The OPC Foundation adopted the Express Interface as the
OPC .NET interface that bridges the gap between Microsoft .NET and the world of OPC Classic.
OPC .NET defines a .NET API for the Express Interface.
OPC Foundation members can download sample implementations of servers and clients.
The code includes a wrapper server for OPC DA, HDA, AE and the OPC .NET client API (core client code) with sample client applications.
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The Express Interface (Xi) is a public domain specification that
provides a simple .NET communication interface for OPC Classic servers. Xi is
based on the Windows Communication Foundation (WCF) and defines a
formal interface that combines the semantics of OPC DA, OPC A&E, and
OPC HDA into a single interface and provides additional support for
historical alarms and events.
The Express Interface is the result of a collaboration among several
OPC vendor companies and was developed to allow client applications
to easily use .NET to access existing OPC Classic servers.
The use of WCF allows for simple implementations of Express
Interface (Xi) servers and clients. The Windows
Communication Foundation handles all communication aspects
with a wide range options for local and remote connections
and is available on all .NET platforms including the .NET
Compact Framework and Silverlight.
WCF provides a high level of security through built-in
authentication, authorization and data encryption. It also
simplifies access through firewalls.
Additional security features have been built into the
Express Interface to enable secure server access with high
The Xi specification and
server reference base code are
available under the Express Interface