OPC Express Interface - Xi

Introduction Downloads Xi Vendors Express Interface and OPC

Introduction

Express Interface - 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 Xi 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, Xi 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 Xi 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 Xi website at launch, these vendor companies were initially responsible for the Xi specification and sample code:

• Advosol
• Emerson Process Management
• Honeywell
• Iconics
• InduSoft
• Matrikon
• MYNAH Technologies
• Mobiform
• OSIsoft
• Smar

OPC Foundation subsequently adopted Xi into the OPC portfolio, after which it became known as OPC Xi. The Xi specification remains freely available.

Downloads

The Xi 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 were at Release Candidate status at the time of writing (2010-03-04). The final release is scheduled for 2010-03-15.

Xi Vendors

Emerson has been the most visible early supporter of Xi, and is understood to be a major contributor to the deliverables. Emerson announced Xi support for their DeltaV range in October 2009.

An Xi Technical Overview presentation is available from Emerson via Slideshare.

Advosol is another prominent supporter of Xi, and is currently responsible for the Express Interface website. In addition, Advosol has made available a number of Internet-facing Xi demo servers.

The Xi site has a growing list of vendor products.

Express Interface and OPC

The Xi site has a page comparing the Express Interface with OPC UA and classic OPC specifications. This page points out that Xi 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 Xi as an OPC specification. In the short term, this mark of approval may make Xi 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 Xi group had to sacrifice its pragmatic and open approach to satisfy OPC Foundation, and this would surely limit uptake in the longer term.