The WoT Profile Specification defines a Profiling Mechanism and a WoT Core Profile, which enables out of the box interoperability among things and devices. Out of the box interoperability implies, that devices can be integrated into various application scenarios without deep level adaptations. Typically only minor configuration operations are necessary (such as entering a network key, or IP address) to use the device in a certain scenario. These actions can be done by anyone without specific training.
The WoT Core Profile defines a set of constraints and rules, which compliant thing descriptions have to adopt to guarantee interoperability.These rules are prescriptive, to ensure that compliant implementations satisfy the semantic guarantees implied by them. We call this set of rules a Profile.
The WoT Profile Specification as defined in this document serves two purposes:
This document incudes a binding of the core data model to HTTP(S) and selected notification sub-protocols. The core data model can be bound to other protocols - it is expected that bindings to other protocols (e.g. MQTT, CoAP) will be defined in the near future.
A TD that is compliant to the core profile MUST adhere to both the constraints on the data model and the protocol binding.
Devices that constrain their use of the Thing Description to the WoT Core Profile can interoperate with each other out-of-the-box.
Note that the core profile is not exclusive. Device implementers are free to adopt
other features of the thing description that go beyond the constraints
of the core profile, however the interoperability guarantees of the core profile
hold only for the WoT Core Profile subset.
Motivation for a Profile
The W3C WoT Thing Architecture [[wot-architecture11]] and WoT Thing Description [[wot-thing-description]] define a powerful description mechanism and a format to describe myriads of very different devices, which may be connected over various protocols. The format is very flexible and open and puts very few normative requirements on devices that implement it.
However, this flexibility de-facto prevents interoperability, since, without additional rules, it allows implementers to make many choices that do not provide guarantees of common behavior between implementations.
The W3C WoT Architecture [[wot-architecture11]] and the WoT Thing Description [[wot-thing-description]] have been developed as a versatile format, that allows describing the interactions between multiple devices and protocols.
This flexibility permits an easy integration of new device types and protocols, however it risks interoperability, since there are no guarantees that two devices which are formally spec-compliant, will be able to communicate.
To increase adoption of the WoT specifications, interoperability between on premise devices, edge devices and the cloud is essential. Even if every manufacturer is implementing the current Thing Description specification in full flexibility, there is no interoperability guarantee; many choices are still left to the implementations and there are very few normative requirements that a device has to fulfill.
A Thing Description can be used in two fundamentally different deployment scenarios:
For green field deployments, where the implementations are being carried out and corresponding thing descriptions are being created, it is easier to achieve full interoperability by using a small, extensible Core Profile.
In the brown field area, due to the nature of existing deployments and protocols, a broad spectrum of variations and potentially high complexity of thing descriptions inhibits interoperability and will most likely lead to additional profiles of the WoT Thing Description and domain-specific thing consumer implementations.
The WoT Core Profile can be used by green field deployments and gives guidance to new implementers of the WoT specifications. It has already proved in brown-field scenarios in the PlugFests, where existing devices, that already existed as products, prototypes or demonstrators, were described with Thing Descriptions that are constrained to the Core Profile.
During the recent WoT PlugFests there were many de-facto agreements on the use of a small constrained subset of interaction patterns and protocol choices. These de-facto agreements select a common subset of the WoT Thing Description, based on proven interoperability among manufacturers.
The aim of this specification is to formalize these agreements by defining a WoT Core Profile based on the choices that were made by the implementers of PlugFest devices.
The WoT Core Profile contains additional normative requirements that MUST be satisfied by devices to be compliant to the profile.
Adoption of the WoT Core Profile will significantly limit the implementation burden of device and cloud implementors.
The WoT Core Profile was defined with the following main goals:
It makes choices on the required metadata fields as well as the supported interactions and protocol endpoints. It introduces some constraints on data schemas for properties and actions which are required for resource constrained devices in real-world deployments. The format does not forbid the use of additional elements of the WoT Thing Description for vendor specific extensions, however this will impact interoperability.
Devices, which implement the Core Profile, are out-of-the-box interoperable with other Core Profile compliant devices. Furthermore, the Core Profile simplifies device validation and compliance testing since a corresponding conformance test suite can be defined.
A device or consumer implementation complies with this specification if it follows the normative statements in the present document.
A JSON Schema [[?JSON-SCHEMA]] to validate the compliance of a Thing Description with the core profile is provided in Appendix .
This specification uses the same terminology as the WoT Architecture and Thing Description specifications.
For convenience of the reader, we use the terms keyword and field for the linguistic notion vocabulary term as defined in the Thing Description Specification.
We use the terms device and thing in an interchangeable manner.
In order to conform with a profile, a Web Thing MUST conform with all the normative statements in the profile's specification.
In order to denote that a given
Web Thing
conforms to one or more profiles, its Thing Description MUST include a
profile
member [[wot-thing-description11]]. The value of
the profile
member MUST be set to either a valid URI
[[RFC3986]] identifying a single profile, or an array of valid URIs
identifying multiple profiles.
{ "@context": "https://www.w3.org/2019/wot/td/v1", "id": "urn:dev:ops:32473-WoTLamp-1234", "profile": "https://www.w3.org/2022/wot/profile/core/v1", "title": "My Lamp", "description": "A web connected lamp", ... }
{ "@context": "https://www.w3.org/2019/wot/td/v1", "id": "urn:dev:ops:32473-WoTLamp-1234", "profile": [ "https://www.w3.org/2022/wot/profile/core/v1", "https://www.w3.org/2022/wot/profile/constrained/v1" ], "title": "My Lamp", "description": "A web connected lamp", ... }
The name "Core Profile" is still under discussion (see #21).
In order to denote that a given
Web Thing
conforms to the Core Profile, its Thing Description MUST have a
profile
member [[wot-thing-description]] with a value
of https://www.w3.org/2022/wot/profile/core/v1
.
This section defines a protocol binding which describes how a Consumer communicates with a Web Thing [[wot-architecture11]] using JSON [[JSON]] payloads over the HTTP [[HTTP11]] protocol.
A Consumer or Web Thing conforming to the WoT Core Profile MUST implement this protocol binding.
The examples provided throughout the Core Profile Protocol Binding section describe how a Consumer would communicate with a Web Thing which produces the following Thing Description:
{ "@context": "https://www.w3.org/2019/wot/td/v1", "id": "https://mywebthingserver.com/things/lamp", "profile": "https://www.w3.org/2022/wot/profile/core", "base": "https://mywebthingserver.com/things/lamp/", "title": "My Lamp", "description": "A web connected lamp", "securityDefinitions": { "oauth2": { "scheme": "oauth2", "flow": "code", "authorization": "https://mywebthingserver.com/oauth/authorize", "token": "https://mywebthingserver.com/oauth/token" } }, "security": "oauth2", "properties": { "on": { "type": "boolean", "title": "On/Off", "description": "Whether the lamp is turned on", "forms": [{"href": "./properties/on"}] }, "level" : { "type": "integer", "title": "Brightness", "description": "The level of light from 0-100", "unit": "percent", "minimum" : 0, "maximum" : 100, "forms": [{"href": "./properties/level"}] } }, "actions": { "fade": { "title": "Fade", "description": "Fade the lamp to a given level", "input": { "type": "object", "properties": { "level": { "type": "integer", "minimum": 0, "maximum": 100, "unit": "percent" }, "duration": { "type": "integer", "minimum": 0, "unit": "milliseconds" } } }, "forms": [{"href": "./actions/fade"}] } }, "events": { "overheated": { "title": "Overheated", "data": { "type": "number", "unit": "degree celsius" }, "description": "The lamp has exceeded its safe operating temperature", "forms": [{ "href": "./events/overheated", "subprotocol": "sse" }] } }, "forms": [ { "op": ["readallproperties", "writemultipleproperties"], "href": "./properties" }, { "op": "queryallactions", "href": "./actions" }, { "op": ["subscribeallevents", "unsubscribeallevents"], "href": "./events", "subprotocol": "sse" } ] }
The informative declarative protocol binding example in
Appendix A
illustrates how the concrete protocol binding defined in this section
would have to be represented in a Thing Description if it did not use
the profiling mechanism. In other words, if all of the defaults and
protocol specifics defined in this section were instead provided
declaratively using hypermedia
Form
s, with all defaults made explicit.
readproperty
The URL of a Property
resource to be used when reading
the value of a property MUST be obtained from a Thing Description by
locating a
Form
inside the corresponding
PropertyAffordance
for which:
op
member
contains the value readproperty
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Property
resource.
In order to read the value of a property, a Consumer MUST send an HTTP request to a Web Thing with:
GET
Property
resourceAccept
header set to application/json
GET /things/lamp/properties/on HTTP/1.1 Host: mythingserver.com Accept: application/json
If a Web Thing receives an HTTP request following the format above and the Consumer has permission to read the corresponding property, then upon successfully reading the value of the property it MUST send an HTTP response with:
200
Content-Type
header set to application/json
HTTP/1.1 200 OK Content-Type: application/json false
writeproperty
The URL of a Property
resource to be used when writing
the value of a property MUST be obtained from a Thing Description by
locating a
Form
inside the corresponding
PropertyAffordance
for which:
op
member
contains the value writeproperty
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Property
resource.
In order to write the value of a property, a Consumer MUST send an HTTP request to a Web Thing with:
PUT
Property
resourceContent-Type
header set to application/json
PUT /things/lamp/properties/on HTTP/1.1 Host: mythingserver.com Content-Type: application/json true
If a Web Thing receives an HTTP request following the format above and the Consumer has permission to write the corresponding property, then upon successfully writing the value of the property it MUST send an HTTP response with:
204
HTTP/1.1 204 No Content
observeproperty
The URL of a Property
resource to be used when
observing the value of a property MUST be obtained from a Thing
Description by locating a
Form
inside the corresponding
PropertyAffordance
for which:
op
member contains the value
observeproperty
href
member is http
or https
subprotocol
member has a value of
sse
The resolved value of the href
member MUST then be used
as the URL of the Property
resource.
In order to observe a property, a Consumer MUST follow the
Server-Sent Events [[EVENTSOURCE]] specification to open a
connection with the Web Thing at the URL of the
Property
resource.
This involves the Consumer sending an HTTP request to the Web Thing with:
GET
Property
resourceAccept
header set to text/event-stream
Connection
header set to keep-alive
GET /things/lamp/properties/level HTTP/1.1 Host: mythingserver.com Accept: text/event-stream Connection: keep-alive
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be initiated using the EventSource
constructor.
const levelSource = new EventSource('/things/lamp/properties/level');
If a Web Thing receives an HTTP request following the format above and the Consumer has permission to observe the corresponding property, then it MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to maintain an open connection with the Consumer and push a property value to the Consumer each time the value of the specified property changes.
This involves the Web Thing initially sending an HTTP response to the Consumer with:
200
Content-Type
header set to
text/event-stream
HTTP/1.1 200 OK Content-Type: text/event-stream
Whenever the value of the specified property changes while the Web
Thing has an open connection with a Consumer, the Web Thing MUST
send a property value to the Consumer using the event stream format in
the Server-Sent Events [[EVENTSOURCE]] specification. For each message
sent, the Web Thing MUST set the event
field to the
name of the PropertyAffordance
and populate the
data
field with the property value, serialized in JSON
and following the data schema specified in the
PropertyAffordance
. The id
field SHOULD be set to a unique
identifier for the property change, for use when re-establishing a
dropped connection (see below). It is RECOMMENDED that the identifier
is a timestamp representing the time at which the property changed, in
the "date-time" format specified by [[RFC3339]].
event: level\n data: 42\n id: 2021-11-17T15:33:20.827Z\n\n
If the connection between the Consumer and Web Thing drops
(except as a result of the unobserve
operation
defined below), the Consumer MUST re-establish the connection
following the steps outlined in the Server-Sent Events specification
[[EVENTSOURCE]]. Once the connection is re-established the Web Thing
SHOULD, if possible, send any missed property changes which occured
since the last change specified by the Consumer in a
Last-Event-ID
header.
unobserveproperty
In order to stop observing a property, a Consumer MUST terminate the corresponding Server-Sent Events connection with the Web Thing as specified in the Server-Sent Events specification [[EVENTSOURCE]].
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be terminated using the close()
method
on an EventSource
[[EVENTSOURCE]] object.
levelSource.close();
readallproperties
The URL of a Properties
resource to be used when
reading the value of all properties at once MUST be obtained from a
Thing Description by locating a
Form
inside the top level
forms
member
for which:
op
member contains the value
readallproperties
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Properties
resource.
In order to read the value of all properties, a Consumer MUST send an HTTP request to a Web Thing with:
GET
Properties
resource
Accept
header set to application/json
GET /things/lamp/properties HTTP/1.1 Host: mythingserver.com Accept: application/json
If a Web Thing receives an HTTP request following the format above, then upon successfully reading the values of all the readable properties to which the Consumer has permission to access, it MUST send an HTTP response with:
200
Content-Type
header set to application/json
HTTP/1.1 200 OK Content-Type: application/json { "on": false, "level": 100 }
writemultipleproperties
The URL of a Properties
resource to be used when
writing the value of multiple properties at once MUST be obtained
from a Thing Description by locating a
Form
inside the top level
forms
member
for which:
op
member contains the value
writemultipleproperties
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Properties
resource.
In order to write the value of multiple properties at once, a Consumer MUST send an HTTP request to a Web Thing with:
PUT
Properties
resource
Content-Type
header set to application/json
PUT /things/lamp/properties HTTP/1.1 Host: mythingserver.com Content-Type: application/json { "on": true, "level": 50 }
If a Web Thing receives an HTTP request following the format above, then upon successfully writing the values of the requested writable properties it MUST send an HTTP response with:
204
HTTP/1.1 204 No Content
observeallproperties
The URL of a properties resource to be used when observing changes
to all properties of a Web Thing MUST be obtained from a Thing
Description by locating a
Form
inside the top level
forms
member of a Thing Description for which:
op
member contains the value
observeallproperties
href
member is http
or https
subprotocol
member has a value of
sse
The resolved value of the href
member MUST then be used
as the URL of the properties resource.
In order to observe changes to all properties of a Web Thing, a Consumer MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to open a connection with the Web Thing at the URL of the properties resource.
This involves the Consumer sending an HTTP request to the Web Thing with:
GET
Accept
header set to text/event-stream
Connection
header set to keep-alive
GET /things/lamp/properties HTTP/1.1 Host: mythingserver.com Accept: text/event-stream Connection: keep-alive
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be initiated using the EventSource
constructor.
const lampPropertiesSource = new EventSource('/things/lamp/properties');
If a Web Thing receives an HTTP request following the format above then it MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to maintain an open connection with the Consumer and push new property values to the Consumer for all properties for which it has permission to observe.
This involves the Web Thing initially sending an HTTP response to the Consumer with:
200
Content-Type
header set to
text/event-stream
HTTP/1.1 200 OK Content-Type: text/event-stream
Whenever a property changes while the Web Thing has an open
connection with a Consumer, the Web Thing MUST send the new property
value to the Consumer using the event stream format in the
Server-Sent Events [[EVENTSOURCE]] specification. For each message
sent, the Web Thing MUST set the event
field to the
name of the PropertyAffordance
and populate the
data
field with the new property value. The
property data MUST follow the data schema specified in the
PropertyAffordance
and MUST be serialized in JSON.
The id
field SHOULD be set to a unique identifier for
the event, for use when re-establishing a dropped connection (see
below). It is RECOMMENDED that the identifier is a timestamp
representing the time at which the property changed, in the
"date-time" format specified by [[RFC3339]].
event: level\n data: 42\n id: 2021-11-17T15:33:20.827Z\n\n
If the connection between the Consumer and Web Thing drops
(except as a result of the unobserveallproperties
operation defined below), the Consumer MUST re-establish the
connection following the steps outlined in the Server-Sent Events
specification [[EVENTSOURCE]]. Once the connection is re-established
the Web Thing SHOULD, if possible, send any missed property changes
which occured since the last change specified by the Consumer in a
Last-Event-ID
header.
unobserveallproperties
In order to unobserve all properties, a Consumer MUST terminate the corresponding Server-Sent Events connection with the properties endpoint of the Web Thing, following the steps specified in the Server-Sent Events specification [[EVENTSOURCE]].
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be terminated using the close()
method
on an EventSource
[[EVENTSOURCE]] object.
lampPropertiesSource.close();
The readmultipleproperties
operation is currently
excluded due to the complexities of the request payload format and
because it doesn't add much functionality over
readproperty
and readallproperties
. The
writeallproperties
operation is currently excluded
because it is just a special case of
writemultipleproperties
.
invokeaction
The URL of an Action
resource to be used when invoking
an action MUST be obtained from a Thing Description by locating a
Form
inside the corresponding
ActionAffordance
for which:
op
member is invokeaction
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Action
resource.
In order to invoke an action on a Web Thing, a Consumer MUST send an HTTP request to the Web Thing with:
POST
Action
resourceAccept
header set to application/json
Content-Type
header set to application/json
POST /things/lamp/actions/fade HTTP/1.1 Host: mythingserver.com Content-Type: application/json Accept: application/json { "level": 100, "duration": 5 }
If a Web Thing receives an HTTP request following the format above then it MUST respond with one of three response formats:
For long-running actions which are not expected to finish executing
within the timeout period of an HTTP request (e.g. 30 to 120
seconds), it is RECOMMENDED that a Web Thing respond with an
Asynchronous Action Response so that a Consumer may continue to
monitor the status of an action request with a
queryaction
operation on a dynamically created
ActionStatus
resource, after the initial
invokeaction
response.
For short-lived actions which are expected to finish executing within the timeout period of an HTTP request, a Web Thing MAY wait until the action has completed to send a Synchronous Action Response.
If a Web Thing encounters an error in attempting to execute an
action before responding to the invokeaction
request,
then it MUST send an Error Response.
Conforming Consumers MUST support all three types of response
to the initial invokeaction
request, but
support for subsequent operations on an ActionStatus
resource is OPTIONAL.
ActionStatus
object
The status of an action invocation request is represented by an
ActionStatus
object which includes the following
members:
Member | Description | Assignment | Type |
---|---|---|---|
status |
The status of the action request. | mandatory |
string (one of pending ,
running , completed or
failed )
|
output |
The output data, if any, of a completed action which
MUST conform with the output data schema of the
corresponding
ActionAffordance .
|
optional | any type |
error |
An error message, if any, associated with a failed action
which MUST use the JSON serialization of the Problem Details
format [[RFC7807]] (only needed in response to a
queryaction
operation).
|
optional | object |
href |
The [[URL]] of an ActionStatus resource which can
be polled with a queryaction operation to get
the latest status of the action, the
URI
scheme [[RFC3986]] of which MUST resolve to
http or https (only needed for an
Asynchronous Action
Response).
|
optional | string |
timeRequested |
A timestamp indicating the time at which the Thing received the request to execute the action, in ISO format [[ISO8601-1]]. | mandatory | string |
timeEnded |
A timestamp indicating the time at which the Thing successfully completed executing the action, or failed to execute the action, in ISO format [[ISO8601-1]]. | optional | string |
If providing a Synchronous Action Response, a Web Thing MUST send an HTTP response with:
200
Content-Type
header set to
application/json
ActionStatus
object serialized
in JSONHTTP/1.1 200 OK Content-Type: application/json { "status": "completed", "timeRequested": "2021-11-10T11:43:20.135Z", "timeEnded": "2021-11-10T11:43:25.135Z" }
If providing an Asynchronous Action Response, a Web Thing MUST send
an HTTP response containing the URL of an ActionStatus
resource, the
URI
scheme [[RFC3986]] of which MUST resolve to http
or https
. The response MUST have:
201
Content-Type
header set to
application/json
Location
header set to the URL of the
ActionStatus
resource
ActionStatus
object serialized
in JSON, with its href
member set to the URL
of the ActionStatus
resource
HTTP/1.1 201 CREATED Content-Type: application/json Location: /things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655 { "status": "pending", "href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655", "timeRequested": "2021-11-10T11:43:19.135Z" }
queryaction
A queryaction
operation is used to query the current
state of an ongoing action request.
A Web Thing which provides
Asynchronous Action Responses to an invokeaction
operation on an Action
MUST also support
queryaction
operations on
that same Action
.
A Web Thing which only provides
Synchronous Action Responses to an invokeaction
operation on an Action
SHOULD NOT support
queryaction
operations on that same
Action
.
The URL of an ActionStatus
resource to be used in a
queryaction
operation MUST be obtained from the
Location
header of an
Asynchronous Action Response, or the href
member of
the ActionStatus
object in its body.
In order to query the status of an action request, a Consumer MUST send an HTTP request to a Web Thing with:
GET
ActionStatus
resource
Accept
header set to application/json
GET /things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655 Host: mythingserver.com Accept: application/json
If a Web Thing receives an HTTP request following the format
above and the Consumer has permission to query the corresponding
ActionStatus
resource, then upon successfully reading
the status of the action request it MUST send an HTTP response
with:
200
Content-Type
header set to application/json
ActionStatus
object
representing the current status of the action request, serialized
in JSONHTTP/1.1 200 OK Content-Type: application/json { "status": "running", "timeRequested": "2021-11-10T11:43:19.135Z" }
If the queried action failed to execute, then the
status
member of the ActionStatus
object
MUST be set to "failed"
and the error
member may optionally provide additional error information
conforming to the Problem Details format [[RFC7807]].
HTTP/1.1 200 OK Content-Type: application/json { "status": "failed", "error": { "type": "https://mythingserver.com/docs/errors/invalid-level", "title": "Invalid value for level provided", "invalid-params": [ { "name": "level", "reason": "Must be a valid number between 0 and 100" } ] }, "timeRequested": "2021-11-10T11:43:19.135Z", "timeEnded": "2021-11-10T11:43:20.513Z" }
cancelaction
A cancelaction
operation is used to cancel an ongoing
Action
request.
A Web Thing which provides
Asynchronous Action Responses to an invokeaction
operation on an Action
MAY also support
cancelaction
operations on
that same Action
.
A Web Thing which only provides
Synchronous Action Responses to an invokeaction
operation on an Action
SHOULD NOT support
cancelaction
operations on that same
Action
.
The URL of an ActionStatus
resource to be used in a
cancelaction
operation MUST be obtained from the
Location
header of an
Asynchronous Action Response, or the href
member of
the ActionStatus
object in its body.
In order to cancel an action request, a Consumer MUST send an HTTP request to a Web Thing with:
DELETE
ActionStatus
resource
DELETE /things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655 HTTP/1.1 Host: mythingserver.com
If a Web Thing receives an HTTP request following the format
above and the Consumer has permission to cancel the corresponding
Action
request, then upon successfully cancelling
Action
it MUST send an HTTP response with:
204
HTTP/1.1 204 No Content
queryallactions
The URL of an Actions
resource to be used when
querying the status of all ongoing action requests MUST be obtained
from a Thing Description by locating a
Form
inside the top level
forms
member
for which:
op
member contains the value
queryallactions
href
member is http
or https
The resolved value of the href
member MUST then be used
as the URL of the Actions
resource.
In order to query the status of all ongoing action requests, a Consumer MUST send an HTTP request to a Web Thing with:
GET
Actions
resource
Accept
header set to application/json
GET /things/lamp/actions HTTP/1.1 Host: mythingserver.com Accept: application/json
If a Web Thing receives an HTTP request following the format above, then upon successfully retreiving the status of all ongoing action requests to which the Consumer has permission to access, it MUST send an HTTP response with:
200
Content-Type
header set to application/json
Action
name,
with the value of each object member being an array of
ActionStatus
objects
representing the action requests, serialized in JSON. Each array
MUST be sorted in reverse chronological order such that the
most recent action request appears first.
HTTP/1.1 200 OK Content-Type: application/json { "fade": [ { "status": "completed", "href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655", "timeRequested": "2021-11-10T11:43:19.135Z", "timeEnded": "2021-11-10T11:43:20.513Z" }, { "status": "failed", "href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a456-558329", "timeRequested": "2021-11-10T11:42:15.133Z", "timeEnded": "2021-11-10T11:42:22.524Z" }, { "status": "running", "href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a457-434656", "timeRequested": "2021-11-10T11:41:53.351Z" }, { "status": "pending", "href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a457-ea9519", "timeRequested": "2021-11-10T11:39:53.651Z" } ] }
Action
request is cancelled with a
cancelaction
operation, its ActionStatus
object is deleted and need not be retained. For all other
Action
requests it is assumed that a Web Thing will
store the ActionStatus
object so that its status may
later be queried with a queryaction
or
queryallactions
operation. It is not expected that
ActionStatus
objects should be retained indefinitely,
they may be stored in volatile memory and/or periodically pruned.
The length of time for which to retain ActionStatus
objects is expected to be implementation-specific and may depend on
application-specific requirements or resource constraints.
The Core Profile uses Server-Sent Events [[EVENTSOURCE]] as a mechanism for Consumers to subscribe to events emitted by a Web Thing.
Consumers are not required to implement the
EventSource
JavaScript API from the Server-Sent Events
specification in order to conform with this profile. Any programming
language may be used to consume an event stream.
subscribeevent
The URL of an Event
resource to be used when
subscribing to an event MUST be obtained from a Thing Description
by locating a
Form
inside the corresponding
EventAffordance
for which:
op
member
contains the value subscribeevent
href
member is http
or https
subprotocol
member has a value of
sse
The resolved value of the href
member MUST then be used
as the URL of the Event
resource.
In order to subscribe to an event, a Consumer MUST follow the
Server-Sent Events [[EVENTSOURCE]] specification to open a
connection with the Web Thing at the URL of the Event
resource.
This involves the Consumer sending an HTTP request to the Web Thing with:
GET
Event
resourceAccept
header set to text/event-stream
Connection
header set to keep-alive
GET /things/lamp/events/overheated HTTP/1.1 Host: mythingserver.com Accept: text/event-stream Connection: keep-alive
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be initiated using the EventSource
constructor.
const overheatedEventSource = new EventSource('/things/lamp/events/overheated');
If a Web Thing receives an HTTP request following the format above and the Consumer has permission to subscribe to the corresponding event, then it MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to maintain an open connection with the Consumer and push event data to the Consumer as events of the specified type are emitted.
This involves the Web Thing initially sending an HTTP response to the Consumer with:
200
Content-Type
header set to
text/event-stream
HTTP/1.1 200 OK Content-Type: text/event-stream
Whenever an event of the specified type occurs while the Web Thing
has an open connection with a Consumer, the Web Thing MUST
send event data to the Consumer using the event stream format in the
Server-Sent Events [[EVENTSOURCE]] specification. For each message
sent, the Web Thing MUST set the event
field to the
name of the EventAffordance
and populate the
data
field with event data, if any. The
event data MUST follow the data schema specified in the
EventAffordance
and MUST be serialized in JSON.
The id
field SHOULD be set to a unique identifier for
the event, for use when re-establishing a dropped connection (see
below). It is RECOMMENDED that the identifier is a timestamp
representing the time at which the event occurred, in the
"date-time" format specified by [[RFC3339]].
event: overheated\n data: 90\n id: 2021-11-16T16:53:50.817Z\n\n
If the connection between the Consumer and Web Thing drops
(except as a result of the unsubscribe
operation
defined below), the Consumer MUST re-establish the connection
following the steps outlined in the Server-Sent Events specification
[[EVENTSOURCE]]. Once the connection is re-established the Web Thing
SHOULD, if possible, send any missed events which occured since
the last event specified by the Consumer in a
Last-Event-ID
header.
unsubscribeevent
In order to unsubscribe from an event, a Consumer MUST terminate the corresponding Server-Sent Events connection with the Web Thing as specified in the Server-Sent Events specification [[EVENTSOURCE]].
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be terminated using the close()
method
on an EventSource
[[EVENTSOURCE]] object.
overheatedEventSource.close();
subscribeallevents
The URL of an events resource to be used when subscribing to all
events emitted by a Web Thing MUST be obtained from a Thing
Description by locating a
Form
inside the top level
forms
member of a Thing Description for which:
op
member contains the value
subscribeallevents
href
member is http
or https
subprotocol
member has a value of
sse
The resolved value of the href
member MUST then be used
as the URL of the events resource.
In order to subscribe to all events emitted by a Web Thing, a Consumer MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to open a connection with the Web Thing at the URL of the events resource.
This involves the Consumer sending an HTTP request to the Web Thing with:
GET
Accept
header set to text/event-stream
Connection
header set to keep-alive
GET /things/lamp/events HTTP/1.1 Host: mythingserver.com Accept: text/event-stream Connection: keep-alive
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be initiated using the EventSource
constructor.
const lampEventsSource = new EventSource('/things/lamp/events');
If a Web Thing receives an HTTP request following the format above then it MUST follow the Server-Sent Events [[EVENTSOURCE]] specification to maintain an open connection with the Consumer and push event data to the Consumer for all event types for which it has permission to subscribe.
This involves the Web Thing initially sending an HTTP response to the Consumer with:
200
Content-Type
header set to
text/event-stream
HTTP/1.1 200 OK Content-Type: text/event-stream
Whenever an event occurs while the Web Thing has an open connection
with a Consumer, the Web Thing MUST send event data to the Consumer
using the event stream format in the Server-Sent Events
[[EVENTSOURCE]] specification. For each message sent, the Web Thing
MUST set the event
field to the
name of the EventAffordance
and populate the
data
field with event data, if any. The
event data MUST follow the data schema specified in the
EventAffordance
and MUST be serialized in JSON.
The id
field SHOULD be set to a unique identifier for
the event, for use when re-establishing a dropped connection (see
below).
event: overheated\n data: 90\n id: 2021-11-16T16:53:50.817Z\n\n
If the connection between the Consumer and Web Thing drops
(except as a result of the unsubscribeallevents
operation defined below), the Consumer MUST re-establish the
connection following the steps outlined in the Server-Sent Events
specification [[EVENTSOURCE]]. Once the connection is re-established
the Web Thing SHOULD, if possible, send any missed events which
occured since the last event specified by the Consumer in a
Last-Event-ID
header.
unsubscribeallevents
In order to unsubscribe from all events, a Consumer MUST terminate the corresponding Server-Sent Events connection with the events endpoint of the Web Thing, following the steps specified in the Server-Sent Events specification [[EVENTSOURCE]].
For Consumers implemented in JavaScript [[ECMASCRIPT]] and executed
in a runtime which exposes the
EventSource
interface, a Server-Sent Events
connection can be terminated using the close()
method
on an EventSource
[[EVENTSOURCE]] object.
lampEventsSource.close();
If any of the operations defined above are unsuccessful then the Web Thing MUST send an HTTP response with an HTTP error code which describes the reason for the failure. It is RECOMMENDED that error responses use one of the following HTTP error codes:
400 Bad Request
401 Unauthorized
403 Forbidden
404 Not Found
500 Internal Server Error
Web Things MAY respond with other valid HTTP error codes
(e.g. 418 I'm a teapot
),
but Consumers MAY interpret those error codes as a generic 4xx
or 5xx
error with no special defined behaviour.
If we define the finite set of error responses as above then we should also define what a Consumer should do if it receives a 3xx redirect type response.
If an HTTP error response contains a body, the content of that body MUST conform with with the Problem Details format [[RFC7807]].
Below is a list of security schemes [[wot-thing-description]] which conformant Web Things MAY use and conformant Consumers MUST support:
The list of security schemes to include in the Core Profile is still under discussion.
A Thing MAY implement multiple security schemes.
Security schemes MUST be applied using the top level security
member of a
Thing
and MUST NOT be applied to individual
Form
s.
Please see WoT Security Best Practices for implementation advice.
In order to a conform with the Core Profile, a Web Thing's Thing Description [[wot-thing-description]] MUST be retrievable from a URL [[URL]] using the HTTP protocol [[HTTP11]], to enable its discovery using a Direct Introduction Mechanism [[wot-discovery]].
In order to a conform with the Core Profile, a Consumer MUST be able to retrieve a Thing Description when provided with its HTTP URL.
A Thing Description can be syntactically validated with the JSON Schema [[?JSON-SCHEMA]] for compliance with the core profile.
Todo: Define a JSON-SCHEMA.
The following informative Thing Description illustrates how the concrete
protocol binding defined in the Core Profile
would have to be represented by the Web Thing described by
EXAMPLE 3 if it did not use the
profiling mechanism. In other words, if
all of the defaults and protocol specifics defined in the Core Profile
protocol binding were instead provided
declaratively using hypermedia
Form
s, with all defaults made explicit.
This example is only intended as an illustration of how Web Things conforming to the Core Profile can benefit from more concise Thing Descriptions. A Web Thing which does use the profiling mechanism would only need to use the significantly more concise form shown in EXAMPLE 3 in order to provide the same information.
{ "@context": "https://www.w3.org/2019/wot/td/v1", "id": "https://mywebthingserver.com/things/lamp", "base": "https://mywebthingserver.com/things/lamp/", "title": "My Lamp", "description": "A web connected lamp", "securityDefinitions": { "oauth2": { "scheme": "oauth2", "flow": "code", "authorization": "https://mywebthingserver.com/oauth/authorize", "token": "https://mywebthingserver.com/oauth/token" } }, "security": "oauth2", "properties": { "on": { "type": "boolean", "title": "On/Off", "description": "Whether the lamp is turned on", "forms": [ { "op": "readproperty", "href": "./properties/on", "htv:methodName": "GET", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "htv:statusCodeNumber": 200, "contentType": "application/json" } }, { "op": "writeproperty", "href": "./properties/on", "htv:methodName": "PUT", "contentType": "application/json", "response": { "htv:statusCodeNumber": 204 } } ] }, "level" : { "type": "integer", "title": "Brightness", "description": "The level of light from 0-100", "unit": "percent", "minimum" : 0, "maximum" : 100, "forms": [ { "op": "readproperty", "href": "./properties/level", "htv:methodName": "GET", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "htv:statusCodeNumber": 200, "contentType": "application/json" } }, { "op": "writeproperty", "href": "./properties/level", "htv:methodName": "PUT", "contentType": "application/json", "response": { "htv:statusCodeNumber": 204 } } ] } }, "actions": { "fade": { "title": "Fade", "description": "Fade the lamp to a given level", "input": { "type": "object", "properties": { "level": { "type": "integer", "minimum": 0, "maximum": 100, "unit": "percent" }, "duration": { "type": "integer", "minimum": 0, "unit": "milliseconds" } } }, "forms": [ { "op": "invokeaction", "href": "./actions/fade", "htv:methodName": "POST", "contentType": "application/json", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "htv:statusCodeNumber": 201, "htv:headers": [ { "htv:fieldName": "Location", "htv:fieldValue": "/fade/{id}" } ], "contentType": "application/json", "schema": "actionStatus" }, "additionalResponses": [ { "htv:statusCodeNumber": 200, "htv:headers": [ { "htv:fieldName": "Location", "htv:fieldValue": "/fade/{id}" } ], "contentType": "application/json", "schema": "actionStatus" } ] }, { "op": "queryaction", "href": "./actions/fade/{id}", "htv:methodName": "GET", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "contentType": "application/json", "schema": "actionStatus" } }, { "op": "cancelaction", "href": "./actions/fade/{id}", "htv:methodName": "DELETE", "contentType": "application/json" } ], "uriVariables": { "id": { "type": "string", "description": "identifier of action request" } } } }, "events": { "overheated": { "title": "Overheated", "data": { "type": "number", "unit": "degree celsius" }, "description": "The lamp has exceeded its safe operating temperature", "forms": [ { "op": "subscribeevent", "href": "./events/overheated", "subprotocol": "sse", "htv:methodName": "GET", "htv:headers": [ { "htv:fieldName": "Accept", "htv:fieldValue": "text/event-stream" }, { "htv:fieldName": "Connection", "htv:fieldValue": "keep-alive" } ], "response": { "htv:statusCodeNumber": 200, "contentType": "text/event-stream" } }, { "op": "unbsubscribeevent", "href": "./events/overheated", "subprotocol": "sse" } ] } }, "forms": [ { "op": "readallproperties", "href": "./properties", "htv:methodName": "GET", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "htv:statusCodeNumber": 200, "contentType": "application/json" } }, { "op": "writemultipleproperties", "href": "./properties", "htv:methodName": "PUT", "contentType": "application/json", "response": { "htv:statusCodeNumber": 204 } }, { "op": "queryallactions", "href": "./actions", "htv:methodName": "GET", "htv:headers": [{ "htv:fieldName": "Accept", "htv:fieldValue": "application/json" }], "response": { "contentType": "application/json", "schema": "actionStatusList" } }, { "op": "subscribeallevents", "href": "./events", "subprotocol": "sse", "htv:methodName": "GET", "htv:headers": [ { "htv:fieldName": "Accept", "htv:fieldValue": "text/event-stream" }, { "htv:fieldName": "Connection", "htv:fieldValue": "keep-alive" } ], "response": { "htv:statusCodeNumber": 200, "contentType": "text/event-stream" } }, { "op": "unsubscribeallevents", "href": "./events", "subprotocol": "sse" } ], "schemaDefinitions": { "actionStatus": { "type": "object", "properties": { "status": { "type": "string", "enum": [ "pending", "running", "completed", "failed" ] }, "error": { "type": "object" }, "href": { "type": "string", "format": "uri", "const": "./actions/fade/{id}" } }, "required": [ "status" ] }, "actionStatusList": { "type": "object", "additionalProperties": { "type": "array", "items": { "type": "object", "properties": { "status": { "type": "string", "enum": [ "pending", "running", "completed", "failed" ] }, "error": { "type": "object" }, "href": { "type": "string", "format": "uri", "const": "./actions/fade/{id}" } }, "required": [ "status" ] } } } } }