Version Info

The XHDASrv OPC Historian Web Service exposes an OPC HDA server as a .Net web service. Data archived in OPC HDA servers can be accessed through firewalls from any location. The OPC Historian Web Service does not store any data. It forwards client calls to the associated OPC HDA server and passes the retrieved data back to the client application.

When to use the OPC Historian Web Service?
The typical reason to use the OPC Historian Web Service is to access an OPC HDA server from a remote location. The communication protocols used by web services can pass firewalls and access servers anywhere on an Intranet or on the Internet.
Web services also offer more flexibilty and clients can be easily implemented on other platforms such as Linux.

How to use the OPC Historian Web Service?
Client applications reference the the WSDL file supplied with OPC Historian Web Service and use the proxy methods created by the .Net compiler or a web service development tool on other platforms.
There is no OPC specification for a Historian web service. The OPC Historian Web Service defines an interface that is close to the OPC HDA specification in a similar way as this is done in the .Net interface for OPC Data Access servers, where there is also no specification.

The OPC Historian Web Service is installed as a .Net web service on a machine near the OPC HDA server. The ProgID of the OPC HDA server is defined in the web.config file. No other configuration is required. A sample web service client application is provided and can be used as test client.

The client interface is defined in the supplied WSDL file and a help documentation that can be viewed externally or plugged into Visual Studio describes the interface methods created from the WSDL file.

Users with knowledge of OPC HDA can create a web client application in minutes.

Requirements
	Windows XP, Windows 2000 or Windows 2003 Server
	.NET Famework and IIS
	OPC HDA V1.2 Web Service