SAP R3 - as was commonly called before the advent of SAP ECC - refers to a 3-tier architecture from the Software-oriented view and is still an integral part of various SAP solutions including SAP ERP...

In the beginning of 1970s, when SAP started business, there were big computers and only big business organizations or some research labs could afford them. Everything including database, application software and user interface was on this one big machine. SAP was a start-up company and had introduced its Finanical Accounting software. It is called R/1 now as SAP picked this nomenclature down the line. 'R' stood for Real Time Data Processing - which was (and is) at the heart of the SAP software.

With the development in computing technology, the processing power improved, the new software languages arrived and it was possible for several users to work on one mainframe computer through terminals. SAP launched R/2 in 1982 and it separated the user interface from the application software and database both of which still resided on one mainframe computer. SAP R/2 was successful during 1980s and early 1990s as it was popular with several European companies who needed business software with multi-currency and multi-language capabilities.

In the year 1992, SAP launched SAP R/3 based on client-server architecture and proved out to be an immensely successful product.

When the Personal Computers arrived on the scene in 1990s, it was a giant leap from terminals on Mainframes - the kind of revolution we are witnessing now with mobile and other hand-held devices.The terminals on the mainframe were devoid of any processing power and just provided an interface to the user to work on the mainframe computer (server). PCs in contrast had computing power of their own and could function stand-alone similar to a mainframe computer. When on network, the PCs could supplement the processing power of its server.

This feature allowed SAP to move some server-side processing to these machines on the network using the client/server architecture.

As you have seen from the discussion above, SAP software has undergone significant transformation. SAP R/3 as a product was replaced by SAP ERP during the course of its history and now by SAP ECC. But the 3-tier architecture of SAP R/3 is still an integral part of SAP ECC and other SAP solutions like CRM, SCM, etc. Actually ECC offers what R/3 could offer and more. From this point of view, the discussion on SAP R3 is still relevant and helps to understand the basic concepts.

As we discussed above, 'R' in 'R/3' stands for Real-time data processing and the number 3 denotes its 3-tier architecture – Database layer, Application layer and Presentation layer. You can understand them as three software components. Together they make SAP Basis system – the technological foundation of SAP ERP applications.

Database Layer

The database layer consists of the database system - the database and DBMS (Data Base Management System). It stores the data – business data, system tables, SAP programs – all conceivable data which may be present in an SAP system. Till 2010, SAP did not have database system of its own. It came from different vendors. A few database systems which you may find with SAP in different implementations are Oracle, Microsoft SQL Server, IBM DB/2, Siebel, Sybase, etc.

SAP acquired Sybase in 2010 which brought Sybase database systems to SAP product portfolio. Since SAP and Sybase are the same company now, SAP naturally recommends Sybase.

Application Layer

Application layer is where SAP software runs. It consists of at least one application server (one computer system) which offer the services to users. One of the salient features of the application layer is Scalability. As the organization grows larger and more users are added, more application servers can be added to the system landscape. This adjustment of system capability with the business growth is called scalability. It aims to meet the increased business needs.

If there are more than one application servers, each server may not offer all the services and may be distributed among them with overlapping. In this scenario, there is one Message server responsible for communication among application servers. The message server also contains information about these servers and load balancing among them.

Presentation Layer

This is the software component for graphic user interface. It is called SAPgui and is the interface between an SAP system and the user. It gets the user input, sends it to application server for processing, receives data, formats and output it. The presentation layer resides on a user’s PC or laptop and uses its resources like RAM, processor, monitor, etc. An SAPgui session on the presentation server (desktop or laptop) is linked to a terminal session on the application server. The following figure shows an SAP user session using SAPGui :

Implementation of 3-tiers

The 3-tier architecture may be implemented in different ways. The 3 layers can be implemented on different servers. The database and application layers may reside on the same server, for example. Even one host can accommodate more than one instances of application server.

Even all the 3 tiers can exist on one system. This system can be a PC or laptop of modern configuration and not necessarily high end server. This system has a database system (Database + DBMS) and stores the data in this database. It also works as the application server to perform task, process and execute transactions. It is presentation server too. Only one user can work at one time. Such a configuration is useless for companies but may be suitable for demonstration purposes.

Advantages of 3-tier architecture

The central database is heavily loaded as all the data is here. All users and all types of data processing use it. So it is best to keep it separate from application server and this separation of Application layer from Database layer leads to improved performance of both.

This results in one more advantage: Scalability, which means that if the number of users have to increase as a result of business growth, it can be achieved by installing one or more application servers.

In the same way, the separation of application layer from presentation layer also distributes load on the system. Presentation server hosts the GUI software which deals with data formatting, screen output, integration with other desktop applications like Microsoft Excel, Word, etc and does not involve application server in these tasks which is involved with program execution. SAPgui and presentation layer software components are designed to keep the data flow between them to the minimum.

End Note

With the advancements in the field of web development and its adoption by SAP in technologies like Web Dynpro embracing MVC architecture, the ERP software has gone beyond its 3-tier architecture. SAP R3 is now one of the components in the larger picture.

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