Copyright © 2020-2021 W3C® (MIT, ERCIM, Keio, Beihang). W3C liability, trademark and permissive document license rules apply.
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.
The W3C WoT Thing Architecture [wot-architecture] 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.
This section describes the status of this document at the time of its publication. Other documents may supersede this document. A list of current W3C publications and the latest revision of this technical report can be found in the W3C technical reports index at https://www.w3.org/TR/.
This document was published by the Web of Things Working Group as an Editor's Draft.
Comments regarding this document are welcome. Please send them to public-wot-wg@w3.org (subscribe, archives).
Publication as an Editor's Draft does not imply endorsement by the W3C Membership.
This is a draft document and may be updated, replaced or obsoleted by other documents at any time. It is inappropriate to cite this document as other than work in progress.
This document was produced by a group operating under the 1 August 2017 W3C Patent Policy. W3C maintains a public list of any patent disclosures made in connection with the deliverables of the group; that page also includes instructions for disclosing a patent. An individual who has actual knowledge of a patent which the individual believes contains Essential Claim(s) must disclose the information in accordance with section 6 of the W3C Patent Policy.
This document is governed by the 15 September 2020 W3C Process Document.
The W3C WoT Architecture [wot-architecture] 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.
As well as sections marked as non-normative, all authoring guidelines, diagrams, examples, and notes in this specification are non-normative. Everything else in this specification is normative.
The key words MAY, MUST, MUST NOT, NOT RECOMMENDED, OPTIONAL, RECOMMENDED, SHOULD, and SHOULD NOT in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
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 § 5.5 JSON Schema of the Core Profile.
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-description]. 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/2021/wot/profile/core",
"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/2021/wot/profile/core",
"https://www.w3.org/2021/wot/profile/constrained"
],
"title": "My Lamp",
"description": "A web connected lamp",
...
}The core data model incorporates the data model defined by chapter 5 of the Thing Description specification. The normative rules defined by that data model are the baseline for the definition of the core data model and are normative for the core data model. A core profile compliant implementation MUST additionally satisfy the requirements of this chapter.
The following rules are applicable to multiple classes of the WoT Thing Description Specification, as they provide clearer semantics, improved readability and simplified processing on resource constrained devices.
One of the primary benefits of the WoT Thing Description over a typical IoT format is the additional documentation for a human reader.
Therefore, the fields
title
and
description
are MANDATORY for Things, Property Affordances,
Action Affordances, Event Affordances and Data
Schemas.
It is possible to have empty values for these fields, if, for specific purposes it is not desired to provide documentation, however this is NOT RECOMMENDED and the conscious decision is obvious from the TD.
All date and time values MUST use the canonical dateTime representation format defined in section 3.2.7 of [xmlschema-2].
As described by this section the following constraints must be observed:All dateTime values MUST use UTC as the time zone and use the 'Z' identifier.
A time value of 24:00 is NOT PERMITTED, the value 00:00 MUST be used instead.
The length of
id
,
description
and
descriptions
values is limited to 512 characters.
The length of
title
and
titles
values is limited to 64 characters.
Where a type permits using an
array of string
or a
string
, an
array of string
MUST be used.
TODO: decide if multiple types and contexts are required.
In this case the following section could be added:
The only exception to this rule are @context and @type annotations,
where both string or array of string MAY be used.
Where a type permits using an
array of DataSchema
or a
DataSchema
, an
array of DataSchema
MUST be used.
All elements of an
enum
MUST be either
string
or
number
.
Different types in a single
enum
are NOT PERMITTED.
To provide minimum interoperability, the following metadata fields of a Thing MUST be contained in a compliant Thing Description:
| keyword | type | remarks |
|---|---|---|
| title | string | human readable documentation |
| id | urn_type | a globally unique urn of the thing |
| description | string | human readable documentation |
| created | date | human readable documentation |
| modified | date | human readable documentation |
| support | urn_type | human readable documentation |
| security | array of string | simplified handling |
| version | VersionInfo | clear versioning, easy to compare different TDs |
It is RECOMMENDED to use the value "" for strings, where the value cannot be determined.
If a Thing Description is used solely within a company, the email address of the developer SHOULD be used in the support field, if the Thing Description is provided externally, a support email address SHOULD be used.
It will be evaluated whether the profile also recommends some new TD terms that may be introduced in TD 1.1. Currently the following terms are discussed: serialNumber, hardwareRevision, softwareRevision, loc_latitude, loc_longitude loc_altitude, loc_height, and loc_depth. If these, or some of them, are defined in the TD 1.1 model, they may be recommended here in one of the next draft updates.
Data Schemas are used for the values of Properties, Action input and output parameters and Event message payloads. The value of a Data Schema can be a simple type (boolean, integer, number, string) or an instance of a structured type (array and object).
The Core Data Model applies the following constraints and rules to theDataSchema
class of section 5.3.2.1 of the WoT Thing Description
Specification.
This section defines a subset of the class
DataSchema
that can be processed on resource-constrained
devices.
The Core Data Model restricts the use of
arrays and objects to the top level
of Data Schemas, i.e. only a one-level hierarchy is
permitted.
The members of a top level
object
or
array
MUST NOT be array or object types.
This may appear as a severe limitation, however it is motivated by integrating with multiple cloud services. Many enterprise services and applications are based on (relational) databases, where individual property values are stored. Of course databases can also store objects (e.g. encoded as a JSON string), however this will prevent processing by other enterprise applications.
If a property conceptually has a deeper structure, such as grid of lamps with RGB colors, the structure can be represented in the keyword of the property, i.e. lamp1_color_r, lamp1_color_g and lamp1_color_b. A similar mapping can be done for arrays and hierarchical objects. This constraint leads to simpler Thing Descriptions that can be handled by very limited devices.
The following fields MUST be contained in a DataSchema:
| keyword | type | constraints |
|---|---|---|
| description | human readable description | |
| type | string | one of boolean, integer, number, string, array or object |
The values
object
,
array MAY only be used at the top level of a Data Schema.
The type value MUST NOT be null .
PropertyAffordance
class of section 5.3.1.3 of the WoT Thing Description Specification.
The following property fields MUST be contained
in the
properties
element of a Profile compliant TD:
| keyword | type | constraints |
|---|---|---|
| title | string | unique name among all properties |
| description | string | human readable description |
| type | string |
one of boolean ,
string ,
number , integer
, object or
array . The type value
null MUST NOT be used.
|
The Thing Description permits arbitrary
object depths for properties. Parsing of a
deeply nested structure is not possible on
resource constrained devices.
Therefore each
property MUST NOT exceed a maximum depth
of 5 levels of nested
array
or
object
elements. It is RECOMMENDED to keep the nesting
of these elements below 4.
The following additional constraints MUST be applied to the Property Affordances of a Thing Description conforming to the Core Profile:
| keyword | type | constraint |
|---|---|---|
| const | anyType | MUST NOT be used |
| enum | array of simple type | Values of enums MAY only be simple types. Handling of any type is too complex to implement on resource constrained devices |
| forms | array of Forms |
The Array of Form
of each property MUST contain only a
single endpoint for each
operation readproperty
, writeproperty , observeproperty
, unobserveproperty.
|
| format | string |
If the field format
is used, only formats defined in
section 7.3.1-7.3.6 of
[JSON-SCHEMA] MAY be used.
|
| oneOf | string |
The DataSchema field oneOf
does not make sense for properties
and MUST NOT be used.
|
| uriVariables | Map of DataSchema |
uriVariables MUST NOT be used.
|
It is highly RECOMMENDED to always specify a
unit
, if a value has a metric.
Authors of Thing Descriptions should be aware, that units
that are common in their geographic region are
not globally applicable and may lead to
misinterpretation with drastic consequences.
The field
unit
could be used for non-decimal numeric types as
well, e.g. a string value with binary or hex
data (
0xCAFEBABE
,
0b01000010
), where the unit is
hex
or
bin
,
to indicate how the value should be
interpreted. It is strongly RECOMMENDED to use
the values
hex
,
oct
or
bin
in this case to achieve interoperability.
ActionAffordance
class of section 5.3.1.4 of the WoT Thing Description Specification.
The following fields MUST be contained in an action element of an Core Profile compliant TD:
| keyword | type | constraints |
|---|---|---|
| title | string | unique name among all actions |
| input | array of DataSchema | all elements of the subclasses objectSchema and dataSchema MUST only contain simple types. |
| output | array of DataSchema | all elements of the subclasses objectSchema and dataSchema MUST only contain simple types. |
The elements of the DataSchema subclasses
ArraySchema and ObjectSchema for the fields
input
and
output
are restricted to simple types in a Thing
Description conforming to the Core
Data Model. Without this limitation a higher
implementation burden would be put on resource
constrained devices (arbitrary cascaded arrays
and multi-level objects) which cannot be
satisfied by all consuming devices.
The following additional constraints MUST be applied to the Interaction Affordances of a Thing Description conforming to the Core Data Model:
| keyword | type | constraint |
|---|---|---|
| forms | array of Forms |
The Array of Form
of each action MUST contain only a single
endpoint.
|
| format | string |
If the field format
is used, only formats defined in
section 7.3.1-7.3.6 of
[JSON-SCHEMA] MAY be used.
|
| oneOf | string |
The DataSchema field oneOf
does not make sense for properties
and MUST NOT be used.
|
| uriVariables | Map of DataSchema |
uriVariables MUST NOT be used.
|
TODO:
- no optional parameters
- timeout
EventAffordance
class of section 5.3.1.5 of the WoT Thing Description Specification.
A Thing may provide more than one event mechanism to enable a variety of consumers.
TODO:
The events section needs to be signifcantly extended and define addtional constraints to ensure OOTBI. LongPoll, WebSockets and WebHooks can be considered as initial candidates for supported protocols for the event mechanism to identify appropriate data model constraints.
The individual protocol constraints need to be defined in a respective protocol binding chapter after they have been identified/evaluated in plugfests.
The following fields MUST be present in an event element of a Core TD:
| keyword | type | constraints |
|---|---|---|
| title | string | unique name among all events |
| description | string | human readable description |
| data | set of DataSchema instances in a JSON object | only the DataSchema subclasses booleanSchema, IntegerSchema, NumberSchema, StringSchema are permitted |
The following additional constraints MUST be applied to the Event Affordances of a WoT Thing Description conforming to the profile:
| keyword | type | constraint |
|---|---|---|
| forms | array of Forms |
The Array of Form
of each event MUST contain only a single
endpoint.
|
| uriVariables | Map of DataSchema |
uriVariables MUST NOT be used.
|
A Thing may provide more than one event mechanism to enable a variety of consumers.
The following fields MUST be present in a form element of a Core TD:
| keyword | type | constraints |
|---|---|---|
| title | string | unique name among all events |
| description | string | human readable description |
| data | set of DataSchema instances in a JSON object | only the DataSchema subclasses booleanSchema, IntegerSchema, NumberSchema, StringSchema are permitted |
The following additional constraints MUST be applied to the Form elements of a WoT Thing Description conforming to the Core profile:
| keyword | type | constraint |
|---|---|---|
| security | string or Array of string |
security at form
level MUST NOT be used.
|
| scopes | string or Array of string |
scopes MUST NOT be
used.
|
The "type" relationship as defined in chapter 6 of [RFC6903] is reserved for indicating an instance relationship between a thing and a thing template. The Core Data Model does not put additional constraints or requirements on links. The interpretation of a link is out of scope.
The Core Data Model defines a subset of the security schemes that MAY be implemented on resource constrained devices. A security scheme MUST be defined at the thing level. The security scheme is applied to the thing as a whole, a thing may adopt multiple security schemes.
The set of security schemes supported in the Core Data Model is based on the PlugFest results. To ensure interoperability, a TD consumer, which compliant with the Core Data Model MUST support all of the following security schemes:
When using the "no security" or "Basic Auth" security schemes it is strongly recommended to use transport layer encryption.
This section defines a protocol binding which describes how a Consumer communicates with a Web Thing [wot-architecture] 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.
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:
GETProperty resourceAccept header set to application/json
GET /things/lamp/properties/on HTTP/1.1
Host: mythingserver.com
Accept: application/jsonIf 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:
200Content-Type header set to application/json
HTTP/1.1 200 OK
Content-Type: application/json
falsewriteproperty
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:
PUTProperty resourceAccept header set to application/json
Content-Type header set to application/json
PUT /things/lamp/properties/on HTTP/1.1
Host: mythingserver.com
Content-Type: application/json
Accept: application/json
trueIf 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:
204HTTP/1.1 204 No Contentreadallproperties
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:
GETProperties resource
Accept header set to application/json
GET /things/lamp/properties HTTP/1.1
Host: mythingserver.com
Accept: application/jsonIf 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:
200Content-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:
PUTProperties resource
Content-Type header set to application/json
Accept header set to application/json
PUT /things/lamp/properties HTTP/1.1
Host: mythingserver.com
Content-Type: application/json
Accept: 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:
204HTTP/1.1 204 No Content
Other operations under consideration include
observeproperty, unobserveproperty,
observeallproperties and
unobserveallproperties.
These operations would require consesus on a default observe mechanism for HTTP (e.g. Server Sent Events or WebSockets).
readmultipleproperties is currently excluded due to
the complexities of the request payload format and because it
doesn't add much functionality over readproperty and
readallproperties.
writeallproperties 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:
POSTAction 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 conform with 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 |
If providing a Synchronous Action Response, a Web Thing MUST send an HTTP response with:
200Content-Type header set to
application/jsonActionStatus object serialized
in JSONHTTP/1.1 200 OK
Content-Type: application/json
{
"status": "completed"
}
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:
201Content-Type header set to
application/jsonLocation 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"
}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:
GETActionStatus 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:
200Content-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"
}
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",
}
]
}
}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:
DELETEActionStatus 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:
204HTTP/1.1 204 No Contentqueryallactions
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:
GETActions resource
Accept header set to application/json
GET /things/lamp/actions HTTP/1.1
Host: mythingserver.com
Accept: application/jsonIf 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:
200Content-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.
HTTP/1.1 200 OK
Content-Type: application/json
{
"fade": [
{
"status": "completed",
"href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a456-426655"
},
{
"status": "failed",
"href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a456-558329",
},
{
"status": "running",
"href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a457-434656"
},
{
"status": "pending",
"href": "/things/lamp/actions/fade/123e4567-e89b-12d3-a457-ea9519"
}
]
}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:
GETEvent 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:
200Content-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).
event: overheated\n
data: 90\n
id: 12345\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.
unsubscribeeventIn 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:
GETAccept 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:
200Content-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: 12345\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.
unsubscribealleventsIn 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 Request401 Unauthorized403 Forbidden404 Not Found500 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].
The default representation is JSON. Semantic annotations based on JSON-LD MAY be present but are not required to perform all interactions with the thing instance.
A canonical representation serves multiple purposes. It is simplifying the parsing process, enables to identify equivalent TDs by simple string comparisons. Furthermore it allows the use of a simple signing mechanism, such as Linked Data Proofs or JSON Web Signatures [RFC7515] and enables identity checks on encrypted TDs.
The canonical JSON representation format of a TD adopts the JSON Canonicalization Scheme (JCS) defined by 6292.
A Thing Description can be syntactically validated with the JSON Schema [JSON-SCHEMA] for compliance with the core profile.
Todo: Define a JSON-SCHEMA.
Referenced in:
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