View source for Engineering:OPC Data Access

{{Infobox protocol|name=OPC Data Access (OPC DA)|image=|industry=[[Engineering:Operational technology|Operational technology]] and [[Engineering:Information technology|Information technology]]|standard=OPC DA specification|developer=[[Organization:OPC Foundation|OPC Foundation]]|introdate={{Start date and age|1996|08}}|homepage=https://opcfoundation.org/about/opc-technologies/opc-classic/|newer=[[OPC Unified Architecture]]|hardware=[[Software:Windows|Windows]]}}
The '''OPC Data Access''' Specification is the first of a group of [[Specification (technical standard)|specifications]] known as the OPC Classic Specifications.<ref>{{Cite web|url=https://opcfoundation.org/developer-tools/specifications-classic/data-access/|title = Members}}</ref>

OPC Data Access is a group of [[Client–server model|client–server]] standards that provides specifications for communicating real-time data from [[Data acquisition|data acquisition]] devices such as [[Programmable logic controller|PLC]]s to display and interface devices like Human–Machine Interfaces (HMI), [[SCADA]] systems<ref>{{Cite web|url=https://opcfoundation.org/about/what-is-opc/|title = What is OPC?}}</ref> and also [[Enterprise resource planning|ERP]]/[[Manufacturing execution system|MES]] systems.<ref>{{Cite book | url=https://books.google.com/books?id=8Lj8CAAAQBAJ&q=ERP%2FMES%20%22OPC%20DA%22%20OR%20%22OPC%20Data%20Access%22&pg=PA352 |title = Fieldbus Technology: Industrial Network Standards for Real-Time Distributed Control|isbn = 9783662072196|last1 = Mahalik|first1 = Nitaigour P.|date = 2013-03-09| publisher=Springer }}</ref> 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 [[Finance:Quality (business)|quality]] of the value, and
# a [[Physics:Timestamp|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 [[Company:Microsoft|Microsoft]] [[Component Object Model|COM]] technology<ref>{{Cite web|url=https://opcfoundation.org/about/opc-technologies/opc-classic/|title = Classic}}</ref> and define a C/[[C++]] [[Interface (computing)|interface]]. A standard [[OLE Automation|Automation]] [[Wrapper library|wrapper]] interface is also defined for access from [[Visual Basic]], Delphi and other automation-enabled languages.<ref>{{Cite web|url=https://opcfoundation.org/developer-tools/developer-kits-classic/automation-wrapper/|title=Members}}</ref> Several vendors offer .NET toolkits to make the OPC interface accessible in .NET applications.

The newer OPC .NET ([[OPC Xi]]) specification is based on WCF ([[Organization:Windows Communication Foundation|Windows Communication Foundation]]) and defines a .NET interface with the functionality of the OPC Classic specifications OPC DA, OPC HDA and OPC AE (Alarms&Events).<ref>{{cite web |url=https://opcfoundation.org/about/opc-technologies/opc-net-4-0/ |title=.NET 4.0 (WCF) {{!}} OPC Foundation |website=opcfoundation.org |url-status=dead |archive-url=https://web.archive.org/web/20140703074027/https://opcfoundation.org/about/opc-technologies/opc-net-4-0/ |archive-date=2014-07-03}} </ref>

The more recent [[OPC Unified Architecture]] allows the same functionality but offers platform independence and optionally complex information modelling capabilities.<ref>{{Cite web|url=https://opcfoundation.org/about/opc-technologies/opc-ua/|title = Unified Architecture}}</ref>

==See also==
* [[Organization:OPC Foundation|OPC Foundation]]
* [[Distributed Component Object Model]]
* [[OPC Unified Architecture]]

==References==
{{Reflist}}

==External links==
*[http://www.opcconnect.com/ OPC Programmers' Connection]

{{Automation protocols}}

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[[Category:Industrial automation]]

{{Sourceattribution|OPC Data Access}}