This clause specifies the OPC UA Services. The OPC UA Servicedefinitions are abstract descriptions and do not represent a specification for implementation. The mapping between the abstract descriptions and the Communication Stackderived from these Servicesare defined in OPC 10000-6. In the case of an implementation as web services, the OPC UA Servicescorrespond to the web service and an OPC UA Servicecorresponds to an operation of the web service.

These Servicesare organised into Service Sets. Each Service Setdefines a set of related Services. The organisation in Service Setsis a logical grouping used in this standard and is not used in the implementation.

The Discovery Service Set, illustrated in Figure 1, defines Servicesthat allow a Clientto discover the Endpointsimplemented by a Serverand to read the security configuration for each of those Endpoints.

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Figure 1– Discovery Service Set

The SecureChannel Service Set, illustrated in Figure 2, defines Servicesthat allow a Clientto establish a communication channel to ensure the Confidentialityand Integrityof Messagesexchanged with the Server.

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Figure 2– SecureChannel Service Set

The Session Service Set, illustrated in Figure 3, defines Servicesthat allow the Clientto authenticate the user on whose behalf it is acting and to manage Sessions.

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Figure 3– Session Service Set

The NodeManagement Service Set, illustrated in Figure 4, defines Servicesthat allow the Clientto add, modify and delete Nodesin the AddressSpace.

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Figure 4– NodeManagement Service Set

The View Service Set, illustrated in Figure 5, defines Servicesthat allow Clientsto browse through the AddressSpaceor subsets of the AddressSpacecalled Views. The Query Service Setallows Clientsto get a subset of data from the AddressSpaceor the View.

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Figure 5– View Service Set

The Attribute Service Setis illustrated in Figure 6. It defines Servicesthat allow Clientsto read and write Attributesof Nodes, including their historical values. Since the value of a Variableis modelled as an Attribute, these Servicesallow Clientsto read and write the values of Variables.

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Figure 6– Attribute Service Set

The Method Service Setis illustrated in Figure 7. It defines Servicesthat allow Clientsto call methods. Methods run to completion when called. They may be called with method-specific input parameters and may return method-specific output parameters.

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Figure 7– Method Service Set

The MonitoredItem Service Setand the Subscription Service Set, illustrated in Figure 8, are used together to subscribe to Nodesin the OPC UA AddressSpace.

The MonitoredItem Service Setdefines Servicesthat allow Clientsto create, modify, and delete MonitoredItemsused to monitor Attributes for value changes and ObjectsforEvents.

These Notificationsare queued for transfer to the Clientby Subscriptions.

The Subscription Service Setdefines Servicesthat allow Clientsto create, modify and delete Subscriptions. Subscriptionssend Notificationsgenerated by MonitoredItemsto the Client. Subscription Servicesalso provide for Clientrecovery from missed Messagesand communication failures.

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Figure 8– MonitoredItem and Subscription Service Sets