Introducing the Application Server

The DSM system architecture is based upon a three-tier client/server architecture where an intermediate server is added to the traditional client/server environment. In the DSM system, the Application Server program fulfills the role of the intermediate server and handles the following aspects of the system:

Communications between the DSM client applications and the database server—The inclusion of the Application Server eliminates the need for each DSM client application to be configured for the different database server applications currently available; all direct communication and connections are handled between the database server and the Application Server, rather than between the DSM client and the database server. In addition, because the Application Server has its own processing capabilities, it can assist the DSM client applications in storing and retrieving information on the back-end database.

System licensing—The Application Server provides a specific number of concurrent user sessions in accordance with the active license limits.

Automated upgrading—It is possible to configure the Application Server to provide automated upgrading of the DSM client applications when they attempt to connect to the database.

The Application Server connects to and communicate with the DSM client applications through TCP/IP ports.

Just as a port is needed for the client applications to connect to the Application Server, there must also be a method for connecting the Application Server to the back-end database. The Application Server accomplishes this by creating Database Links that use Open Database Connectivity (ODBC) Data Sources to point to the different databases that might reside on the database engine. For example, the database engine may have multiple system databases: the live company database, the included sample database, a training database, etc. The Application Server provides Database Links that allow client access (through the Data Source) to each of these individual databases. Each database to which you want to provide access will have its own Database Link defined within the Application Server. Each Database Link will in turn have its own Data Source defined to link to the database.

Figure: Communication Process. Client applications communicate through ports, database links, and ODBC data sources to connect to system databases residing on the back-end database server.

The Application Server program is composed of two components: the Application Server service program and the shell program. During installation, the Application Server service program becomes integrated with the Windows Service Control Manager where it can be started and stopped like any other service. Optionally, the Application Server service program can be set to start automatically each time the Windows Server operating system starts (this is strongly recommended to ensure that the Application Server is always active and running). The Application Server Shell program, used mainly for configuring the Application Server, can also be used to manually start and stop the Application Server.