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wilamowski-b-m-irwin-j-d-industrial-communication-systems-2011

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57-6 Industrial Communication Systems<br />

Data change<br />

notifications<br />

Read/write<br />

Object<br />

Variables<br />

x<br />

y<br />

z<br />

References to<br />

other objects<br />

Invoke<br />

Event<br />

notifications<br />

Methods<br />

X0<br />

Y0<br />

Z0<br />

FIGURE 57.7<br />

UA object model.<br />

Node<br />

Attributes<br />

x<br />

y<br />

z<br />

References<br />

T0<br />

U0<br />

V0<br />

Attributes describe a Node<br />

References define relationship<br />

to other Nodes<br />

Node<br />

FIGURE 57.8<br />

UA AddressSpace node model.<br />

References are used to relate Nodes to each other. They can be accessed using the browsing and<br />

querying services. Like Attributes, they are defined as fundamental components of Nodes. Unlike<br />

Attributes, References are defined as instances of ReferenceType Nodes. ReferenceType Nodes are visible<br />

in the AddressSpace and are defined using the ReferenceType NodeClass.<br />

The Node that contains the Reference is referred to as the SourceNode and the node that is referenced<br />

is referred to as the TargetNode (see Figure 57.9). The combination of the SourceNode, the ReferenceType,<br />

SourceNode<br />

Attributes<br />

x<br />

y<br />

z<br />

ReferenceName<br />

(name of the<br />

reference’s<br />

ReferenceType)<br />

TargetNode<br />

FIGURE 57.9<br />

UA reference model.<br />

© <strong>2011</strong> by Taylor and Francis Group, LLC

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