios.
 Business to Business Procurement works through ALE with an R/3 backend system