Technology Mapping

Overview

When considering developing applications it soon comes to the question which technology to use for the implementation. There are often many different technology options from which one has to be selected. In some cases it is preferable to apply a matured technology and in other cases innovation is more important. However, when developing a standard, the technology question is not easy to answer if you intend to satisfy everyone in the community. For some people performance and reliability are more important than security, for others this is vice-versa. Another issue that has to be considered for answering the technology question is what happens when a technology retires? Technologies are provided and maintained for certain platforms like operating systems. When new versions of such platforms are provided then sometimes older technologies are replaced by newer ones. The backward compatibility is thereby not always given!

In order to be open for future technologies and to provide certain interoperabi?lity between OPC UA products the working group decided to define services (see Chap. 5) and concepts in an abstract manner and to specify a technological mapping for implementation. The specified mappings address three tasks necessary for exchanging data between OPC UA applications: data encoding, securing the communication, and transporting the data. This is illustrated in Fig. 6.1. OPC UA applications in general can be separated into several functional layers. There are layers for the application logic, for accessing other components (i.e., interfaces) and there are several layers responsible for encoding, security, and transport which can be composed to a so-called stack. Stacks are mostly generic components separated from the real application since they can be reused by many other applications. Reference [UA Part 6] defines for each of the stack’s layer two technologies that can be used for implementation. However, technology evolves and additional technology mappings might be added in the future. In order to develop an OPC UA compliant product (see Chap. 12) at least one of the specified technologies for each layer has to be implemented.