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NodeId

In OPC UA, a NodeId serves as the unique identifier for nodes within the server's Address Space. Understanding how to interpret and use a NodeId is key to effectively navigating and accessing data in an OPC UA environment.

Here is a more detailed explanation.

Understanding NodeId Components.

A NodeId in OPC UA is composed of three main elements:

  • Namespace Index: This is a number that refers to a specific namespace. Namespaces are used in OPC UA to avoid identifier conflicts by grouping identifiers into different contexts. Each OPC UA server defines its own set of namespaces. The Namespace Index is a pointer to one of these namespaces.

  • Identifier: The actual unique identifier within the namespace. It can be of various types - numeric, string, globally unique identifier (GUID), or binary.

  • Identifier Type: This specifies the type of the Identifier (numeric, string, GUID, or binary). The type needs to be known to interpret the Identifier correctly.

NodeId notation: An Example

Let's examine a specific example of a NodeId in Binary Numeric Character (BNC) format:

Suppose we have a NodeId with a Namespace Index of 3, an Identifier Type of Numeric, and an Identifier of 12345.

In BNC form, this NodeId is represented as ns=3;i=12345.

Here, ns=3 denotes that the Namespace Index is 3, which tells us which namespace to look in.

The i=12345 part signifies that the Identifier is numeric and its value is 12345. Practical Application

In a practical scenario, such as interfacing with an OPC UA server, you would use this NodeId to reference a specific node. For instance, if this NodeId represents a specific sensor in a manufacturing process, you would use ns=3;i=12345 to access data from this sensor.

Understanding NodeIds allows you to accurately identify and interact with various nodes in the OPC UA server's Address Space, whether they are data points, devices, or functions. This knowledge is essential for anyone working with OPC UA, as it is the foundation for data exchange and interaction within this environment.

the Server Namespace Array​

In OPC UA, the Namespace Array is a list of Namespace URIs that the server supports. It is a key component of the OPC UA server's Address Space, as it defines the context for all the identifiers used in the Address Space.