3 Terms, definitions and conventions ToC Previous Next

3.3 Conventions for Service definitions ToC Previous Next

OPC UA Services contain parameters that are conveyed between the Client and the Server. The OPC UA Service specifications use tables to describe Service parameters, as shown in Table 1. Parameters are organised in this table into request parameters and response parameters.

Table 1 – Service Definition Table

Name Type Description
Request   Defines the request parameters of the Service
   Simple Parameter Name   Description of this parameter
   Constructed Parameter Name   Description of the constructed parameter
      Component Parameter Name   Description of the component parameter
Response   Defines the response parameters of the Service

The Name, Type and Description columns contain the name, data type and description of each parameter. All parameters are mandatory, although some may be unused under certain circumstances. The Description column specifies the value to be supplied when a parameter is unused.

Two types of parameters are defined in these tables, simple and constructed. Simple parameters have a simple data type, such as Boolean or String.

Constructed parameters are composed of two or more component parameters, which can be simple or constructed. Component parameter names are indented below the constructed parameter name.

The data types used in these tables may be base types, common types to multiple Services or Service-specific types. Base data types are defined in OPC 10000-3. The base types used in Services are listed in Table 2. Data types that are common to multiple Services are defined in Clause 7. Data types that are Service-specific are defined in the parameter table of the Service.

Table 2 – Parameter Types defined in OPC 10000-3

Parameter Type

The parameters of the Request and Indication service primitives are represented in Table 1 as Request parameters. Likewise, the parameters of the Response and Confirmation service primitives are represented in Table 1 as Response parameters. All request and response parameters are conveyed between the sender and receiver without change. Therefore, separate columns for request, indication, response and confirmation parameter values are not needed and have been intentionally omitted to improve readability.

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