OPC Data Access (OPC DA) provides access to real time automation data. Using OPC DA, software applications can retrieve real-time data to enable them to monitor a given process. In that scenario, OPC DA is used for data acquisition. OPC DA can also be used to enable a software application to write data to a control system. This enables OPC DA applications to handle supervisory control. Thus, OPC DA is well suited for Supervisory Control and Data Acquisition (SCADA) scenarios. OPC DA is typically used by almost all process control applications that are used as an HMI, Historian, Advanced Process Control (APC), Maintenance, ERP (Enterprise Resource Planning), Analysis, Optimization, etc.
OPC DA enables the exchange of real-time process data, in other words, the latest values. To get the previous values, applications must use OPC HDA (Historical Data Access). The OPC Foundation is responsible for defining and maintaining the OPC Batch specification.
The OPC Data Access (OPC DA) 3.00 specification published by the OPC Foundation is intended as reference material for developers of OPC compliant Clients and Servers. It is assumed that the reader is familiar with Microsoft OLE/COM technology and the needs of the Process Control industry.
The specification is intended to facilitate development of OPC Servers in C and C++, and of OPC client applications in the language of choice. Therefore, the developer of the respective component is expected to be fluent in the technology required for the specific component.
The deliverables from the OPC Foundation with respect to the OPC Data Access Specification 3.0 include the OPC Specification itself, OPC IDL files (included in this document as Appendices) and the OPC Error header files (included in this document). As a convenience, standard proxy stub DLLs and a standard Data Access Header file for the OPC interfaces generated directly from the IDL will be provided at the OPC Foundation Web Site. OPC Data Access 3.0 sample code is also available from the OPC Foundation Web Site (members only).
Visit the OPC Foundation website to download the OPC Data Access (OPC DA) 3.00 specification.