Specifications

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Scope
A primary goal for OPC is to deliver specifications to the industry as quickly as possible.
With this in mind, the scope of the first document releases is limited to areas common to all
vendors. Additional functionality will be defined in future releases. Therefore, the first
releases focus on
• Online DataAccess, i.e., the efficient reading and writing of data between an
application and a process control device flexibly and efficiently;
• Alarm and Event Handling, i.e., the mechanisms for OPC Clients to be notified of
the occurrence of specified events and alarm conditions, and
• Historical Data Access, i.e., the reading, processing and editing of data of a
historian engine.
Functionality such as security, batch and historical alarm and event data access belong to
the features which are addressed in subsequent releases. The architecture of OPC leverages
the advantages of the COM interface, which provides a convenient mechanism to extend
the functionality of OPC.
Other goals for the design of OPC were as follows:
• simple to implement
• flexible to accommodate multiple vendor needs
• provide a high level of functionality
• allow for efficient operation
The specifications include the following:
1. A set of custom COM interfaces for use by client and server writers.
2. References to a set of OLE Automation interfaces to support clients developed with higher level
business applications such as Excel, Visual Basic, etc.
The architecture is intended to utilize the Microsoft distributed OLE technology (DCOM) to facilitate clients
interfacing to remote servers.
References
Kraig Brockschmidt ,Inside OLE, Second Edition, Microsoft Press, Redmond, WA, 1995.
Microsoft COM Specification, version 0.9, 10/24/95 (available from Microsoft’s FTP site).
OLE Automation Programming Reference
, Microsoft Press, Redmond, WA, 1996.
OLE 2 Programming Reference, Vol.
1, Microsoft Press, Redmond, WA, 1994.
The OPC Data Access Custom Specification 1.0A, OPC Foundation 1997.
The OPC Data Access Custom Specification 2.0, OPC Foundation 1998.
The OPC Data Access Automation Specification 2.0, OPC Foundation 1998.
The OPC Alarm and Event Access Specification 1.0, OPC Foundation 1998.
The OPC Historical Data Access Specification 1.0, OPC Foundation 1998.
OPC Fundamentals
OPC is based on Microsoft’s OLE/COM technology.
OPC Objects and Interfaces