New OPC spec links devices via the Net

Exchanging data and information between shopfloor devices from different suppliers should become easier, following the release of a new document by the OPC Foundation. The XML Data Access (XML DA) specification will allow equipment suppliers to add OPC support to any device on the factory floor that can support a Web service.

The new specification will provide a gateway to the Internet for transferring OPC data and information to and from any OPC-enabled device, regardless of its operating system or its networking technology. Potential applications include Internet-based HMIs, Web-enabled field devices and enterprise-wide management systems.

The OPC Foundation is providing a "wrapper" that will allow Web services to be added to the 3,000-plus OPC DA products already on the market.

Before the release of this specification, the only way to exchange data between OPC-based products was to use Microsoft`s COM/DCOM. But DCOM cannot pass through firewalls, so communications over the Internet were impossible.

By using the text-based XML (eXtensible Markup Language), the new specification overcomes this limitation. It defines how XML is used by OPC clients and servers, allowing end-users to achieve interoperability between off-the-shelf commercial products.

Originally, OPC was used mainly to transfer data between Distributed Control Systems and HMIs or Scada. Its capabilities were extended recently with the launch of OPC DX, which allows data to be moved horizontally between control platforms.

"XML DA empowers members to develop far more sophisticated OPC products, communicating data not just between themselves, but globally," says Russ Agrusa, OPC Foundation`s marketing director.

Dick Slansky, a senior analyst with ARC Advisory Group, says that the new specification "ushers in a new era of interoperability," and provides "an extremely significant step towards making Web services for manufacturing a reality".