3 Terms, definitions, abbreviated terms and conventions

3.1 Terms and definitions

For the purposes of this document, the terms and definitions given in OPC 10000-1, OPC 10000-2, OPC 10000-3, and the following apply.

3.1.1 Active Server

Server which is currently sourcing information

3.1.2 Deadband

permitted range for value changes that will not trigger a data change Notification

3.1.3 DiscoveryEndpoint

Endpoint that allows Clients access to Discovery Services without security

3.1.4 Endpoint

physical address available on a network that allows Clients to access one or more Services provided by a Server

3.1.5 EphemeralKey

public-private key pair generated for each execution of a key establishment process.

3.1.6 Failed Server

Server that is not operational.

3.1.7 Failover

act of switching the source or target of information.

3.1.8 Gateway Server

Server that acts as an intermediary for one or more Servers

3.1.9 HostName

unique identifier for a machine on a network

3.1.10 Redundancy

presence of duplicate components enabling the continued operation after a failure of an OPC UA component

3.1.11 RedundantServerSet

two or more Servers that are redundant with each other

3.1.12 SecurityToken

identifier for a cryptographic key set

3.1.13 ServerUri

ApplicationUri for a Server

3.1.14 SoftwareCertificate

digital certificate for a software product that can be installed on several hosts to describe the capabilities of the software product

3.2 Abbreviated terms

• API Application Programming Interface

• BNF Backus-Naur Form

• CA Certificate Authority

• CRL Certificate Revocation List

• CTL Certificate Trust List

• DA Data Access

• ECC Elliptic Curve Cryptography

• GDS Global Discovery Server

• JWT JSON Web Token

• NAT Network Address Translation

• RSA Rivest, Shamir and Adleman [Public Key Encryption System]

• UA Unified Architecture

• URI Uniform Resource Identifier

• URL Uniform Resource Locator

3.3 Conventions for Service definitions

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 organized in this table into request parameters and response parameters.

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.

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.