Release 10.1A: OpenEdge Getting Started:
Application and Integration Services

Application services

An application service has both a general and specific definition for an AppServer. In general, an application service is the entire business function provided by an AppServer. An application service also has a specific identity in the form of a name that identifies it to controlling NameServers and connecting clients. An application service name is essentially an arbitrary alias for the AppServer that provides its particular business function. An AppServer instance can register with more than one application service name to identify its function. Because the different application service names registered by an AppServer are simple aliases, a client application can call any remote procedure or user-defined function supported by the AppServer instance no matter what application service name the client uses to connect the AppServer.

Note: For Open Clients and Progress 4GL Web services, the available remote procedures and user-defined functions are limited by a well-defined interface that you specify and generate appropriately for the client type. Therefore, this interface represents a proper subset of the functionality available in the application service. For more information, see OpenEdge Development: Open Client Introduction and Programming .

For example, an AppServer instance that accesses an inventory database with certain 4GL procedures might support an application service named “Inventory.” An AppServer instance that accesses an employees database with certain other 4GL procedures might support an application service named “Employees.” On the other hand, the same AppServer instance might support both the “Inventory” and “Employees” application services.

Assigning application service names

You specify the application service names that an AppServer supports when you configure an AppServer instance. Client applications use the application service names you specify to identify to a NameServer an AppServer instance with which to connect. The NameServer then chooses a particular AppServer instance to connect based on whether it supports the application service specified by the client.

For multiple AppServer instances that support the same application service name, you typically configure all such AppServer instances with functionally identical capabilities. Most important among these common capabilities include using the same 4GL procedure installation and configuration, and assigning the same operating mode to each AppServer instance.

Fault-tolerant and load-balanced AppServer support

When distributing connection requests for fault-tolerant and load-balanced AppServers, the controlling NameServer assumes that all AppServer instances that support the same application service also support the same API. The NameServer does not validate this assumption. You must ensure that the same published API is available on all AppServer instances that register the same application service name with a NameServer. For more information on fault-tolerant and load-balanced AppServers, see the information on AppServer administration in OpenEdge Application Server: Administration . For more information on how OpenEdge manages connection requests for fault-tolerant and load-balanced AppServers, see the information on session models and application services in OpenEdge Application Server: Developing AppServer Applications .

Default service

A client application can connect to an AppServer without specifying an application service. In this case, the NameServer uses whatever AppServer registers itself as the default service. You can specify any AppServer instance as the default service during AppServer configuration. However, Progress Software Corporation recommends that you avoid relying on the default service and provide explicit application service names for all AppServer instances that rely on a controlling NameServer for client connections. For more information on AppServer configuration, see OpenEdge Application Server: Administration .