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New Spec Aimed at Web Services in Manufacturing

The OPC XML DA specification opens the way to Internet data transfer and cross-platform interoperability.

Use of Internet-based Web Services in mixed-vendor manufacturing environments becomes a lot easier with the recent release of the OPC XML DA specification (for OLE for Process Control eXtensible Markup Language Data Access). The new specification, released in late August by the OPC Foundation, provides a gateway to the Internet for OPC data to be transferred to and from any OPC-enabled device.

The OPC XML DA specification enables vendors to add OPC support to any device on the factory floor that is capable of supporting a Web service, said an OPC Foundation press release. This facilitates the OPC data exchange protocol for communicating data and information seamlessly and transparently between devices independent of the operating system and networking technology that the specific device employs.

The OPC Foundation is a nonprofit organization comprised of manufacturers and solution providers and is dedicated to interoperability in automation. “Our vision is to proactively support technology trends, to ensure members can build highly integrated and interoperable systems,” said Tom Burke, OPC Foundation president. “Internet-based HMI [human-machine interface] is one possibility opened up by OPC XML DA. Others include Web-enabled field devices and enterprise-wide management systems.”

The OPC XML DA specification is now available complete with sample code for immediate use, Burke said.

Prior to the OPC XML DA specification, OPC required the use of Microsoft Component Object Model/Distributed Component Object Model (COM/DCOM) to provide data access and exchange services between multiple vendor products. However, DCOM cannot pass through firewalls, so communications over the Internet have previously been impossible.

What firewall?

XML is one of the key enabling technologies for achieving global interconnectivity and it has wide support as a standardized way of handling data among systems using a variety of operating systems. Because it is text-based, XML can pass through firewalls. The OPC XML DA specification defines how XML is used by OPC clients and OPC servers, allowing end-users to deploy systems with commercial off-the-shelf products for interoperability across networks.

Definitions for supporting Web Services are also provided, enabling users to make simple application-to-application connections over the Internet. To assist migration, the OPC Foundation has developed an adaptive wrapper that provides Foundation members with an easy way to deploy Web Services on top of existing OPC Data Access 2.x COM-based servers. This means that an estimated 3,000 OPC Data Access servers worldwide could be readily Web-service enabled.

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