Presentation by Jose Manuel Cantera Fonseca Senior Expert, FIWARE Foundation e.V. FIWARE Global Summit 21-22 May 2019 - Genoa, Italy

1. Web of Things
The way towards interoperability with NGSI-LD
José Manuel Cantera Fonseca – FIWARE Foundation
May 2019 – FIWARE Summit Genoa

2. 1
WoT Introduction (I)
• The W3C Web of Things (WoT) has been created to enable
interoperability across IoT Platforms and application domains.
• WoT provides mechanisms to formally describe IoT interfaces:
• allowing IoT devices and services to communicate with each other
• independent of the underlying implementation
• across multiple networking protocols

3. 2
WoT Interaction Model
• WoT applications use three types of Interaction Affordances:
• Properties
• Expose internal state of the Thing that can be directly accessed (read) and
optionally manipulated (write) or watched (observe) i.e. pull and push
communication styles.
• Actions
• allow to invoke a function or service exposed by the Thing or to trigger a
process
• Events
• Thing-initiated notifications, discrete events, or streams of values sent
asynchronously to the receiver. Push communication style.

4. 3
WoT Building Blocks
• Thing Description (TD): it describes the network-facing
interface of a Thing. Each WoT Device MUST have a
corresponding TD. Normative
• Binding Templates can be used to describe multiple protocol
bindings, so that a Thing can communicate with different IoT
Platforms. Non-normative.
• Scripting API enables implementation of the application logic
of a Thing using a standardized contract for JavaScript. Non-
normative
• Status: Thing Description is expected to be a W3C
Recommendation in Q2 2019
• Note: This presentation is based on CR WoT specifications.
Source: W3C

5. 4
W3C WoT Architectural elements & patterns
Source: W3C
Servient as a Thing
Servient as a Intermediary
• A Servient is a software stack that implements the WoT building blocks.
• Servients can host and expose Things and/or consume Things (i.e., host Consumers)
• Depending on the Protocol Binding, Servients can perform in both server and client role

6. 5
WoT Thing Description (WoT TD)
• It defines an information model based on a semantic vocabulary and a serialized
representation based on JSON. (but also allows JSON-LD processing).
• The index.html for Things, human-readable and machine-understandable metadata:
• Thing instances general metadata such as name, ID, descriptions
• Web Links to related Things or other documents.
• Interaction Affordance metadata (properties, actions, events)
• Public Security Configuration metadata
• Schemata of the information exchanged with the Thing (using JSON Schema).
• TD can be hosted locally by a Thing or externally (ex. by a Thing Catalogue)

7. 6
Thing Description (TD) Information Model
source: W3C

8. 7
TD Example (I). (HTTPs)
source: W3C
{
"id": "urn:dev:wot:com:example:servient:lamp",
"@type": "Thing",
"name": "MyLampThing",
"securityDefinitions": {
"basic_sc": {"scheme": "basic", "in":"header"}
},
"security": ["basic_sc"],
"properties": {
"status" : {
"type": "string",
"forms": [{"href": "https://mylamp.example.com/status"}]
}
},
"actions": {
"toggle" : {
"forms": [{"href": "https://mylamp.example.com/toggle"}]
}
},
"events":{
"overheating":{
"data": {"type": "string"},
"forms": [{
"href": "https://mylamp.example.com/oh",
"subprotocol": "longpoll"
}]
}
},
"@context": "https://www.w3.org/2019/wot/td/v1"
}
source: W3C

9. 8
TD Example (II) (MQTT)
source: W3C
{
"id": "urn:dev:ops:32473-WoTLightSensor-1234",
"@type": "Thing",
"name": "MyLightSensor",
"securityDefinitions": {
"nosec_sc": {
"scheme": "nosec"
}
},
"security": [
"nosec_sc"
],
"events": {
"luminosityValue": {
"data": {
"type": "integer"
},
"forms": [
{
"href": "mqtt://192.168.1.187:1883/lightSensor",
"contentType": "text/plain"
}
]
}
},
"@context": "https://www.w3.org/2019/wot/td/v1"
}
source: W3C

10. 9
TD with SAREF semantic annotations
source: W3C
{
"id": "urn:dev:wot:com:example:servient:lamp",
"name": "MyLampThing",
"@type": "saref:LightingDevice",
"securityDefinitions": {"basic_sc": {
"scheme": "basic",
"in": "header"
}},
"security": ["basic_sc"],
"properties": {
"status": {
"@type": "saref:OnOffState",
"type": "string",
"forms": [{
"href": "https://mylamp.example.com/status"
}]
}
},
"actions": {
"toggle": {
"@type": "saref:ToggleCommand",
"forms": [{
"href": "https://mylamp.example.com/toggle"
}]
}
},
"events": {
"overheating": {
"@type": "saref:NotifyCommand",
"data": {"type": "string"},
"forms": [{
"href": "https://mylamp.example.com/oh"
}]
}
},
"@context": [
"https://www.w3.org/2019/wot/td/v1",
{
"saref": "https://w3id.org/saref#"
}
SAREF can be used to
annotate TDs
source: W3C

11. 10
WoT ßà NGSI-LD Interworking (IoW) principles
§ Overall Architecture:
§ NGSI-LD : Information Management Layer
§ WoT : IoT Service Layer
§ Proposed Interworking mechanism. An “NGSI-LD-WoT Intermediary” to
play a dual role:
§ NGSI-LD Context Source
§ WoT Intermediary Servient
§ NGSI-LD-WoT Intermediary responsibilities:
§ Act as an Intermediary Servient to Things
§ Perform NGSI-LD mappings for WoT Events, Properties and Actions
§ Using extra semantic annotations added to the TD
§ ”Similar process” to what currently the IoT Agents do
§ Expose WoT Properties as NGSI-LD Attributes (Context Source)
§ Propagate WoT Event data to an NGSI-LD Context Broker
§ (the intermediary does not have data storage capabilities itself)
§ Export WoT Actions as NGSI-LD Actuations (see next slides)

12. 11
WoT ßà NGSI-LD Interworking. Conceptual architecture
NGSI-LD
Context Broker
WoT Intermediary
(CSource)
WoT Thing
Thing
Descriptors
Client
Applications
NGSI-LD API
(Entities)
WoT Thing
WoT Things
Thing Description
(Entity2Thing
)
(Things)
Semantic
Annotations
(Thing2Entity
)
Semantic
Annotations

13. 12
WoT ßà NGSI-LD Interworking (mappings)
§ Proposed Mappings
WoT Affordance NGSI-LD Element
Property Attribute (Property or Relationship)
Event Attribute (Property or Relationship)
Action "hasActuation" Relationship. NEW
"saref:hasCommand" Property. ETSI SAREF
"sosa:Actuation" Entity Type. W3C SSN
§ Mapping process can be guided through TD annotations expressed
using standard ontologies
§ W3C SSN
§ ETSI SAREF
§ ….

14. 1
3
TD with NGSI-LD IoW semantic annotations (I)
source: W3C
{
"id": "urn:dev:ops:32473-WoT-ContainerSensor-1234",
"name": "Sensor-Brand-Model",
"securityDefinitions": {
"nosec_sc": {
"scheme": "nosec"
}
},
"security": [
"nosec_sc"
],
"events": {
"fillingValue": {
"@type": "sosa:Observation",
"sosa:hasFeatureOfInterest": "urn:ngsi-ld:WasteContainer:A3456",
"sosa:observedProperty": "https://uri.fiware.org/ns/dataModels/fillingLevel",
"data": {
"type": ”number"
},
"forms": [
{
"href": "mqtt://192.168.1.187:1883/WasteContainer/1234",
"contentType": "text/plain"
}
]
}
},
"@context": [
"https://www.w3.org/2019/wot/td/v1",
{
"sosa": "http://www.w3.org/ns/sosa/"
}
]
}
W3C SSN
Annotations for
NGSI-LD Mapping
{
"id": "urn:ngsi-ld:WasteContainer:A3456 ",
"type": ”WasteContainer",
"fillingLevel": {
"type”: "Property",
"value" : 0.85,
"observedAt" : “2019-22-05T12:34:55Z”,
"source" : "urn:dev:ops:32473-WoT-ContainerSensor-1234"
},
"color" : {
"type”: "Property",
"value”: "green"
},
"@context": [
"https://schema.lab.fiware.org/ld/context",
"https://uri.etsi.org/ngsi-ld/v1"
]
}
Event Mapping

15. 14
WoT Action ßà NGSI-LD IoW Proposal
§ New terms introduced:
§ hasCommand Property (reused from SAREF). A collection of actuatable
commands
§ hasActuation Relationship. NEW. A collection of actuations (sosa:Actuation)
§ sosa:Actuation Entity Type. (reused from W3C SSN)
§ For each WoT Action concerning an NGSI-LD Entity:
§ hasCommand contains the concerned command (ex. saref:ToggleCommand)
§ hasActuation has an NGSI-LD object of type “sosa:Actuation”
§ An Entity of type “sosa:Actuation” includes information about the execution
status of the last actuation (command execution) over such Entity.
§ Extended NGSI-LD API for launching Actuations over Entities
§ POST /ngsi-ld/v1/entities/{entityId}/actuations/{command}
§ ContextSourceRegistration API to allow registration of Actuation Executors
§ The “WoT-NGSI-LD Intermediary” is actually an Actuation Executor

16. 1
5
TD with NGSI-LD IoW semantic annotations (II)
source: W3C
{
"id": "urn:dev:wot:com:example:servient:lamp",
"name": "MyLampThing",
"securityDefinitions": {
"basic_sc": {"scheme": "basic", "in":"header"}
},
"security": ["basic_sc"],
"sosa:hasFeatureOfInterest": "urn:ngsi-ld:Streetlight:Sl3456",
"properties": {
"status" : {
"@type" : "sosa:Observation",
"sosa:observedProperty": "https://uri.fiware.org/ns/dataModels/powerState",
"type": "string",
"forms": [{"href": "https://mylamp.example.com/status"}]
}
},
"actions": {
"toggle" : {
"@type" : ["sosa:Actuation", "saref:ToggleCommand"],
"sosa:actsOnProperty": "https://uri.fiware.org/ns/dataModels/powerState",
"forms": [{"href": "https://mylamp.example.com/toggle"}]
}
},
"events":{
"overheating":{
"@type" : ["sosa:Observation”, "saref:NotifyCommand”],
"sosa:observedProperty": "https://uri.fiware.org/ns/dataModels/status",
"data": {"type": "string"},
"forms": [{
"href": "https://mylamp.example.com/oh",
"subprotocol": "longpoll"
}]
}
},
"@context": [
"https://www.w3.org/2019/wot/td/v1",
{ "sosa": "http://www.w3.org/ns/sosa/" , ”saref": "https://w3id.org/saref#" }
]
}
W3C SSN Annotations
for NGSI-LD Mapping
{
"id": "urn:ngsi-ld:Streetlight:Sl3456",
"type": "Streetlight",
"powerState": "on",
"status" : ”overheating",
"hasActuation" : ["urn:ngsi-ld:sosa:Actuation:A456"],
"hasCommand" : ["saref:ToggleCommand"],
"@context": [
"https://schema.lab.fiware.org/ld/context",
"https://uri.etsi.org/ngsi-ld/v1"
]
}
{
"id": "urn:ngsi-ld:sosa:Actuation:A456",
"type": "sosa:Actuation",
"name : "toggle",
"sosa:hasResult": "OK",
"sosa:resultTime" : "2019-05-22T12:34:09Z",
"sosa:actsOnProperty" : "powerState",
"sosa:madeByActuator" : "urn:dev:wot:com:example:servient:lamp",
"sosa:hasFeatureOfInterest" : "urn:ngsi-ld:Streetlight:Sl3456",
"saref:hasCommand": "saref:ToggleCommand",
"@context": [
"https://schema.lab.fiware.org/ld/context",
"https://uri.etsi.org/ngsi-ld/v1",
{
"sosa": "http://www.w3.org/ns/sosa/",
”saref": "https://w3id.org/saref#"
}
]
}
Action Mapping
Property / Event Mapping

17. 16
NGSI-LD WoT Adaptor Detailed Architecture
NGSI-LD
Context Broker
Thing
Catalogue
WoT Thing
Thing
Descriptors
Client
Applications
NGSI-LD API
WoT Thing
WoT Things
Thing Descriptions
(Entity2Thing
)
Semantic
Annotations
(Thing2Entity
)
Semantic
Annotations
NGSI-LD
Context Source
NGSI-LD
Data Log & Writer
Property Manager Event ListenerAction Executor
Add
TD
Register
CSource
forward
Intermediary Servient
update
<<Notification>>
New TD
WoT Mapper
Log Data
Adapt NGSI-LD
Read/write
execute
listen
NGSI-LD

18. 17
Issues and open points
§ Scalability
§ How to deal with millions of TDs and related annotations?
§ TD Templates (For further study).
§ Use JSON Hyperlinked Schema?
§ An Actuation Entity per Entity and command type … could be too much?
§ Semantic annotations suitability
§ Is the usage of W3C SSN / ETSI SAREF appropriate?.
§ Are we assuming the right semantics?
§ Specific Ontology for TD annotations?
§ What happens to WoT Binding Templates?
§ How to convey data transformations?
§ What happens to IoT Agents?
§ Can IoT Agents play a role in this architecture?

19. 18
Next Steps
§ Refine the proposed Architecture through a Proof of Concept
§ Study other alternatives for semantic annotation
§ Other concepts in SSN, SAREF, or custom ontology, etc.
§ Align with latest version of W3C WoT TD Specification
§ We hope to see it in CR state soon!!
§ Contribute to ETSI deliverables on NGSI-LD IoW with W3C WoT
§ Raise awareness of this work within the W3C WoT Community

20. 19
Conclusions
§ Interworking between W3C WoT and NGSI-LD is feasible
§ Semantic annotations are a powerful tool to bridge the Information
Management Layer and the IoT Service Layer
§ W3C WoT TD specification is very promising and flexible
§ W3C WoT TD as the lingua franca for semantic description of devices in
the Smart Domain
§ A great opportunity to improve the IoT Chapter of FIWARE!!

21. 20
References
§ W3C WoT Architecture (Candidate Recommendation)
§ https://www.w3.org/TR/wot-architecture/
§ W3C WoT TD Specification (Candidate Recommendation)
§ https://www.w3.org/TR/wot-thing-description/
§ NGSI-LD Specification (January 2019)
§ https://www.etsi.org/deliver/etsi_gs/CIM/001_099/009/01.01.01_60/gs_CIM009v010101p.pdf
§ W3C WoT Binding Templates (Editor’s Draft)
§ https://w3c.github.io/wot-binding-templates/
§ ETSI SAREF Ontology
§ http://ontology.tno.nl/saref/
§ W3C SSN Ontology
§ https://www.w3.org/TR/2017/REC-vocab-ssn-20171019/

22. Thank you!
http://fiware.org
Follow @FIWARE on Twitter
José Manuel Cantera Fonseca
FIWARE Foundation
josemanuel.cantera@fiware.org