Specifications

RSLinx – Training Guide B - 9
OPC Alarm&Event Server,
OPC HistoricalData Server.
The Current Client Application Architecture
There are many client applications that have been developed that require data from a
data source and access that data by independently developing “Drivers” for their own
packages.
This leads to the problems that follow:
• Much duplication of effort
Everyone must write a driver for a particular vendor’s hardware.
• Inconsistencies between vendors drivers
Hardware features not supported by all driver developers.
• Support for hardware feature changes
A change in the hardware’s capabilities may break some drivers
• Access Conflicts
Two packages generally cannot access the same device simultaneously since they
each contain independent Drivers.
Hardware manufacturers attempt to resolve these problems by developing drivers, but
are hindered by differences in client protocols. Today they cannot develop an efficient
driver that can be used by all clients.
OLE for Process Control (OPCä) draws a line between hardware providers and
software developers. It provides a mechanism to provide data from a data source and
communicate the data to any client application in a standard way. A vendor can now
develop a reusable, highly optimized server to communicate to the data source, and
maintain the mechanism to access data from the data source/device efficiently.
Providing the server with an OPC interface allows any client to access their devices.
The Custom Application Architecture
A growing number of custom applications are being developed in environments like
Visual Basic (VB), Delphi, Power Builder, etc. OPC must take this trend into account.
Microsoft understands this trend and designed OLE/COM to allow components (written
in C and C++ by experts in a specific domain) to be utilized by a custom program
(written in VB or Delphi for an entirely different domain). Developers will write
software components in C and C++ to encapsulate the intricacies of accessing data from
a device, so that business application developers can write code in VB that requests and
utilizes plant floor data.
The intent of all specifications is to facilitate the development of OPC Servers in C and
C++, and to facilitate development of OPC client applications in the language of choice.