Architecture OPC UA: exam questions with worked answers

Questions for the "Architecture" topic

1. Q01

   OPC UA supports two communication patterns: Client/Server (the classic Request/Response model) and Pub/Sub (publish/subscribe over MQTT or UDP multicast/unicast), the latter introduced in version 1.04 to address Industrie 4.0 use cases.

   TrueFalse

   1. Architecture· Client/Server vs. Pub/Sub· Medium

   ▸

   Correct answer

   True

   Learning tip

   OPC UA is dual-mode by design. Client/Server has been in the standard since version 1.0 and exposes bidirectional services such as Read, Write and Subscribe. Pub/Sub was added in 1.04 (2018) with transport bindings over MQTT, AMQP or UDP, which scales much better for IIoT and cloud telemetry. Both modes can coexist inside the same device, and the typical split is Client/Server for configuration and engineering access, Pub/Sub for high-volume telemetry.

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2. Q02

   The OPC UA Address Space is a hierarchical structure of Nodes linked by typed References (HasComponent, HasProperty, HasTypeDefinition, etc.), exposed as a graph that clients can walk through the Browse service.

   TrueFalse

   1. Architecture· Address Space· Medium

   ▸

   Correct answer

   True

   Learning tip

   The Address Space is effectively the object filesystem of an OPC UA server. Nodes come in eight NodeClasses (Variable, Object, Method, ObjectType, VariableType, DataType, ReferenceType, View), each identified by a unique NodeId built from a namespace index and an identifier. Nodes are linked by typed References, and human-readable BrowseName/DisplayName attributes make navigation usable. The Browse service lets a client discover the structure dynamically without prior knowledge of the vendor model.

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