All of the Specifications of OPC are depend on the model of OPC Client/Server. The Client/Server explains the correlation between 2 applications of computer in which one application: The OPC client is making a service request from another application while the OPC Server is fulfills the request. Although the model of OPC Client/Server can be applied in the single computer, when applied in a network it supplies a modular and versatile infrastructure that provides scalability, interoperability, and flexibility. This model is dissimilar from other general distributed architectures for example Primary/Secondary or Master/Slave and peer-to-peer networks.
In the model of Master/Slave (or Primary/Secondary). The application Master manages one or more applications Slaves. Once the relationship of Master/Slave is recognized, the control direction is always from the master to the Slave. The peer-to-peer is a model of communication in which every party has the similar capabilities and moreover party can start a session of communication.
What is an OPC Server and what is the function? An OPC Server is a software application, which has already written to one of the Specifications of OPC. A Server of OPC will take action to asks for, and give data to one or additional OPC Clients in a standard and consistent method. The submissive OPC Client can interface with and ask for data from any submissive OPC Server, despite of the vendor, or the fundamental system supplying the data. The OPC Clients/Server’s original audience was the industrial Process Automation, to supply a typical interface to devices industry, for example a SCADA, PLC, HMI, DCS, DAS or RTU. Because require an interface standard to get data from a system is not exclusive to this manufacturing, OPC Servers are currently accessible for limitless other systems counting relational databases, historians, scanners of RFID, systems file, applications of enterprise, practice devices, systems of building control, networks IT, etc.
The primary Specifications of OPC , OPC DA (OPC Data Access), OPC A&E (OPC Alarms & Events) and OPC HDA (OPC Historical Data Access) are depend on Microsoft COM and DCOM which is also depend on the model of Client/Server. From the point of view programmatic, the OPC Client terms and COM Client, and COM Server and OPC Server can be applied exchangeable. Each COM Client/Server is also an OPC Client/Server. The OPC Server gives a standard interfaces set, methods and properties acquire information on what data is accessible, and data read and write in a standard method.