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Frequently Asked Questions

What is ALE?

Application Link Enabling (ALE) is a set of business processes and tools that allow applications on different computer systems to be linked. This can be done between different SAP systems as well as between SAP and non-SAP systems. In a single SAP system different applications are integrated via a single database (e.g. finance, sales, production, human resources). However, many companies do not have just one integrated system but a distributed environment with different applications running on different systems. To run the whole business in such an environment, the distributed applications have to be linked. This can be done through Application Link Enabling (ALE). ALE provides distributed business processes that can be used to link the applications on different platforms. There are some ALE business processes delivered in the standard SAP system. Furthermore, there are tools that can be used to change the existing ALE business processes or to implement new distributed business processes. Besides the business processes, there are special ALE services that are required to set up and control a distributed environment. These services include a distribution model, business object synchronization, and tools for monitoring or error handling. ALE is a major part of SAP's Business Framework Architecture. Besides the basis middleware, that provides the communication between components, and the interfaces (BAPIs), ALE business processes and ALE services enable the cooperation of the single components within the framework. That makes ALE the glue of the Business Framework.

With ALE, companies get the opportunity to improve business performance and to solve organizational or technical issues by:

  • Increasing Flexibility: Through distribution you can decentralize your business, enabling local units to operate independently from each other. This flexibility enables the local units to return better business results than in a centralized environment. They have the necessary flexibility to optimize business processes in different organizational units and can ensure that information systems can handle the speed of change in rapidly expanding markets. Distribution allows a high level of freedom, provided that this level of freedom has been clearly defined. On the other hand, some companies, that already have a distributed organization with different computer systems in the local units, have the opportunity to link their units through ALE business processes. This enables them for example to provide a 'one face to the customer' approach. Another area that can benefit through ALE are virtual organizations (partnerships between independent companies, joint ventures and mergers and acquisitions). Of course, in many cases an integrated solution based on a single system is not possible at all. Some applications used by a company cannot run on the same computer system. This includes legacy systems or complementary software. It may also be possible that a company uses different SAP industry solutions or specific country solutions, which do not run on the same SAP System. If these applications run on different systems, they cannot be linked by a central database but have to use a special integration mechanism like ALE. In this way, ALE also links SAP Core Systems to other SAP components like CRM, Business Information Warehouse or APO.
  • Reducing Costs: Besides the benefits of having an improved flexibility in setting up the whole business processes, ALE may also reduce costs, in particular costs of upgrading. If the whole business is run on one integrated system you have to upgrade the whole system, even if only one part of your company (e.g. human resources) requires an update. So the entire company is affected by the upgrade project and all users have to be trained for the new release. Within a distributed environment with release independent interfaces, like those provided by ALE, you can focus the upgrade project on that part of the company that has to be upgraded. The other parts of the company are not involved and need no training. This can save a lot of money. Furthermore, existing investments are protected. Another cost factor for distribution might be communication costs. For an overseas connection, it can be more expensive to provide online access to one central system (T1) than to connect distributed systems to each other (64K line).
  • Increasing Security and High Availablity: There might also be some technical reasons for distributed systems. If some parts of the business have special requirements for security of data access (e.g. human resources), this can be set up much safer on a standalone system, which is, however, linked to other parts of the company through distributed business processes. A similar example is high availability. High availability is usually required by the operations part of the company (production, logistics), but not by other areas (e.g. financials, human resources). In a distributed environment high availability can be set up for specific parts of the environment instead of for the whole business. This can also reduce costs. In a distributed environment, you can not decrease the overall workload of the systems but you can separate the user workloads on different systems. Through this scalability you can improve performance. Another benefit of distributed systems is that if a technical failure occurs on one system, all other systems continue to operate. Only a small part of the business is disrupted by the error. On one central system such an error would disrupt the entire business.

When should ALE be used?

Besides the benefits of ALE there are also reasons not to distribute:

  • The functional scope in a distributed environment is restricted. Not all functionality that is available in an integrated SAP system can be used with distributed systems in the standard yet. Although ALE provides tools to create new ALE business processes or to enhance existing business processes, this does involve additional expenditure.
  • Each company needs some organizational standards and data harmonization. In a distributed environment, less standards are required than on a single integrated system. However, in a distributed environment the maintenance of the standards and the data harmonization is more difficult than on a single system.
  • The administration of decentralized systems is more expensive. Support and service costs for hardware and software in decentralized systems are higher than these costs in a single centralized system.

ALE should be used in a company if the benefits of ALE for this company outweigh the reasons against distribution. For this you always need to carry out a company specific investigation, in which you also should consider the culture of the company. ALE is good for some companies, but not for all.

What is the relationship between ALE and middleware?

There are many such messages, the most common of these include a customer sending a purchase order message to a vendor, or a vendor sending an invoice message to a customer. Classic EDI is mainly restricted on the exchange of transactional data, no master data or configuration data. In most cases, EDI replaces the transfer of paper copies of these documents. Via the messages ALE business processes can be implemented between business partners. The EDI messages also use the ALE services. For the communication between different types of systems special EDI messages are defined as standards for inter company communication. There are many standards for these messages - in the United States, the ANSI X.12 standard is the most prevalent, in Europe, the UN/EDIFACT standard is used. For sending EDI messages the information has to be converted into an EDI standard. With SAP systems this is done by EDI subsystems. This conversion is the only difference between EDI messages and other messages used in ALE business processes. The processing of these messages on the SAP System is the same as the processing of other ALE messages.

Which ALE business processes are available?

ALE business processes are integrated business processes that run across distributed systems. This can be two different SAP systems, links between SAP and non-SAP systems, SAP and Web-servers (Internet Application Components) or SAP and desktop applications. The links between the systems may be loosely (asynchronous) or tightly (synchronous) coupled. These business processes are release-independent and can run between different release levels of the systems. Many SAP applications offer ALE distribution processes, for example Master Data Replication, Accounting, Logistics and Human Resources.

When should synchronous or asynchronous links be used?

When distributed applications are linked by ALE business processes, the question often arises as to how tight the link should be. Synchronous and asynchronous links have both advantages and disadvantages:

  • Synchronous links have the advantage that the sub-process on the server can return values to the sub-process on the client that has started the link. Problems with synchronous links occur if the communication line or the server is temporarily not available. If this happens, the sub-process on the client can not be finished (otherwise there would be data inconsistencies).

Example: There is a logistics system and a financial system. Every stock movement in logistics has to be posted in the general ledger of the financial system. If the link between logistics and finance is synchronous, no stock movement can be recorded in the logistics system if the communication line to the financial system is down.)

Because of this, synchronous links are usually used if the client only wants to get some data from the server and the sub-processes on the server do not have to write any data to the database.

  • With asynchronous links the sub-process on the client can be finished even if the communication line or the server is not available. In this case the message is stored in the database and the communication can be done later. The disadvantage of asynchronous links is that the sub-process on the server can not return information to the calling sub-process on the client. A special way for sending information back to the client is required. In addition, a special error handling mechanism is required to handle errors on the receiving side. Asynchronous links are used if a synchronous link is not applicable. For the problems with sending return information to the client and with error handling there is some support from the ALE services.

Why does SAP use ALE instead of database replication or distributed databases?

Database replication is another possibility for doing business object synchronization. However, there are some major disadvantages with database replication. At the moment database replication is database dependent and release-dependent within one database. This makes database replication impossible for the use with non-SAP systems and even for the replication between SAP systems, you have to make sure that all systems are running on the same SAP release and the same database release of a single database vendor. Furthermore, with database replication you cannot do things like field conversions or version changes. ALE does not have these shortcomings because it offers application driven data replication independent of the underlying database.

Another technology, distributed databases, is no alternative for ALE at the moment, either. There are some good results of distributed databases available, but the performance is far from sufficient for using it with larger applications like SAP.

How can I serialize IDoc processing?

There are various procedures for processing IDocs in a serialized way, that is to process them or transfer them to the application in a certain sequence. Depending on your respective requirements, one of the methods proposed in note 752194 may be suitable for the required purpose.

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