How can you use the OPC Web Client?

The quick answer is that you can create almost any kind of application in virtually all containers. In fact, almost every conceivable way of developing an OPC Client is possible...

winforms   web forms   services shell scripts

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Question: Do you have direct access to an OPC Server?

Yes:

You can connect to one or multiple local/or remote OPC Servers, with a single instance of the the control. You can use the .NET or ActiveX components that utilize COM/DCOM as the underlying transport.

No:

If your application/system has support for Web Services then you may be able to use XML messaging to read/write to your OPC Server(s) Tag(s). Because HTTP is the underlying transport, this makes the OPC Web Service truly firewall-friendly.

Question: Is this an Enterprise application requiring a Web Service?

Web Service are fast becoming the defacto standard for universal data communications. As self-describing components that are accessible over the internet, web services enable enterprise-level applications/systems to share data to/from each other.

In this case, the OPC Web Service allows XML clients to send/receive XML messages that are in turn sent to your OPC Server(s). The OPC Web Service is essentially an XML-to-OPC gateway.

HTTP is the underlying transport making the OPC Web Service truly firewall-friendly.