ABAP ALE FAQ'S

1. 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.

2. What are the benefits of ALE?

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

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 can not 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 can not 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.

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).

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.

3. 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.

4. What is the relationship between ALE and Middleware?

Electronic Data Interchange (EDI) is a term for the transfer of business messages between two systems.

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.

5. 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. The following list gives some examples:

• Master data replication:
  - Material
  - Customer
  - Vendor
  - General Ledger accounts
  - Bill of materials
  - ...
• Accounting:
  - Links to logistic systems
  - Distributed financial accounting
  - Distributed cost center accounting
  - Distributed special ledger
  - Profitability analysis
  - Distributed profit center accounting
  - Consolidation
  - Treasury
  - ...
• Logistics:
  - Reallocation of materials
  - Distribution of sales and shipping
  - Product data management
  - Purchasing contracts
  - Sales and operations planning
  - Warehouse management
  - Links to warehouse control systems
  - Links to production optimization systems
  - Links to transport planning systems
  - ...
• Information systems:
  - SAP Business Information Warehouse (BW)
  - Exchange of data between information systems
  - Web reporting
  - ...
• Human resources:
  - Human resources as a single component
  - Payroll results
  - Travel expense accounting
  - Links to time collecting systems
  - ...

However, these standard solutions may not fit 100% for a company. There may be differentiation in the business process or a required distributed business process is not supported in the standard.

If this happens, ALE provides tools that can be used to adapt a standard ALE business process or to create a new distributed business process.

6. Which ALE services are available and what do they do?

To integrate distributed systems you need more than a communication infrastructure and interfaces. Some additional services are required that are provided by ALE:

Business process harmonization:

Within system overlapping business processes multiple functions running on multiple systems are involved and connected through multiple interfaces. The processes are combinations of functions (sub-processes) running on the single systems.

(Example: A business process for customer order management involves functions in sales, manufacturing, warehouse management, finance, and so on. It is possible that the sales functions are carried out on another system than the manufacturing, the warehouse management or the accounting. Furthermore, some information exchange with the customer, a supplier or a bank may be involved in the process.)

ALE helps to coordinate the whole business process by defining it within a global model. In this model the business rules for the distribution are defined.

Via the model the sub-processes get to know which part of the overall process they have to do themselves and when they have to pass the process over to another system. Through this the whole business process gets harmonized.

Receiver determination:

For distributed business processes a sub-process on one application (client) has to start another sub-process on another application (server). It is important that the new sub-process is started on the right server.

Which server is the right one can not be defined by technical values, it depends on the business content of the process.

(Example: A sales system forwards customer orders to two different production systems. To which system a special sales order is forwarded depends on the entries in the sales order (this may depend, for instance, on the ordered material or on the customer). One sales order may also be split into two or more different orders that may be forwarded to different production systems.)

To notify the client which system is the receiver of the communication (server), ALE uses a distribution model.

From this model the applications get the information about the right server. There are special ALE BAPIs and function modules available for this. The receiver determination makes sure that the information is sent to the right places.

Business object synchronization (semantic synchronization):

If business processes run across distributed systems, they have to share some data to be harmonized.

This is data like business information data, master data or customizing data. If this data is changed in any of the distributed systems, other systems have to be informed about the change. There has to be some kind of subscription of the data.

ALE provides a special service for this data synchronization. This service can detect data changes and distribute the information to those systems that need to know about the change. This service also defines which data is shared.

You can determine which fields of a data object shall be common and which fields may vary locally.

Consistency checks:

For a business process running across two distributed applications there has to be some harmonization of the sub-processes in the single applications.

For making sure that the sub processes are harmonized there are special ALE consistency check tools. These tools help to find and repair inconsistencies. By this it can be ensured that the whole ALE business process works in the right way.

Monitoring:

For the monitoring of distributed processes it is not enough to monitor all activities on the single systems.

The overall business process has to be monitored. The ALE monitoring services provide detailed information about the communication process, the sub-process on the other systems and its results.

Database links are created between the business objects in question on the client and the server. This is especially important for loosely coupled applications with asynchronous links. In this case the server can not give return values back to the client directly so that the ALE monitoring is the only channel for feedback.

Error handling:

Another problem with asynchronous communication is error handling. If an error occurs on the server the calling process on the client may have finished already. So the server can not return the error message to the client.

A special error handling process required. This process is one of the ALE services. It uses workflow functionality to identify the error and to start the required error handling.

7. Synchronous vs. asynchronous links?

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.

8. Which kind of interfaces do ALE business processes use?

ALE business processes are integrated processes across distributed systems, requiring interfaces between the systems.

These interfaces have to be stable to enable the communication between different releases and to reduce the impact of release changes within the distributed environment.

In SAP R/3 release 3.0 and 3.1 ALE uses IDocs as interfaces. An IDocs is a data container for transferring messages asynchronously.

They are release independent. Since SAP Release 3.1G BAPIs are a new type of object oriented, stable interfaces that can be called synchronously or asynchronously.

Asynchronous BAPIs use IDocs as data containers. ALE business processes can use BAPIs as well. In the future new ALE business processes will use BAPIs as interfaces. But the existing IDocs will still be supported.

In time, BAPIs will be created with similar functionality to existing IDoc interfaces.

9. Why does SAP uses 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.

10. What is the relationship between ALE and middleware?

For distributed business processes many different services are required. Most of these services are offered by SAP. For some of these services you can also use products that are provided by SAP's complementary software partners or by other companies:

The communication service for doing the pure communication is usually done via Remote Function Call (RFC).

RFC is provided by SAP for most platforms both for synchronous and asynchronous communication. There are other messaging systems for the communication service available as well, like IBM's MQSeries.

However, the communication between SAP and the messaging system is still done via RFC.

For the serialization of asynchronous communication the RFC provides little functionality at the moment.

The serialization has to be checked by the application. ALE offers some support to do these checks.

The serialization of the RFC communication will be improved in the future. Serialization services are provided by some of the existing messaging systems, but even they can not guaranty a 100% serialization of the communication, since they use RFC for the connection to SAP.

The monitoring and error handling of the communication is done via services provided by the RFC and ALE. If messaging systems are used for the communication they also offer some monitoring and error handling functionality.

If a non-SAP system is involved in the ALE business scenario and this system does not understand SAP's BAPI or IDoc interfaces, the data has to be mapped to any interface structure that this system offers.

For this mapping SAP does not provide a service but it certifies mapping tools from software partners. These tools are called ALE translator. The most known product in this area is probably Mercator from TSI International Software. The same kind of mapping can also be done by 'EDI converters'.

Another type of middleware products offer process ware. This is mainly a combination of the communication service, the mapping service and a set of rules for the mapping. Some ALE translator can be used for this as well.

Receiver determination is one of the ALE services (see above). Parts of this service can also be provided by some of the messaging systems, but you cannot use these systems without using ALE receiver determination.

For the other ALE services like application monitoring, application error handling, semantic synchronization and business process harmonization, there are no middleware products available as a replacement of ALE.

ALE is open for the use of middleware products for the distribution, but in most cases the additional middleware is not necessary.

In a communication between different SAP systems usually the use of additional middleware makes no sense at all.

For the communication between SAP and non-SAP systems there might be some benefits, especially if the middleware is used at the company already. The only middleware tool that is really required if the non-SAP system does not understand BAPIs or IDocs is an ALE translator.

11. Performance and scalability?

The performance of ALE business processes depends on many factors (type of business process, number of messages, activities running on the distributed systems, hardware, and so on).

To obtain detailed information about the performance a sizing procedure is required.

The sizing procedure for SAP systems linked via ALE can be divided into two independent steps. In the first step only the activities within one system must be taken into account, in the second step the additional load created by the communication between the systems has to be determined.

The total processing capacity (CPU, main memory, disk space and network bandwidth) needed for each individual SAP system can be calculated as the sum of the two steps of the sizing procedure.

The reason for choosing this simplified sizing model is the following. The resource consumption of a business transaction depends only little on the fact whether the transaction was executed by an online user, a batch job or an interface program processing an IDoc.

This is essentially because the same activities like consistency checks or business functions have to be performed in any case.

Of course the error handling for online users is different from the error handling in batch processing. On the other hand, for batch jobs or interface programs additional protocols have to be written to ensure restartability.

The first step of the sizing procedure is therefore either a user or a throughput based sizing for each SAP system. Thus the same input data is required and the same procedures and models have to be applied as in the standard sizing methodology for a single SAP system.

For the second sizing step - calculating the impact of the data transfer between the ALE linked systems - it is essential to know how many messages of a certain type will be exchanged between the different systems per time interval.

In the receiving system these messages will create additional objects or changes to existing objects, this can be taken into account by a throughput based sizing and has to be added to the numbers calculated for this SAP system in the first sizing step.

The overhead created in the sending system is in most cases less than 10% and can therefore be neglected.

This is due to the fact that normally messages are not sent immediately but bundled to reduce the communication overhead.

Measurements and experience show that the additional network bandwidth needed by ALE in a LAN scenario is much smaller than the network traffic between application and database server because of data compression; for WAN scenarios, however, the size and amount of the IDocs transferred has to be taken into account.

The same sizing considerations are valid for SAP systems connected to non-SAP systems, too.