Editing Open Platform Communications (section)

==History== <!-- or something to say we are not in the Introduction any more -->
The OPC specification was based on the [[Object Linking and Embedding|OLE]], [[Component object model|COM]], and [[Distributed Component Object Model|DCOM]] technologies developed by [[Microsoft Corporation]] for the [[Microsoft Windows]] operating system family. The specification defined a standard set of [[Object (computer science)|object]]s, [[Interface (computer science)|interfaces]] e.g. [[Interface description language|IDL]] and [[Method (computer science)|methods]] for use in process control and manufacturing automation applications to facilitate [[interoperability]]. The most common OPC specification is [[OPC Data Access]], which is used for reading and writing real-time data. When vendors refer to "OPC" generically, they typically mean [[OPC Data Access]] (OPC DA). OPC DA itself has gone through three major revisions since its inception. Versions are backwards compatible, in that a version 3 OPC Server can still be accessed by a version 1 OPC Client, since the specifications add functionality, but still require the older version to be implemented as well. However, a client could be written that does not support the older functions since everything can be done using the newer ones, thus a DA-3-compatible client will not necessarily work with a DA 1.0 Server.

In addition OPC DA specification, the OPC Foundation maintains the [[OPC Historical Data Access]] (HDA) specification. In contrast to the real time data that is accessible with OPC DA, OPC HDA allows access and retrieval of archived data.

The OPC Alarms and Events specification is maintained by the OPC Foundation, and defines the exchange of alarm and event type message information, as well as variable states and state management.<ref>[https://opcfoundation.org/developer-tools/specifications-classic/alarms-and-events/ OPC A&E specification]</ref>
By 2002, the specification was compared to [[Fieldbus]] and other previous standards.<ref>{{Cite book |title= OPC (OLE for process control) specification and its developments August 5, 2002 |work= Proceedings of the 41st SICE Annual Conference |author= Li Zheng and H. Nakagawa |date= 2002 |volume= 2 |pages= 917–920 |doi= 10.1109/SICE.2002.1195286 |publisher= IEEE |isbn= 0-7803-7631-5 |s2cid= 114855720 }}</ref>

An OPC Express Interface, known as OPC Xi, was approved in November, 2009, for the [[.NET Framework]].<ref>{{Cite news |work= Automation World |date= December 1, 2009 |title= OPC Xi Interface Approved |url= https://www.automationworld.com/products/control/news/13299096/opc-xi-interface-approved |access-date= October 7, 2021 }}</ref> OPC Xi used [[Windows Communication Foundation]] instead of DCOM, so it can be configured for communication across the enhanced security of [[network address translation]] (NAT).<ref name="gm2009">{{Cite web|title= OPC Xi Updated |author= Gary Mintchell |work= Feed Forward blog |url= http://www.garymintchellsfeedforward.com/feed-forward/2009/11/20/opc-xi-updated.html |date= November 20, 2009 |url-status= dead |archive-date= May 16, 2010 |archive-url= https://web.archive.org/web/20100516163125/http://www.garymintchellsfeedforward.com/feed-forward/2009/11/20/opc-xi-updated.html |access-date= October 7, 2021  }}</ref>

About the same time, the [[OPC Unified Architecture]] (UA) was developed for platform independence.<ref name="gm2009" /> UA can be implemented with [[Java (programming language)|Java]], [[Microsoft .NET]], or [[C (programming language)|C]], eliminating the need to use a [[Microsoft Windows]] platform of earlier OPC versions. UA combined the functionality of the existing OPC interfaces with new technologies such as [[XML]] and [[Web services]] to deliver higher level [[manufacturing execution system]] (MES) and [[enterprise resource planning]] (ERP) support. The first working group for UA met in 2003, version 1.0 was published in 2006.<ref>{{Cite web |title= History |work= OPC Foundation web site |url= https://opcfoundation.org/about/opc-foundation/history/ |access-date= October 7, 2021 }}</ref>

On September 16, 2010, The OPC Foundation and the [[MTConnect]] Institute announced cooperation to ensure interoperability and consistency between the two standards.<ref>{{cite web|url=http://www.opcfoundation.org/Default.aspx/02_news/02_news_display.asp?id=845&MID=News|title=OPC Foundation and MTConnect Institute Announce a Memorandum of Understanding |date= October 21, 2010 |publisher=OPC Foundation |work= Press release |access-date= October 7, 2021  |url-status=dead|archive-url=https://web.archive.org/web/20110616214614/http://www.opcfoundation.org/Default.aspx/02_news/02_news_display.asp?id=845&MID=News|archive-date= June 16, 2011 }}</ref>