Communication between OPC and DCOM

Question

I am trying to understand the relationship between OPC and DCOM. I looked through all four tutorials here , and I think I have a good feeling that OPC, but in one of the lessons (the third is 35 seconds), the narrator claims that OPC is based on DCOM, but I don’t understand how these two really connected. My confusion comes from a question asked by my professor, in which he asked: "How and where will you deploy OPC instead of DCOM and vice versa." His question makes me think that the two are not connected as my studies show. I am not looking for anyone to answer the question asked by my professor, I just want to know the connection between OPC and DCOM, and then I can understand the rest. In particular, I would like to know if: 1.) One is always based on the other 2.) One can always deploy without the other.

Answer 1

As I read this, DCOM / COM / OLE was a substrate on which OPC standards were embedded in windows (which are binding objects defined by interfaces as method groups). In other words, OPC, which consists of an object, interfaces, and methods, may have been built by DCOM, which is a technology in windows that allows you to create them.

Therefore, OPC can be built from other substrates, but I am not knowledgeable enough to know if this was. I suspect yes for non-window based systems.

From here

OPC is an open connection in industrial automation and enterprise systems that support the industry. Interoperability is achieved through the creation and maintenance of open standards. There are currently seven specification standards completed or in development.

In particular:

OPC is a series of standards technical specifications. The first standard (originally called simply the OPC Specification and now referred to as the Access Specification Data) resulted from the collaboration of a number of the world's leading automation providers working in collaboration with Microsoft. Initially based on Microsoft OLE COM (Component Object Model) and DCOM (Distributed Component Object Model) technologies, the specification defined a standard set of objects, interfaces, and methods for use in process control and manufacturing automation applications to facilitate interoperability. COM / DCOM technology provided the foundation for software development. There are currently hundreds of OPC data access to servers and clients.

Answer 2

The original OPC specifications were based on COM - not DCOM. This means that the server can be implemented as a COM server in a process that does not require the use of DCOM. In practice, almost all classic OPC products require DCOM.

In 2003, the OPC Foundation released XML-DA, which provides the same features as OPC DA, but uses XML Web Services instead of DCOM.

Next Generation Technology: Unified OPC (UA) architecture was launched in 2009 and is independent of transport technology. Implementations currently support communication through XML Web Services and UA TCP (a binary protocol defined by the OPC Foundation).

Further information can be found here: opcfoundation.org/ua