Table 1 lists OPC UA definitions which are used in this document, they are included here as a reference. Additional information can be found in the reference documents listed in section 3.
Table 1 – OPC UA Terms and Definitions
|
Term |
Definition |
|
AddressSpace |
The collection of information that an OPC UA Server makes visible to its Clients. See OPC 10000-3 for a description of the contents and structure of the Server AddressSpace. |
|
Attribute |
A primitive characteristic of a Node. All Attributes are defined by OPC UA and may not be defined by Clients or Servers. Attributes are the only elements in the AddressSpace permitted to have data values. See OPC 10000-3 for additional details. |
|
ConformanceUnit |
As defined by the OPC Foundation: a specific set of OPC UA features that can be tested as a single entity. As it applies to MDIS a ConformanceUnit may describe a specific Object or part of a specific Object. It may also describe general functionality such as redundancy or performance. For each ConformanceUnit one or more test cases will exist to ensure that the defined functionality is provided. The test cases may be automatically executed in a Compliance Test Tool (CTT) or they may require some level of manual interaction. See OPC 10000-7 for additional details. |
|
Facet |
A Profile that describes a subset of functionality. This functionality must be paired with other Facets or Profiles to provide an operating Server or Client. See OPC 10000-7 for additional details. |
|
InformationModel |
An organisational framework that defines, characterises and relates information resources of a given system or set of systems. The core address space model supports the representation of InformationModels in the AddressSpace. See OPC 10000-5 for a description of the base OPC UA Information Model. |
|
Method |
A callable software function that is a component of an Object. See OPC 10000-4 for a basic definition. |
|
Node |
The fundamental component of an AddressSpace. See OPC 10000-3 for additional details. |
|
NodeClass |
The class of a Node in an AddressSpace. NodeClasses define the metadata for the components of the OPC UA Object Model. They also define constructs, such as Views, that are used to organise the AddressSpace. See OPC 10000-3 for additional details. |
|
Object |
Objects from an object-oriented technology point of view would have the following definition. Objects share two characteristics: They have state (Attribute) and behaviour (Method). A bicycle has states (current gear, current pedal cadence, current speed) and behaviour (changing gear, changing pedal cadence, applying brakes). An object stores its state in fields (Variables) and exposes its behaviour through functions (Methods). Functions operate on an object's internal state and serve as the primary mechanism for object-to-object communication. Hiding internal state and requiring all interaction to be performed through an object's functions is known as data encapsulation, a fundamental principle of object-oriented programming. In programming languages this object will have a third characteristic: The identity, which will help to find and use the object. From an OPC UA point of view the following definition is used: A Node that represents a physical or abstract element of a system. Objects are modelled using the OPC UA Object Model. Systems, subsystems and devices are examples of Objects. An Object is defined as an instance of an ObjectType. See OPC 10000-3 for additional details. |
|
Object Instance |
A synonym for Object. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
ObjectType |
A Node that represents the TypeDefinition for an Object. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
Profile |
A specific set of capabilities, to which a Server or Client may claim conformance. The capabilities are defined by a set of ConformanceUnits. Each Server or Client may claim conformance to more than one Profile. The OPC Foundation provides a base list of Server and Client Profiles and Facets in an online database which is also documented in an OPC UA specification, OPC 10000-7. The online database can be found here: |
|
Property |
A Variable that is a leaf and cannot have any children. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
Reference |
An explicit relationship (a named pointer) from one Node to another. The Node that contains the Reference is the source Node and the referenced Node is the target Node. All References are defined by ReferenceTypes. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
ReferenceType |
A Node that represents the TypeDefinition of a Reference. The ReferenceType specifies the semantics of a Reference. The name of a ReferenceType identifies how source Nodes are related to TargetNodes and generally reflects an operation between the two, such as “A contains B”. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
UANodeSet |
The root of the AddressSpace defined in an XML document. It defines a set of Nodes, their Attributes and References. See OPC 10000-5 for additional details. |
|
Variable |
Variable is a Node that contains a value and can have children. See OPC 10000-3 and OPC 10000-5 for additional details. |
|
VariableType |
A Node that represents the TypeDefinition for a Variable. See OPC 10000-3 and OPC 10000-5 for additional details. |