Compatibility and Interoperability of an OPC server on the IGUANA gateway

Compatibility and interoperability between different OPC XML-DA implementations basically depends on the following two issues:

1. Compatibility of SOAP Frameworks:

Information in OPC XML-DA is exchanged via SOAP messages, which are constructed with a SOAP framework. To maintain interoperability, these frameworks must be compatible. The OPC specification additionally provides a WSDL document which specifies the format of SOAP messages. The SOAP framework may therefore improve compatibility by validating incoming and outgoing SOAP messages utilizing the constraints in the WSDL documents.

2. Accuracy of the OPC XML-DA specification:

To ensure interoperability, a specification must be very accurate and precise. If it is loose or unclear in some parts, it may lead to custom interpretations, leading to incompatible implementations of the standard.

Testing for compatibility and interoperability between different OPC implementations can basically be done in two ways:

1. Interoperability tests:

In this practical approach, different OPC servers and clients are connected with each other and tested for interoperability. Although such tests provide an interesting overview, reasons for lack of compatibility cannot easily observed as they may either lie in the underlying SOAP framework or in the OPC implementation.

2. Observations during the implementation:

During the implementation, the programmer will have to deal with shortcomings of the SOAP framework, loose definitions in the OPC specifications or other problems which affect the compatibility. These findings can be collected and may prove valuable information for estimating interoperability.

This analysis focuses on the observations during the implementation. Moreover, practical tests will be done, although they are limited due to lack of available OPC implementations.