Winning the battle for interoperability

In a special-to-the-web article for OPC Connection, OPC specialist Eric Murphy presents his thoughts on what it will take to achieve the mission of true interoperability.

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Eric MurphyBy Eric Murphy, ControlGlobal.com Columnist

END USERS who purchase OPC-compliant products expect 24/7 reliability, full data information integrity and validated, secure interoperability. The product should seamlessly integrate with existing architecture. However, achieving interoperability of some products is more like a running skirmish against hostile opposition -- painful and costly. Getting all sides to comply with the rules and best practices of interoperability can be an uphill battle at times. To combat the problem, the OPC Foundation has created the OPC Enhanced Certification Program.

The clear message from users was they should not need to validate interoperability between vendors. As an industry standard, OPC products should work together seamlessly, securely and reliably. So, when the status quo isn’t sufficient and you foresee marauding forces gathering on the rise, what do you do? Form a battle plan, strengthen the defenses, check the armaments and rally the troops. Achieving the mission on true interoperability takes no less effort. Paul Hunkar, Consultant Engineer with ABB, in his role as the OPC Foundation Managing Director of Certification is the one tasked with leading the charge. "The OPC Foundation is committed to providing the support requested by our end-users and vendors to improve the quality of OPC Products." says Hunkar. "The Compliance Committee, composed of end users, vendors and system integrators, has spent significant time and resources improving the processes available to vendors to improve the quality of their products”

The Battle Plan
A good commander will tell you any battle plan relies on good reconnaissance, so existing OPC vendors and end users were surveyed to determine what was working with the existing compliance procedures, and to identify possible chinks in the armor. The key observations included: 

  • current compliance efforts lacked visibility 
  • it was not easy to identify OPC product certification levels 
  • there was a demand for independent testing facilities and improved testing tools

The OPC Foundation currently provides workshops and automated test tools to help facilitate interoperability. Although these efforts are effective to a certain degree, it was deemed additional improvements where needed to ensure the delivery of quality certified products that exceeded the expectations of the end-user community.

Initial Tactics
The OPC Product Certification section of the Foundation website has been re-designed to make it easier to find OPC-certified applications. Each product has a 'Certification Test Status' associated with each specification that it supports. In addition, each product has an overall test status, which is a composite of the individual specification test statuses. Using various product search options, users can easily determine which OPC products have been fully or partially tested, previously tested against older criteria, recently workshopped, or have never been tested at all.

Another useful status is the ‘Similar Product Tested’ category, which is intended for OPC products that have been built on a common core framework. Since a single framework may represent hundreds of different OPC servers, it would be impractical for vendors to individually certify each OPC server with each new testing tool release or workshop event.

In addition to improving the OPC Foundation website, the Compliance Committee has replaced the existing ‘OPC Compliance Tested’ logo with two new, revamped logos. The new branding will differentiate between OPC products that have been self-tested by vendors using the OPC Foundation-supplied test tools, and those that have been certified by independent third-party testing facilities. This is another important step towards improving the visibility and identification of certified OPC products.

Quartermaster’s Stores
The OPC Foundation has several applications in their testing arsenal. Since OPC products are client-server based, and may support multiple OPC specifications, different testing tools and approaches are needed. For OPC Servers, the OPC Foundation provides a standard software application called the Compliance Test Tool (CTT), which supports the various OPC specifications. Members can download the CTT from the Foundation website and run the tests at their site. The tool generates an encrypted file which is forwarded to OPC Foundation, who then publishes the results on the OPC Product Certification section of the website.

Testing OPC clients is more challenging, since many client applications require only a subset of the full functionality provided by an OPC server. There can also be tremendous variation in how an OPC client may be incorporated into other software applications. The OPC Foundation meets this challenge by offering interoperability testing. This is a process where members attend an annual event and test the OPC client applications against the OPC servers supplied by other members. These events are called interoperability workshops and occur each year in Europe, North America and Japan. The interoperability test process requires that OPC vendors run a series of standard tests for each combination of an OPC client and an OPC server product. The results of these tests are collected and displayed on the OPC Foundation website as part of the overall Certification Test Status.

In spite of the variations of OPC clients available, there is a core set of interfaces and functionality that users have come to expect from all clients to improve interoperability. To ensure these tests are covered by the interoperability workshops, the OPC Foundation has recently developed a standardized OPC client test application called the OPC Analyzer. The tool not only logs all interaction between the OPC client and server, it also has a scripting capability that allows testers to generate error conditions or unexpected behavior in order to test the robustness of the OPC clients. This tool, along with network interrupt testing, allows vendors to determine how their products behave in simulated real world scenarios.

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