This document describes how to map the OPCUA protocol to the W3C Web of Things.
++ + This document is a work in progress +
++ The URL format use the same syntax as per the endpoint in OPCUA. A endpoint physical address available on a network + that allows Clients to access one or more Services provided by a Server. +
+ +opc.tcp://hostname:2655/OPC/Service+ +
The supported protocols are "opc.tcp" and "opcua+uacp"
+| Protocol | +Description | +Reference | +
|---|---|---|
| opc.tcp | +
+ + OPC UA over TCP + + |
+ OPC UA over TCP | +
| opcua+uacp | +OPC UA over WebSocket with binary encoding | ++ OPC UA over WebSockets + | +
| opcua+uajson | +OPC UA over WebSocket with JSON encoding | ++ OPC UA over WebSockets + | +
TODO: Introduce briefly the vocabulary
++ TODO: Describe the allowed terms in a form that use this binding. Provide the terms using the table structure +
+| Vocabulary term | +Description | +Assignment | +Type | +
|---|---|---|---|
opcua:nodeId |
+ refers to a node in the server address space to read write or subscribe to | +mandatory | +string | +
opcua:method |
+ refers to a node in the server address space that indicates the method to call during an action | +mandatory | +string | +
A opcua:nodeId could be provided using different format: string, nodeId, or browse path.
+ns=<namespaceIndex>;<type>=<value>
where:
+<namespaceIndex> is a numeric value representing the index of the corresponding
+ namespace in the namespace array of the server.
+ ns=<namespaceIndex>; can be omitted if the namespace is the default namespace.
+ <type> is either i,s,g, or b
+ <value> depends on <type>| Example | +
|---|
| "ns=1;s=Temperature" |
+
| "i=2258" |
+
| "ns=10;i=1234" |
+
| "ns=10;s=Hello:World" |
+
| "g=09087e75-8e5e-499b-954f-f2a9603db28a" | +
| "ns=1;b=M/RbKBsRVkePCePcx24oRA==" | +
| "ns=1;s=\"QuotedString\"" | +
+ see reference to NodeId definition in the opcua reference + + https://reference.opcfoundation.org/v104/Core/docs/Part6/5.2.2/#Table5 +
++ A browse path is constructed of a starting node and a path. The specified starting Node identifies the node + from which the relative path is based. the path contains a sequence of +
+
+ { root: "i=84", path: "/Objects/1:MySensor/2:ParameterSet/1:Temperature"}
+
the client will use the TranslateBrowsePathsToNodeIds service to translate the browse path to a nodeId.
++ The path string following the description the text format for a RelativePath specified in + BNF representation of a RelativePath +
+ + The table RelativePath Examples Browse Path Description from the OPC UA Reference is reproduced below for convenience. + +| Browse Path | +Description | +
|---|---|
“/2:Block&.Output” |
+ Follows any forward hierarchical Reference with target BrowseName = “2:Block.Output”. | +
“/3:Truck.0:NodeVersion” |
+ Follows any forward hierarchical Reference with target BrowseName = + “3:Truck” and from there a forward Aggregates Reference to a target with BrowseName “0:NodeVersion”. | +
“<1:ConnectedTo>1:Boiler/1:HeatSensor”
+ |
+ Follows any forward Reference with a BrowseName = + ‘1:ConnectedTo’ and finds targets with BrowseName = ‘1:Boiler’. From there follows any hierarchical + Reference and find targets with BrowseName = ‘1:HeatSensor’. + | +
“<1:ConnectedTo>1:Boiler/” |
+ Follows any + forward Reference with a BrowseName = ‘1:ConnectedTo’ and finds targets with BrowseName = + ‘1:Boiler’. From there it finds all targets of hierarchical References. + | +
“<0:HasChild>2:Wheel” |
+ + Follows any forward Reference with a BrowseName = ‘HasChild’ and qualified with the default OPC UA + namespace. Then find targets with BrowseName = ‘Wheel’ qualified with namespace index ‘2’. + | +
“<!HasChild>Truck” |
+ + Follows any inverse Reference with a BrowseName = ‘HasChild’. Then find targets with BrowseName = + ‘Truck’. In both cases, the namespace component of the BrowseName is assumed to be 0. “<0:HasChild>” + Finds all targets of forward References with a BrowseName = ‘HasChild’ and qualified with the + default OPC UA namespace. + | +
| Value | +Description | +
|---|
Map WoT Interaction model verbs to default values if any
+| Operation | +Default Biding | +
|---|---|
readproperty |
+
+
+ Read
+
+ |
+
writeproperty |
+
+ Write
+
+ |
+
subscribe |
+
+
+ CreateMonitoredItems
+
+ |
+
+ TODO: This section should describe other mappings that can be used by TD designers. It is meant to be + informative but it provides guidelines for implementers. +
++ the OPCUA-JSON codec payload format follow the OPCUA JSON data encoding format defined in + reference.opcfoundation.org/Core/docs/Part6/5.4.1 +
+ +
+{
+ "@context": "https://www.w3.org/2019/wot/td/v1",
+ "@type": ["Thing"],
+
+ securityDefinitions: { nosec_sc: { scheme: "nosec" } },
+ security: "nosec_sc",
+
+ title: "servient",
+ description: "node-wot CLI Servient",
+
+ opcua: {
+ namespace: [
+ "http://opcfoundation.org/UA",
+ "own",
+ "http://opcfoundation.org/UA/DI/"
+ ]
+ },
+ base: "opc.tcp://localhost:26543",
+ properties: {
+ Temperature: {
+ description: "the temperature in the room",
+ observable: true,
+ readOnly: true,
+ unit: "°C",
+ "opcua:nodeId": { root: "i=84", path: "/Objects/1:MySensor/2:ParameterSet/1:Temperature" },
+ forms: [
+ {
+ type: "object",
+ href: "", // endpoint,
+ op: ["readproperty", "observeproperty"],
+ },
+ {
+ type: "number",
+ href: "", // endpoint,
+ op: ["writeproperty"],
+ },
+ ],
+ },
+ TemperatureSetPoint: {
+ description: "the temperature set point",
+ observable: true,
+ readOnly: false,
+ unit: "°C",
+ forms: [
+ {
+ type: "object",
+ href: endpoint,
+ op: ["readproperty", "observeproperty", "writeproperty"],
+ "opcua:nodeId": { root: "i=84", path: "/Objects/1:MySensor/2:ParameterSet/1:TemperatureSetPoint" },
+ },
+ ],
+ },
+ }
+}
+
+