Three-Tier Computing Architecture

In three-tier computing, application logic is held in an application server, such as Sybase EAServer, which sits between the resource manager and the client applications. In many situations, a single application server may access multiple resource managers. In the Internet case, client applications are browser-based, and the application server is generally a web server extension.

Sybase EAServer stores application logic in the form of components, and makes these components available to client applications. The components may be PowerBuilder® components, JavaBeans, or COM components.

For more information, see your Sybase EAServer documentation.

• Distributed Transactions in Three-Tier Computing
  When client applications or application servers work with a single transaction processing database, such as SAP Sybase IQ, there is no need for transaction logic outside the database itself, but when working with multiple resource managers, transaction control must span the resources involved in the transaction. Application servers provide transaction logic to their client applications—guaranteeing that sets of operations are executed atomically.
• The Vocabulary of Distributed Transactions
  This section assumes some familiarity with distributed transactions. For information, see your transaction server documentation. This section describes some commonly used terms.
• How Application Servers Use DTC
  Sybase EAServer and Microsoft Transaction Server are both component servers. The application logic is held in the form of components, and made available to client applications.
• Distributed Transaction Architecture
  The following diagram illustrates the architecture of distributed transactions. In this case, the resource manager proxy is either ADO.NET, OLE DB, or ODBC.