Linking Tiers with Remote OLE

Divide et impera (divide and rule) -- splitting applications into three parts -- is the state of the art in client/server technology. Modern client/server applications, such as SAP's R/3, use a Presentation Layer (for realizing the user interface) and a Database Layer (for storing persistent data), which are held together by a Business Logic Layer. For performance or maintenance reasons, the different layers can be implemented on distributed systems in a network.

To a programmer, the problem is not whether to split the application, but to choose a distribution technology that allows the parts to communicate over a wide range of networks and OSes. Remote procedure calls (RPCs), Common Object Request Broker Architecture (CORBA), and IBM's Distributed System Object Model (DSOM) are possible solutions. With Visual Basic 4.0 (VB 4) Professional Edition, Microsoft has offered yet another option: Remote OLE.

Remote OLE allows OLE servers and clients to be distributed over a Windows-based network. Instead of invoking OLE server methods on a local machine, the OLE client sends OLE requests over the network to a remote OLE server. Siemens Nixdorf chose Microsoft's Remote OLE as the primary communications technology for distributed, three-tier, client/server applications. Therefore, applications built with ComUnity OT Framework are implemented as VB 4 OLE servers, and thus they can be distributed fairly easily via Remote OLE.

The only catch to this elegant Remote OLE solution is its incompatibility with non-Windows environments.

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Three Tiers for ComUnity

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Implementing ComUnity applications as OLE servers lets them communicate over a network.