By Dan Hebert, PE Senior Technical Editor
[This article first appeared in Control in October 2007.]
OPC Unified Architecture (UA) is supposed to standardize and simplify connectivity among all sorts of software applications from embedded software at the field-device level up to ERP systems running on mainframes. Earlier OPC standards have been helpful to some, confusing to others, and, overall, an advance for our industry.
But, even after listening to presentations during an OPC-UA conference this year, reading the literature, and consulting trusted experts, its tough to tell if OPC-UA will live up to its promise.
OPC-UA is complex, built on myriad other not-so-familiar IT technologies. OPC-UA is a service-oriented architecture (SOA) that will facilitate integration of simple and complex information models from applications and devices, says Thomas Burke, OPC Foundations (opc.org) president and executive director.
Thats a mouthful, and all the explanations of OPC-UA that Ive seen, heard, or read assume the audience has an in-depth understanding of SOA. Well, I dont, and I havent found anyone who can explain it in terms I can understand. I wont attempt to regurgitate incomprehensible explanations.
The best that I can do is draw an analogy with Internet server/browser technology.
Ten years ago, I had no idea what this technology was all about and no one could explain it to me in clear terms. Now that Ive used browsers and written pages for a web server, my understanding is adequate, and I know that the technology is here to stay.
I think the same thing will happen with SOA in general and with OPC-UA in particular because I see many similarities between them and Internet server/browser technology.
All the big names in the industry are on board with SOA and OPC-UA, and no one company is seen as their creator, owner or chief proponent. That made Internet server/browser technology a winner, and I think the same can be true for SOA and OPC-UA.
I also think SOA and OPC-UA will be winners because, much like Internet server/browser technology, neither is based on a particular hardware platform or operating system.
Existing OPC standards were designed to address interoperability inside the corporate firewall and were very tied to the Microsoft platform for many good reasons, says Burke. OPC-UA is designed for platform independence. This lets users integrate devices and applications on a Microsoft or a non-Microsoft platform.
OPC-UA essentially builds on existing OPC standards but extends the functionality to facilitate deployment on embedded devices as well as enterprise platforms.
A third reason to believe in OPC-UA is OPC Foundations standardization and testing methods. OPC-UA seeks to ensure interoperability and reliability in several ways, explains Nathan Pocock, chief software architect at Software Toolbox. First, the OPC Foundation is writing the code intended to be the underlying framework all UA software is based on. Second, the application programming interface will be exhaustively tested before its released. Finally, the updated OPC certification program will recognize vendors that test their software for interoperability and compliance.
How is OPC-UA different from other OPC standards? OPC-UA is designed to integrate all existing OPC standards, continues Pocock. In the past, OPC clients had to implement specific OPC interfaces to allow interoperability with data access, alarms and events, and historical data access servers.
Each of these existing standards addressed a specific problem, but didnt interoperate or even consider the existence of the other OPC standards. UA changes the game and fixes this problem because the UA framework will allow seamless integration between components.
OPC-UA might be a winner, but it wont be easy to learn or implement.
As with any new technology, end users will face an implementation learning curve, says Eric Murphy, advanced architecture system design engineer with MatrikonOPC (matrikonopc.com), in Edmonton, Alberta. OPC-UA leverages service-based architectures that might be more familiar to IT professionals than to process control engineers.