What is the role of interfaces IOPCServer, IOPCDataItem, IOPCGroup in OPC ( OLE for process control)

Question

I am currently new in OPC ( OLE for process control). I want to know about the interfaces IOPCServer, IOPCDataItem, IOPCGroup interfaces in the OPC. What are they used for & what is their role in terms of OPC Client & OPC Server & what methods & properties these interfaces conatins ? Can you provide me the answer for the above questions or can you provide me the link through which I can get the knowledge of the above topics ?

Answer 1

You're probably talking about the OPC DA (Data Access) interfaces. You would have to know which version of OPC DA you're targeting (most likely versions are 2.05a and 3.0).

The interface specifications are served by OPC Foundation, and they require a paid membership to download the specifications. See: http://www.opcfoundation.org/Downloads.aspx?CM=1&CN=KEY&CI=274 ; or you might be able to catch a glimpse of the specs for free online, search around, for example see: http://www.doc88.com/p-67617868554.html

Download the OPC DA redistributable package from OPC Foundation (this is free even for non-members). Then you can see the full API definitions in the included IDL files.

Anyway, IOPCServer is the "root" interface through which the client connects and gets the references to all the other objects. Practically it has the semantics of a connection-type object. Its methods provide some basic services (e.g. server state management), as well browsing all the served items and their properties.

IOPCGroup provides a way of grouping data items for collective reads and writes. A group is a collection if items which are read with the same cycle, and have the same deadbands. It contains methods for adding/removing items and reading them synchronously or asynchronously.

IOPCDataItem I have never seen (in DA 2.05 or DA 3.0). Could you be referring to IOPCItemIO, which is the way to read/write items directly without creating groups (in 3.0 only)?