OPC Data Access
group of client–server standards
The OPC Data Access Specification is the first of a group of specifications known as the OPC Classic Specifications.
OPC Data Access is a group of client–server standards that provides specifications for communicating real-time data from data acquisition devices such as PLCs to display and interface devices like Human–Machine Interfaces (HMI), SCADA systems and also ERP/MES systems. The specifications focus on the continuous communication of data.
The OPC Data Access specification is also known as OPC DA. OPC DA deals only with real-time data and not historical data (for historical data you need to use OPC Historical Data Access, or OPC HDA) or events (for Alarms and Events you need to use OPC Alarms and Events, or OPC AE). There are three attributes associated with OPC DA data. These are
a value,
the quality of the value, and
a timestamp.
The OPC DA specification states that these three attributes have to be returned to an OPC client making a request. Therefore, if the data source is not capable of providing a timestamp, for example, the OPC DA server must create a timestamp.
The OPC Classic specifications are based on the Microsoft COM technology and define a C/C++ interface. A standard Automation wrapper interface is also defined for access from Visual Basic, Delphi and other automation-enabled languages.
Begin with the source’s own compact description: “OPC Data Access” is group of client–server standards. The dossier treats that line as a proposition to test through Data, Access and group, not as a finished interpretation.
Why this record matters
The phrase “group of client–server standards” supplies a clear boundary for inquiry. It also exposes the unanswered questions: who defined that boundary, when it became stable and which sources sit outside it.
The citation trail is more important than the brevity of the summary: it shows where individual claims can be examined in context. The source revision retrieved here is dated Oct 16, 2025. The linked authority identifier is Q7072811. None of the 0 selected statements returned an explicit reference.
The absence of detail may reflect summary conventions rather than a lack of surviving documentation. The lead is largely declarative, so disagreement and counter-evidence require a deliberate search beyond the opening account. Authority statements aid reconciliation but still require their own references, qualifiers and ranks to be checked.
How to read it
Use the entry as an orientation point, then follow its citations and revision history. Names, dates and institutional relationships should be checked against the original record.
- Subject orientation
- Search vocabulary
- Locating named sources
The closest primary source, responsible institution and strongest cited specialist reference.
Three-step research path
- Establish the record: confirm the title “OPC Data Access”, its source revision and the description used here.
- Expand the search: follow OPC Data Access primary sources, OPC Data Access archive and Data research across catalogues and specialist indexes.
- Test the account: compare the strongest cited source with the responsible institution’s current record and note any disagreement.
Questions for further research
- Which source most directly establishes the central claim about “OPC Data Access”?
- Which cited source is closest to the event, object or claim?
- What terminology or title could unlock a more precise catalogue search?
Search terms from this dossier
This entry incorporates text from “OPC Data Access” on English Wikipedia. Contributors are listed in the page history. Text is available under the Creative Commons Attribution-ShareAlike 4.0 License. Selected authority identifiers and statements are retrieved from Wikidata under CC0; their references and qualifiers remain part of the verification path.