Question

I am trying to grasp the link between OPC and DCOM. I have watched all four of the tutorials here and I think I have a good feeling for what OPC is, but in one of the tutorials (the third one 35 seconds in) the narrator states that OPC is based on DCOM, but I do not understand how the two are really linked. My confusion comes from a question my professor posed in which he asked “How and where would you deploy OPC instead of DCOM and vice-versa.” His question makes it seem like the two are not as linked as my research suggests. I’m not looking for anyone to answer the question my professor asked, I just want to know the relation between OPC and DCOM, then I can figure the rest out. Specifically I would like to know if: 1.) One is always based on the other 2.) One can always be deployed without the other.

Answer 1

The way I read this is that DCOM/COM/OLE was the substrate upon which OPC standards (which are intercommunicating objects defined by interfaces as groups of methods) were built in windows. In other words OPC which consists of object, interfaces and methods can be and has been built out a DCOM which is a technology on windows that allows the creation of these.

Hence OPC could be built out of other substrates, but I’m not familiar enough with to know if it has been. I’d suspect yes for non windows based systems.

From here

OPC is open connectivity in industrial
automation and the enterprise systems
that support industry.
Interoperability is assured through
the creation and maintenance of open
standards specifications. There are
currently seven standards
specifications completed or in
development.

Specifically:

OPC is a series of standards
specifications. The first standard
(originally called simply the OPC
Specification and now called the Data
Access Specification) resulted from
the collaboration of a number of
leading worldwide automation suppliers
working in cooperation with Microsoft.
Originally based on Microsoft’s 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. The COM/DCOM
technologies provided the framework
for software products to be developed.
There are now hundreds of OPC Data
Access servers and clients.