Browse Paths

A browse path is a string that represents a path to navigate from one node to another in the OPC UA address space. Browse paths provide a human-readable way to identify nodes using hierarchical names instead of NodeIds, making them essential for dynamic navigation and configuration.

Browse Paths are good alternative to NodeIds when you want to work with node names and their relationships in a more intuitive way.

They allow you to traverse the OPC UA address space without needing to know the exact NodeId of each node, which can be particularly useful in dynamic environments where nodes id may change frequently.

Based on the OPC Foundation Part 4 specification, browse paths follow a specific syntax that supports various reference types, namespace handling, and special characters.

Overview

Browse paths consist of:

• Reference types that define how to navigate between nodes
• Browse names that identify target nodes
• Namespace qualifiers that specify which namespace to use
• Special characters for advanced navigation patterns

Basic Syntax

Simple Hierarchical Navigation

The most common browse path uses forward slashes (/) to follow hierarchical references:

/Objects/DeviceSet/MyDevice/Temperature

This path:

1. Starts at the root /Objects node
2. Follows hierarchical references to DeviceSet
3. Continues to MyDevice
4. Finally reaches Temperature

Namespace Qualification

Namespace index is always required except for the standard namespace (0). When nodes belong to namespaces other than 0, you must prefix the browse name with the namespace index:

/Objects/2:DeviceSet/3:MyDevice/3:Temperature

• Objects has no prefix because it's in the standard namespace 0
• DeviceSet is in namespace 2 and must include the 2: prefix
• MyDevice and Temperature are in namespace 3 and must include the 3: prefix

Important: Only nodes in namespace 0 (the standard OPC UA namespace) can omit the namespace prefix. All other namespaces require explicit qualification.

Reference Types

Browse paths support different reference types to control navigation behavior:

1. Hierarchical References (/)

The forward slash follows any subtype of HierarchicalReferences:

/Objects/Server/ServerStatus/CurrentTime

2. Aggregates References (.)

The period follows any subtype of Aggregates references:

/Objects/Server.NamespaceArray

3. Specific Reference Types (<ReferenceType>)

Use angle brackets to specify exact reference types:

<HasComponent>ServerStatus
<1:ConnectedTo>1:Boiler/1:HeatSensor

Reference Type Modifiers

• Exclude subtypes (#): <#HasComponent> follows only HasComponent, not its subtypes
• Inverse direction (!): <!HasChild>Truck follows inverse HasChild references
• Namespace qualified: <0:HasProperty> specifies the reference type's namespace (required for non-standard namespaces)

Advanced Path Construction

1. Wildcards

Omit the final browse name to match all targets:

/Objects/Server/  # Matches all children of Server
<HasComponent>    # Matches all HasComponent targets

2. Escaping Special Characters

Use & to escape reserved characters in browse names:

Reserved Character	Escaped Form	Example
/	&/	Component&/Name → Component/Name
.	&.	Property&.Value → Property.Value
:	&:	Node&:ID → Node:ID
&	&&	Data&&More → Data&More
<	&<	Value& → Value<Max
>	&>	Value&>Min → Value>Min
#	&#	Tag&#1 → Tag#1
!	&!	Alert&! → Alert!

3. Complex Navigation Examples

Following Multiple Reference Types

<HasComponent>Boiler/<HasProperty>Temperature

1. Follow HasComponent to find Boiler
2. From Boiler, follow HasProperty to find Temperature

Cross-Namespace Navigation

/Objects/2:DeviceSet/<3:ConnectedTo>3:Sensor/3:Value

1. Navigate to DeviceSet in namespace 2
2. Follow ConnectedTo reference (namespace 3) to Sensor
3. Continue to Value property

Inverse Reference Navigation

<!HasChild>2:ParentDevice/2:Configuration

1. Follow inverse HasChild reference to find parent
2. Navigate to Configuration from the parent

Practical Examples

Industrial Automation Scenarios

1. Reading Device Temperature

# Simple hierarchical path
/Objects/DeviceSet/TemperatureSensor01/Temperature

# With namespaces
/Objects/2:DeviceSet/3:TemperatureSensor01/3:Temperature

2. Accessing Method Parameters

# Navigate to method input arguments
/Objects/2:ProductionLine/2:Reactor/2:StartProcess/<HasProperty>InputArguments

3. Finding Connected Equipment

# Follow connection references
/Objects/2:Plant/<2:ConnectedTo>2:Boiler/<HasComponent>HeatingElement

4. Browsing All Alarms

# Wildcard to find all alarm conditions
/Objects/Server/ServerStatus/<HasComponent>

Configuration and Setup

1. Server Information

# Server capabilities
/Objects/Server/ServerCapabilities/MaxBrowseReferences

# Namespace array
/Objects/Server.NamespaceArray

2. Type Definitions

# Browse to custom types
/Types/ObjectTypes/2:CustomDeviceType

# Variable type definitions
/Types/VariableTypes/2:AnalogItemType

Browse Path Validation

1. Syntax Validation

Valid browse path characteristics:

• Starts with a reference type (/, ., or <ReferenceType>)
• Browse names follow the format: [namespace:]name where namespace index is required for all namespaces except 0
• Proper escaping of special characters with &
• Correct reference type syntax with angle brackets

Namespace Rules:

• Standard namespace (0): prefix optional - DeviceSet or 0:DeviceSet
• All other namespaces: prefix required - 2:DeviceSet, 3:MyDevice

2. Common Syntax Errors

Missing Reference Type:

// ❌ Invalid - missing reference type
"Objects/DeviceSet"

// ✅ Valid - starts with reference type
"/Objects/DeviceSet"

Missing Namespace Prefix:

// ❌ Invalid - missing required namespace prefix (assuming DeviceSet is in namespace 2)
"/Objects/DeviceSet/MyDevice"

// ✅ Valid - includes required namespace prefix
"/Objects/2:DeviceSet/2:MyDevice"

// ✅ Valid - standard namespace (0) prefix is optional
"/Objects/DeviceSet" (if DeviceSet is in namespace 0)

Unescaped Special Characters:

// ❌ Invalid - unescaped special characters
"/Objects/Device.Name/Value"

// ✅ Valid - escaped special characters
"/Objects/Device&.Name/Value"

Malformed Reference Types:

// ❌ Invalid - malformed reference type
"<HasComponent/MyDevice"

// ✅ Valid - proper reference type syntax
"<HasComponent>MyDevice"

3. Validation Guidelines

Always specify namespace prefixes for clarity and correctness:

✅ Recommended approach - Always include namespace prefix:

/Objects/0:Server/0:ServerStatus/0:CurrentTime
/Objects/2:DeviceSet/2:TemperatureSensor/2:Value

⚠️ Acceptable but not recommended - Omit prefix only for namespace 0:

/Objects/Server/ServerStatus/CurrentTime

❌ Never omit namespace prefix for non-zero namespaces:

# Wrong - DeviceSet is in namespace 2 but prefix is missing
/Objects/DeviceSet/TemperatureSensor

Best Practices

1. Use Meaningful Names

// ✅ Good - descriptive names
/Objects/ProductionLine/Reactor01/Temperature

// ❌ Avoid - cryptic names
/Objects/PL/R1/T

2. Consistent Namespace Usage

// ✅ Good - consistent namespacing with required prefixes
/Objects/2:DeviceSet/2:TemperatureSensor/2:Value

// ✅ Also good - explicit namespace 0 prefix for clarity
/Objects/0:Server/0:ServerStatus/0:CurrentTime

// ⚠️ Acceptable - mixed namespaces (when nodes are actually in different namespaces)
/Objects/2:DeviceSet/3:TemperatureSensor/3:Value

// ❌ Wrong - missing required namespace prefixes
/Objects/DeviceSet/TemperatureSensor/Value (if not all in namespace 0)

3. Prefer Hierarchical Navigation

// ✅ Good - simple hierarchical path
/Objects/DeviceSet/Device01/Temperature

// ⚠️ Complex - use only when necessary
<HasComponent>DeviceSet/<ConnectedTo>Device01/<HasProperty>Temperature

4. Handle Special Characters Properly

// ✅ Good - properly escaped
/Objects/Device&.Name/Value&:Current

// ❌ Wrong - unescaped special characters
/Objects/Device.Name/Value:Current

Integration with Node-RED

When using browse paths in @opcua/for-node-red nodes:

1. Read Node Configuration

{
    "nodeId": "",
    "browsePath": "/Objects/2:DeviceSet/3:TemperatureSensor/3:Temperature",
    "outputFormat": "value"
}

2. Write Node Configuration

{
    "nodeId": "",
    "browsePath": "/Objects/2:DeviceSet/3:Valve/3:Position",
    "datatype": "Double"
}

3. Dynamic Browse Path Construction

// Build browse path dynamically with proper namespace handling
const deviceId = msg.deviceId || "Device01";
const property = msg.property || "Temperature";
const deviceNamespace = msg.deviceNamespace || "2";

// Always include namespace prefix for non-zero namespaces
const browsePath = `/Objects/${deviceNamespace}:DeviceSet/${deviceNamespace}:${deviceId}/${deviceNamespace}:${property}`;

msg.browsePath = browsePath;
return msg;

Troubleshooting

Common Issues and Solutions

1. "BadBrowseNameInvalid"

   • Check for unescaped special characters (use & for escaping)
   • Verify namespace indices exist on the server
   • Ensure browse names match server exactly (case-sensitive)
   • Most common: Missing required namespace prefix for non-zero namespaces

2. "BadNoMatch"

   • Verify the complete path exists on the server
   • Check namespace indices are correct and exist
   • Ensure proper case sensitivity in browse names
   • Confirm namespace prefixes are included where required

3. "BadReferenceTypeIdInvalid"

   • Verify reference type names are correct and exist
   • Check reference type namespace qualification for custom reference types
   • Ensure reference types exist in the server's type system

4. Performance Issues

   • Use NodeIds instead of browse paths for frequent operations
   • Cache resolved NodeIds when possible
   • Minimize path depth where feasible
   • Consider using subscription instead of repeated browsing

See Also

• NodeIds - Alternative node identification method
• Namespaces - Understanding namespace organization
• OPC Foundation Part 4 Specification - Official browse path specification