For the purposes of this document, the following terms apply.

collection of information that a Servermakes visible to its Clients

Note 1to entry: See OPC 10000-3for a description of the contents and structure of the ServerAddressSpace.

function that calculates derived values from Raw data

Note 1to entry: Raw data may be from a historian or buffered real time data. Common Aggregates include averages over a given time range, minimum over a time range and maximum over a time range.

type of Event associated with a state condition that typically requires acknowledgement

Note 1to entry: See OPC 10000-9for a description of Alarms.

primitive characteristic of a Node

Note 1to entry: All Attributes are defined by OPC UA, and may not be defined by Clientsor Servers. Attributes are the only elements in the AddressSpace permitted to have data values.

intermediary program module that routes NetworkMessagesfrom Publishersto Subscribers

Note 1to entry: Brokersare building blocks of Message Oriented Middleware.

digitally signed data structure that contains a public key and an identity

Note 1to entry: Certificates are used to identity for example Clients, Servers, users and certificate authorities.

software application that sends Messagesto OPC UAServersconforming to the Servicesspecified in this set of specifications

generic term that is an extension to an Event

Note 1to entry: A Conditionrepresents the conditions of a system or one of its components and always exists in some state.

layered set of software modules between the application and the hardware that provides various functions to encode, encrypt and format a Messagefor sending, and to decode, decrypt and unpack a Messagethat was received

data that is composed of elements of more than one primitive data type, such as a structure

list of named data values

Note 1to entry: A DataSettypically consists of Eventfields or Variablevalues..

payload of a NetworkMessagecreated from a DataSet

Note 1to entry:  The DataSetMessageis an immutable payload of the NetworkMessagehanded off to the Message Oriented Middleware(transport layer) for delivery by the Publisher. The Subscriberreceives the DataSetMessageas the payload of a NetworkMessage from the Publisherwith additional headers that may be supplied by the Message Oriented Middlewarealong the way.

process by which Clientobtains information about Servers, including endpoint and security information

generic term used to describe an occurrence of some significance within a system or system component

special Attributeof a Nodethat signifies that a Clientmay subscribe to that particular Nodeto receive Notificationsof Eventoccurrences

organizational framework that defines, characterizes and relates information resources of a given system or set of systems.

Note 1to entry: The core AddressSpace model supports the representation of Information Models in the AddressSpace. See OPC 10000-5for a description of the base OPC UA Information Model.

data unit conveyed between Clientand Serverthat represents a specific Servicerequest or response

infrastructure supporting sending and receiving NetworkMessagesbetween distributed systems

Note 1to entry: An OPC UA Applicationmay support different types of Message Oriented Middlewareinfrastructures and protocols like AMQP, MQTT, or UDP with IP multicast. Other types like DDS or XMPP can also be integrated into the OPC UA PubSubmodel.

callable software function that is a component of an Object

Client-defined entity in the Serverused to monitor Attributes or EventNotifiersfor new values or Event occurrences and that generates Notifications for them

DataSetMessagesand header to facilitate delivery, routing, security and filtering

Note 1to entry: The Publisherhands off the NetworkMessageto the Message Oriented Middleware(transport layer) to deliver DataSetMessagesto the Subscribers.

Note 2 to entry: The term message is used with various connotations in the messaging world. The Publishermight like to think of the message as an immutable payload handed off to the Message Oriented Middlewarefor delivery. The Subscriberoften thinks of the message as not only that immutable payload from the sender, but also various annotations supplied by the Message Oriented Middlewarealong the way. To avoid confusion the term DataSetMessageis used to mean the message as supplied by the Publisherfor a DataSetand the term NetworkMessageis used to mean the DataSetMessageplus sections for annotation at the head and tail of the DataSetMessage.

fundamental component of an AddressSpace

class of a Node in an AddressSpace

Note 1to entry: NodeClasses define the metadata for the components of the OPC UA object model. They also define constructs, such as Views, that are used to organize the AddressSpace.

generic term for data that announces the detection of an Event or of a changed Attribute value; Notifications are sent in NotificationMessages.

Message published from a Subscription that contains one or more Notifications

Node that represents a physical or abstract element of a system

Note 1to entry: Objects are modelled using the OPC UA Object Model. Systems, subsystems and devices are examples of Objects. An Object may be defined as an instance of an ObjectType.

synonym for Object

Note 1to entry: Not all Objects are defined by ObjectTypes.

Node that represents the type definition for an Object

Client, which calls OPC UA Services,or a Server, which performs those Services, or an OPC UA Publisheror an OPC UA Subscriber.

entity sending NetworkMessagesto a Message Oriented Middleware

Note 1to entry: A Publisher can be a native OPC UA Application or an application that only has knowledge about the Message Oriented Middleware and the rules for encoding the NetworkMessages and DataSetMessages.

OPC UA variant of the publish subscribe messaging pattern

specific set of capabilities to which a Servermay claim conformance.

Note 1to entry: Each Servermay claim conformance to more than one Profile

Note 2 to entry: The set of capabilities are defined in OPC 10000-7

executable Object that, when invoked, immediately returns a response to indicate that execution has started, and then returns intermediate and final results through Subscriptions identified by the Clientduring invocation

explicit relationship (a named pointer) from one Node to another

Note 1to entry: The Node that contains the Reference is the source Node, and the referenced Node is the target Node. All References are defined by ReferenceTypes.

Node that represents the type definition of a Reference

Note 1to entry: The ReferenceType specifies the semantics of a Reference. The name of a ReferenceType identifies how source Nodes are related to target Nodes and generally reflects an operation between the two, such as “A contains B”.

software application that implements and exposes the Servicesspecified in this set of specifications

Client-callable operation in a Server

Note 1to entry: Servicesare defined in OPC 10000-4. A Serviceis similar to a method call in a programming language or an operation in a Web services WSDL contract.

group of related Services

logical long-running connection between a Clientand a Server.

Note 1to entry: ASessionmaintains state information between Servicecalls from the Clientto the Server.

entity receiving DataSetMessagesfrom a Message Oriented Middleware

Note 1to entry: A Subscribercan be a native OPC UA Applicationor an application that has just knowledge about the Message Oriented Middlewareand the rules for decoding the NetworkMessagesand DataSetMessages. A Subscriptionin the OPC UA Client Servermodel has a different meaning than the Subscriberin the PubSubmodel.

Client-defined endpoint in the Server,used to return Notifications to the Client

Note 1to entry: Subscriptionis a generic term that describes a set of Nodes selected by the Client(1) that the Serverperiodically monitors for the existence of some condition, and (2) for which the Serversends Notifications to the Clientwhen the condition is detected.

hardware or software platforms that exist as an independent entity. UA Applicationsare dependent on an entity’s existence in order to perform UA services. However, the entity is not dependent on UA Applications.

Note 1to entry: Hardware and software platforms include physical hardware, firmware, operating system, networking, non-UA applications, as well as other UA Applications. A Distributed Control System, PLC/Device, and UA Server are examples of an Underlying System.

Nodethat contains a value

specific subset of the AddressSpace that is of interest to the Client.