Interacting with DSC Module Web Services (DSC Module)

LabVIEW Web services allow Web browsers and HTTP-capable clients to interact with LabVIEW applications. You use URLs and HTTP methods to transmit data to the Web service. The LabVIEW Datalogging and Supervisory Control (DSC) Module includes built-in Web services that expose DSC Module VIs functionality. The DSC Module includes the following Web services:

• Alarms & Events Web service—Web service for sending and receiving alarm and event information. Use the name nialarm when referring to this Web service in a URL.
• Citadel Web service—Web service for querying historical data in the Citadel database. Use the name nicitadel when referring to this Web service in a URL.

Accessing the DSC Module Web Services

In a Web browser or other Web client, you use URLs and HTTP methods to exchange information with the Web service, as well as send values as post data using the POST HTTP method. Refer to the World Wide Web Consortium at www.w3.org for more information about HTTP method definitions, including the POST method.

The following figure shows an example URL that a Web client might use to exchange data with the Alarms & Events Web service, nialarm.

• IP address or computer name—If the Web client accesses the Web service from the same machine running the Web Server, use the value localhost. If the Web client accesses a Web service on a remote target, use the target's IP address or machine name.
• Port—Specifies the HTTP port of the Web Server hosting the Web service. The DSC Module Web services use the system Web server, whose port is 3580.
• Web service name—Specifies the name of the DSC Module Web service.
• Web method—Specifies the name of the functionality in the DSC Module Web service you want to interact with.
• Tag URL—Specifies the network path to the shared variable or process you want to interact with.
• Input parameters—Specifies the input parameters of the Web method. The URL assigns default input parameter(s) if you do not specify any input parameters.

DSC Module Web services can return data as XML- or JSON-formatted responses. By default, the DSC Module Web services return XML-formatted responses.

Error Handling

After responding to a client request, the Web service displays a response message in the HTTP header. The HTTP header describes whether an operation succeeds or fails. If an operation succeeds, the Reason-Phrase field in the HTTP header is empty. If an operation fails, the Reason-Phrase field in the HTTP header contains information about the failure, such as the LabVIEW error code and explanation of the error.