OPC .NET 3.0 (formerly known as OPC Express Interface (Xi))
Express Interface - OPC .NET 3.0 (Xi) - is a new .NET specification created by a group of automation vendors. This activity originally took place outside the control of OPC Foundation. The OPC .NET 3.0 specification is based on WCF (Windows Communication Foundation) and MMS (Manufacturing Messaging Service), and is backward compatible with OPC DA, AE and HDA. In essence, OPC .NET 3.0 solves the same problem as the original OPC specifications, but using Microsoft's current technology backplane - .NET, in place of the original COM.
Working outside the auspices of OPC Foundation allowed the OPC .NET 3.0 member companies to proceed quickly. Adoption could also be relatively swift, being unshackled from the restrictions placed by OPC Foundation on distribution of its own specifications and code.
According to the OPC .NET 3.0 website at launch, these vendor companies were initially responsible for the OPC .NET 3.0 specification and sample code:
OPC Foundation subsequently adopted OPC .NET 3.0 into the OPC portfolio, after which it became known as OPC Xi. The OPC .NET 3.0 specification remains freely available.
The OPC .NET 3.0 specification and server reference code are freely available to download from the Express Interface site or OPC Foundation. Other downloads, including clients, wrappers and discovery servers are available only to OPC Foundation members.
These downloads are now fully released at version 1.0.
In addition to the OPC .NET 3.0 reference code, the Express Interface site has a number of sample applications implemented by Advosol, including a test client, simulation server and configuration utility.
Emerson has been the most visible early supporter of OPC .NET 3.0, and is understood to be a major contributor to the deliverables. Emerson announced OPC .NET 3.0 support for their DeltaV range in October 2009.
An OPC .NET 3.0 Technical Overview presentation is available from Emerson via Slideshare.
Advosol is another prominent supporter of OPC .NET 3.0, and is currently responsible for the Express Interface website. In addition, Advosol has made available a number of Internet-facing OPC .NET 3.0 demo servers, and has announced a range of OPC .NET 3.0 components and free tools for developers.
The OPC .NET 3.0 site has a growing list of vendor products.
The OPC .NET 3.0 site has a page comparing the Express Interface with OPC UA and classic OPC specifications. This page points out that OPC .NET 3.0 is backward compatible with OPC DA, AE and HDA.
In late October 2009, OPC Foundation President Tom Burke announced that OPC Foundation would work towards adopting OPC .NET 3.0 as an OPC specification. In the short term, this mark of approval may make OPC .NET 3.0 more acceptable to existing OPC users. However, uptake of recent OPC specifications has undoubtedly been hit by OPC Foundation's policy of restricting access to key deliverables. It would be most unfortunate if the OPC .NET 3.0 group had to sacrifice its pragmatic and open approach to satisfy OPC Foundation, and this would surely limit uptake in the longer term.
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