The OPC .NET (Xi) Express Interface is a Microsoft .NET based interface specification designed for secure and reliable access to real-time and historical process automation system data. Xi provides a standard, .Net based interface for “classic” OPC server functionality, OPC Data Access (DA), OPC Alarms & Events (A&E) and OPC Historical Data Access (HDA) and represents a natural progression of Microsoft communication technology from Microsoft Component Object Model (COM) to .Net.
Xi provides the same functionality as the classic OPC servers while addressing some of the known shortcomings of classic OPC. The classic OPC servers are based on COM communications, which was state of the art when the OPC specifications
were created, but since the introduction of OPC DA in 1996, Microsoft has moved from COM to .Net communications. COM is efficient for local server access but can be difficult to configure for remote server access and problematic for communication through firewalls.
In addition to classic OPC functionality, Xi provides the following features:
- Secure communications. Xi delivers a firewall friendly interface and patented security features to provide secure communications between process automation systems and higher level manufacturing execution systems (MES) and enterprise resources planning (ERP) systems.
- Robust connectivity. Xi increases client connectivity robustness by maintaining the state of the client connection, allowing the
client to reconnect quickly and easily if communications with the server were lost.
- Plug and play. Xi provides automatic server discovery which allows Xi clients to automatically discover and connect to Xi servers.
- One interface for real-time, historical and event data transfer. Xi provides a single interface to read and write real-time process data, subscribe to real-time alarms and events and read and write historical data.
- Based on open, industry standards. Xi is based on Windows Communication Foundation (WCF), the latest communications technology available from Microsoft. Using WCF, a Xi server is able to offer industry standard communication protocols, such as the Transmission Control Protocol (TCP), the Hypertext Transfer Protocol (HTTP) and Secure Hypertext Transfer Protocol (HTTPS).
- Easy to implement. Xi provides .Net client applications a simple .Net interface for easy access to classic OPC servers. Xi client applications can take advantage of new user interface technologies available in Windows Presentation Foundation (WPF).
- Useable on all .NET platforms. .NET platforms such as Silverlight and the Compact Framework don't support DCOM but support s subset of WCF. Xi clients on these platforms can access classic OPC server through Xi converter servers.
- Access data from anywhere. Xi delivers a secure and robust .Net interface that supports interprocess and TCP communications for .Net based Xi clients and a Web service interface for Internet based or non-Microsoft based Xi clients.
- Future proof. As new WCF communication technologies become available, Xi can use these new technologies to provide additional connectivity options.
- Easy migration from classic OPC. Xi products can wrap classic OPC clients and servers to provide a quick and easy migration path from OPC to Xi. Xi is
also network compatible with classic OPC servers and thus may be used in the same system as classic OPC clients and servers.