Version Info

The XHDASrv OPC Historian Web Service is superseded by the XiTOCO OPC Xi Converter server. XHDASrv was introduced by Advosol because the OPC Foundation didn't specify a web service interface as it did with XML DA for OPC Data Access. Since the OPC Foundation adopted the Express Interface specification as the OPC Xi interface there is a standardized web services interface with OPC HDA functionality. The XiTOCO OPC Xi Converter server enables OPC Xi client applications to access OPC DA, AE and HDA servers through secure communication that is based on WCF (Windows Communication Foundation)       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 XHDAS OPC Historian Web Service defines a web interface in a similar way as the OPC XML DA specification does for OPC DA.

The OPC Historian Web Service is installed as a .Net web service on a machine near the OPC HDA server, best on the same machine to minimize DCOM configuration issues. 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 a test client.

The client interface is defined in the supplied WSDL file and all methods are explained in the comprehensive reference documenation help file.

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

The available server access methods are:

• Browse (with multiple filter options)
• GetStatus
• GetProperties (returns server capabilities, attributes and aggregates)
• ReadRaw
• ReadProcessed
• ReadModified
• ReadAtTime
• ReadAttributes
• ReadAnnotations
• Insert
• Replace
• InsertReplace
• DeleteRaw
• DeleteAtTime

Requirements
	Windows Vista, Windows XP, Windows 2000 or Windows 2003 Server
	.NET Framework 1.1/2/3/3.5 and IIS
	OPC HDA V1.2 Server

XMLDA.NET is a .NET XML DA client component that supports access to OPC DA and XML DA servers. The OPC client application can be designed as an XML DA web service client and ican be built as a Windows Forms orASP.NET application. All DCOM handling is XMLDA.NET internally.