Internet DRAFT - draft-ietf-core-interfaces
draft-ietf-core-interfaces
CoRE Working Group Z. Shelby
Internet-Draft ARM
Intended status: Informational M. Koster
Expires: September 12, 2019 SmartThings
C. Groves
J. Zhu
Huawei
B. Silverajan, Ed.
Tampere University
March 11, 2019
Reusable Interface Definitions for Constrained RESTful Environments
draft-ietf-core-interfaces-14
Abstract
This document defines a set of Constrained RESTful Environments
(CoRE) Link Format Interface Descriptions [RFC6690] applicable for
use in constrained environments. These include the: Actuator,
Parameter, Read-only parameter, Sensor, Batch, Linked Batch and Link
List interfaces.
The Batch, Linked Batch and Link List interfaces make use of resource
collections. This document further describes how collections relate
to interfaces.
Many applications require a set of interface descriptions in order
provide the required functionality. This document defines an
Interface Description attribute value to describe resources
conforming to a particular interface.
Editor's notes:
o The git repository for the draft is found at https://github.com/
core-wg/interfaces
Status of This Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at https://datatracker.ietf.org/drafts/current/.
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Internet-Drafts are draft documents valid for a maximum of six months
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This Internet-Draft will expire on September 12, 2019.
Copyright Notice
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document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Collections . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Introduction to Collections . . . . . . . . . . . . . . . 5
3.2. Use Cases for Collections . . . . . . . . . . . . . . . . 5
3.3. Collection Types . . . . . . . . . . . . . . . . . . . . 6
3.4. Content-Formats for Collections . . . . . . . . . . . . . 6
3.5. Link Embedding . . . . . . . . . . . . . . . . . . . . . 7
3.6. Links and Items in Collections . . . . . . . . . . . . . 7
3.7. Queries on Collections . . . . . . . . . . . . . . . . . 8
3.8. Observing Collections . . . . . . . . . . . . . . . . . . 8
4. Interface Descriptions . . . . . . . . . . . . . . . . . . . 9
4.1. Link List . . . . . . . . . . . . . . . . . . . . . . . . 11
4.2. Batch . . . . . . . . . . . . . . . . . . . . . . . . . . 11
4.3. Linked Batch . . . . . . . . . . . . . . . . . . . . . . 12
4.4. Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 13
4.5. Parameter . . . . . . . . . . . . . . . . . . . . . . . . 14
4.6. Read-only Parameter . . . . . . . . . . . . . . . . . . . 14
4.7. Actuator . . . . . . . . . . . . . . . . . . . . . . . . 14
5. Security Considerations . . . . . . . . . . . . . . . . . . . 15
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
6.1. Link List . . . . . . . . . . . . . . . . . . . . . . . . 15
6.2. Batch . . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.3. Linked Batch . . . . . . . . . . . . . . . . . . . . . . 16
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6.4. Sensor . . . . . . . . . . . . . . . . . . . . . . . . . 16
6.5. Parameter . . . . . . . . . . . . . . . . . . . . . . . . 17
6.6. Read-only parameter . . . . . . . . . . . . . . . . . . . 17
6.7. Actuator . . . . . . . . . . . . . . . . . . . . . . . . 17
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 17
8. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 18
9. Changelog . . . . . . . . . . . . . . . . . . . . . . . . . . 18
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 22
10.1. Normative References . . . . . . . . . . . . . . . . . . 22
10.2. Informative References . . . . . . . . . . . . . . . . . 22
Appendix A. Current Usage of Interfaces . . . . . . . . . . . . 23
A.1. Constrained RESTful Environments (CoRE) Link Format
(IETF) . . . . . . . . . . . . . . . . . . . . . . . . . 23
A.2. Open Connectivity Foundation (OCF) . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 24
1. Introduction
IETF Standards for machine to machine communication in constrained
environments describe a REST protocol and a set of related
information standards that may be used to represent machine data and
machine metadata in REST interfaces. CoRE Link-format is a standard
for doing Web Linking [RFC8288] in constrained environments. SenML
[RFC8428] is a simple data model and representation format for
composite and complex structured resources. CoRE Link-Format and
SenML can be used by CoAP [RFC7252] or HTTP servers.
The discovery of resources offered by a constrained server is very
important in machine-to-machine applications where there are no
humans in the loop. Machine application clients must be able to
adapt to different resource organizations without advance knowledge
of the specific data structures hosted by each connected thing. The
use of Web Linking for the description and discovery of resources
hosted by constrained origin servers is specified by CoRE Link Format
[RFC6690]. CoRE Link Format additionally defines a link attribute
for interface description ("if") that can be used to describe the
REST interface of a resource, and may include a link to a description
document.
This document defines a set of Link Format interface descriptions for
some common design patterns that enable the server side composition
and organization, and client side discovery and consumption, of
machine resources using Web Linking. A client discovering the "if"
link attribute will be able to consume resources based on its
knowledge of the expected interface types. In this sense the
Interface Type acts in a similar way as a Content-Format, but as a
selector for a high level functional abstraction.
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An interface description describes a resource in terms of its
associated content formats, data types, URI templates, REST methods,
parameters, and responses. Basic interface descriptions are defined
for sensors, and actuators.
A set of collection types is defined for organizing resources for
discovery, and for various forms of bulk interaction with resource
sets using typed embedding links.
This document first defines the concept of collection interface
descriptions. It then defines a number of generic interface
descriptions that may be used in contrained environments. Several of
these interface descriptions utilise collections.
Whilst this document assumes the use of CoAP [RFC7252], the REST
interfaces described can also be realized using HTTP [RFC7230].
2. Terminology
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
This document requires readers to be familiar with all the terms and
concepts that are discussed in [RFC8288] and [RFC6690]. This
document makes use of the following additional terminology:
Gradual Reveal: A REST design where resources are discovered
progressively using Web Linking.
Interface Description: The Interface Description describes the
generic REST interface to interact with a resource or a set of
resources. Its use is described via the Interface Description
'if' attribute which is an opaque string used to provide a name or
URI indicating a specific interface definition used to interact
with the target resource. One can think of this as describing
verbs usable on a resource.
Resource Discovery: The process allowing a client to identify
resources being hosted on an origin server.
3. Collections
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3.1. Introduction to Collections
A Collection is a resource which represents one or more related
resources. [RFC6573] describes the "item" and "collection" Link
Relation. An "item" link relation identifies a member of collection.
A "collection" indicates the collection that an item is a member of.
For example, a collection might be a resource representing a catalog
of products, while an item is a resource related to an individual
product.
Section 1.2.2/[RFC6690] also describes resource collections.
This document uses the concept of "collection" and applies it to
interface descriptions. A collection interface description consists
of a set of links and a set of items pointed to by the links which
may be sub-resources of the collection resource. The collection
interface descriptions described in this document are Link List,
Batch and Linked Batch.
The links in a collection are represented in CoRE Link-Format
Content-Formats including JSON and CBOR variants, and the items in
the collection may be represented by SenML, including JSON and CBOR
variants. In general, a collection may support items of any
available Content-Format.
A particular resource item may be a member of more than one
collection at a time by being linked to, but may only be a
subresource of one collection.
Some collections may have pre-configured items and links, and some
collections may support dynamic creation and removal of items and
links. Likewise, modification of items in some collections may be
permitted, and not in others.
Links in collections may be selected for processing by a particular
request by using Query Filtering as described in CoRE Link-Format
[RFC6690].
3.2. Use Cases for Collections
Collections may be used to provide gradual reveal of resources on an
endpoint. There may be a small set of links at the .well-known/core
location, which may in turn point to other collections of resources
that represent device information, device configuration, device
management, and various functional clusters of resources on the
device.
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A collection may be used to group a set of like resources for bulk
state update or actuation. For example, the brightness control
resources of a number of luminaries may be grouped by linking to them
in a collection. The collection type may support receiving a single
update from a client and sending that update to each resource item in
the collection.
Items may be sub-resources of the collection resource. This enables
updates to multiple items in the collection to be processed together
within the context of the collection resource.
3.3. Collection Types
There are three collection types defined in this document:
+-----------------+---------+
| Collection Type | if= |
+-----------------+---------+
| Link List | core.ll |
| | |
| Batch | core.b |
| | |
| Linked Batch | core.lb |
+-----------------+---------+
Table 1: Collection Type Summary
The interface description defined in this document offer a deeper
explanation of the methods that may be applied to the three
collections.
3.4. Content-Formats for Collections
The collection interfaces can use the CoRE Link-Format for the link
representations and SenML or text/plain for representations of items.
The examples given are for collections that expose resources and
links in these formats.
The choice of whether to return a representation of the links or of
the items or of the collection format is determined by the Accept
header option in the request. Likewise, the choice of updating link
metadata or item data or the collection resource itself is determined
by the Content-Format option in the header of the update request
operation.
The default Content-Formats for collection types described in this
document are:
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Links: application/link-format, application/link-format+json
Items: application/senml+json, text/plain
3.5. Link Embedding
Collections may provide resource encapsulation by supporting link
embedding. Link embedding may be used to provide a single resource
with which a client may interact to obtain a set of related resource
values. This is analogous to an image tag (link) causing the image
to display inline in a browser window. Link embedding enables the
bulk processing of items in the collection using a single operation
targeting the collection resource. Performing a GET on a collection
resource may return a single representation containing all of the
embedded linked resources. For example, a collection for
manufacturer parameters may consist of manufacturer name, date of
manufacture, location of manufacture, and serial number resources
which can be read as a single SenML data object.
A subset of resources in the collection may be selected for operation
using Query Filtering. Bulk Read operations using GET return a SenML
representation of all selected resources. Bulk item Update
operations using PUT or POST apply the payload document to all
selected resource items in the collection. A Batch update is
performed by applying the resource values in the payload document to
all resources in the collection that match any resource name in the
payload document.
3.6. Links and Items in Collections
Links use CoRE Link-Format representation by default and may point to
any resource reachable from the context of the collection. This
includes links to resources with absolute paths as well as links that
point to other network locations, if the context of the collection
allows. Links to sub-resources in the collection MUST have a path-
element starting with the resource name, as per [RFC3986]. Links to
resources in the global context MUST start with a root path
identifier [RFC8288]. Links to other collections are formed per
[RFC3986].
Examples of links:
</sen/>;if="core.lb": Link to the /sen/ collection describing it as
a core.lb type collection (Linked Batch)
</sen/temp>;rt="temperature": A link to the temp resource with an
absolute path.
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<temp>;rt="temperature": Link to the temp subresource of the
collection in which this link appears.
<temp>;anchor="/sen/": A link to the temp subresource of the
collection /sen/ which is assumed not to be a subresource of the
collection in which the link appears, but is expected to be
identified in the collection by resource name.
Links in the collection MAY be Read, Updated, Added, or Removed using
the CoRE Link-Format or JSON Merge-Patch Content-Formats on the
collection resource. Reading links uses the GET method and returns
an array or list containing the link-values of all selected links.
Links may be added to the collection using POST or PATCH methods.
Updates to links MUST use the PATCH method and MAY use query
filtering to select links for updating. The PATCH method on links
MUST use the JSON Merge-Patch Content-Format (application/merge-
patch+json) specified in [RFC7396].
Items in the collection SHOULD be represented using the SenML
(application/senml+json) or plain text (text/plain) Content-Formats,
depending on whether the representation is of a single data point or
multiple data points. Items MAY be represented using any supported
Content-Format.
3.7. Queries on Collections
Collections MAY support query filtering as defined in CoRE Link-
Format [RFC6690]. Operations targeting either the links or the items
MAY select a subset of links and items in the collection by using
query filtering. The Content-Format specified in the request header
selects whether links or items are targeted by the operation.
3.8. Observing Collections
Resource Observation via [I-D.ietf-core-dynlink] using CoAP [RFC7252]
MAY be supported on items in a collection. A subset of the
conditional observe parameters MAY be specified to apply. In most
cases pmin and pmax are useful. Resource observation on a
collection's resource returns the collection representation.
Observation Responses, or notifications, SHOULD provide the
collection representations in SenML Content-Format. Notifications
MAY include multiple observations of the collection resource, with
SenML time stamps indicating the observation times.
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4. Interface Descriptions
This section defines REST interfaces for Sensor, Parameter, Read-Only
Paramter and Actuator resource types, in addition to the Link List,
Batch and Linked Batch collection types. Each type is described
along with its Interface Description attribute value, valid methods
and content formats. These are shown for each interface in the table
below.
The if= column defines the Interface Description (if=) attribute
value to be used in the CoRE Link Format for a resource conforming to
that interface. When this value appears in the if= attribute of a
link, the resource MUST support the corresponding REST interface
described in this section. The resource MAY support additional
functionality, which is out of scope for this document. Although
these interface descriptions are intended to be used with the CoRE
Link Format, they are applicable for use in any REST interface
definition.
The Methods column defines the methods supported by that interface,
which are described in more detail below.
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+--------------+---------+-----------------+--------------------+
| Interface | if= | Methods | Content-Formats |
+--------------+---------+-----------------+--------------------+
| Link List | core.ll | GET | link-format |
| | | | |
| Batch | core.b | GET, PUT, POST | senml |
| | | | |
| Linked Batch | core.lb | GET, PUT, POST, | link-format, senml |
| | | | |
| | | DELETE | |
| | | | |
| Sensor | core.s | GET | senml, |
| | | | |
| | | | text/plain |
| | | | |
| Parameter | core.p | GET, PUT | senml, |
| | | | |
| | | | text/plain |
| | | | |
| Read-only | core.rp | GET | senml, |
| | | | |
| Parameter | | | text/plain |
| | | | |
| Actuator | core.a | GET, PUT, POST | senml, |
| | | | |
| | | | text/plain |
+--------------+---------+-----------------+--------------------+
Table 2: Interface Description Summary
The following is an example of links in the CoRE Link Format using
these interface descriptions.
Req: GET /.well-known/core
Res: 2.05 Content (application/link-format)
</s/>;rt="simple.sen";if="core.b",
</s/light>;rt="simple.sen.lt";if="core.s",
</s/temp>;rt="simple.sen.tmp";if="core.s";obs,
</s/humidity>;rt="simple.sen.hum";if="core.s",
</a/>;rt="simple.act";if="core.b",
</a/1/led>;rt="simple.act.led";if="core.a",
</a/2/led>;rt="simple.act.led";if="core.a",
</d/>;rt="simple.dev";if="core.ll",
</l/>;if="core.lb"
Figure 1: Binding Interface Example
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4.1. Link List
Link List is the base interface to provide gradual reveal of
resources on a CoRE origin server. It is used to retrieve (GET) a
list of resources on an origin server. The GET request SHOULD
contain an Accept option with the application/link-format content
format. However if the resource does not support any other form of
content-format the Accept option MAY be elided.
Note: The use of an Accept option with application/link-format is
recommended even though it is not strictly needed for the Link List
interface because this interface is extended by the batch and linked
batch interfaces where different content-formats are possible.
The request returns a list of URI references with absolute paths to
the resources as defined in CoRE Link Format. This interface is
typically used with a parent resource to enumerate sub-resources but
may be used to reference any resource on an origin server.
The following example interacts with a Link List /d/ containing
Parameter sub-resources /d/name, /d/model.
Req: GET /d/ (Accept:application/link-format)
Res: 2.05 Content (application/link-format)
</d/name>;rt="simple.dev.n";if="core.p",
</d/model>;rt="simple.dev.mdl";if="core.rp"
4.2. Batch
The Batch interface is used to manipulate a collection of sub-
resources at the same time. The Batch interface description supports
the same methods as its sub-resources, and can be used to read (GET),
update (PUT) or apply (POST) the values of those sub-resource with a
single resource representation. The sub-resources of a Batch MAY be
heterogeneous. Hence, a method used on the Batch only applies to
sub-resources that support it. For example Sensor interfaces do not
support PUT, and thus a PUT request to a Sensor member of that Batch
would be ignored. A batch requires the use of SenML Media types in
order to support multiple sub-resources.
The following example interacts with a Batch /s/ with Sensor sub-
resources /s/light, /s/temp and /s/humidity.
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Req: GET /s/
Res: 2.05 Content (application/senml+json)
[
{ "bn": "example.com/s/" },
{ "n": "light", "v": 123, "u": "lx" },
{ "n": "temp", "v": 27.2, "u": "Cel" },
{ "n": "humidity", "v": 80, "u": "%RH" }
]
4.3. Linked Batch
The Linked Batch interface is an extension of the Batch interface.
Contrary to the basic Batch which is a collection statically defined
by the origin server, a Linked Batch is dynamically controlled by a
client. A Linked Batch resource has no sub-resources. Instead the
resources forming the batch are referenced using Web Linking
[RFC8288] and the CoRE Link Format [RFC6690]. A request with a POST
method and a content format of application/link-format simply appends
new resource links to the collection. The links in the payload MUST
reference a resource on the origin server with an absolute path. A
DELETE request removes the entire collection. All other requests
available for a basic Batch are still valid for a Linked Batch.
The following example interacts with a Linked Batch /l/ and creates a
collection containing /s/light, /s/temp and /s/humidity in 2 steps.
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Req: POST /l/ (Content-Format: application/link-format)
</s/light>,</s/temp>
Res: 2.04 Changed
Req: GET /l/
Res: 2.05 Content (application/senml+json)
[
{ "bn": "example.com/" },
{ "n": "/s/light", "v": 123, "u": "lx" },
{ "n": "/s/temp", "v": 27.2, "u": "Cel" }
]
Req: POST /l/ (Content-Format: application/link-format)
</s/humidity>
Res: 2.04 Changed
Req: GET /l/ (Accept: application/link-format)
Res: 2.05 Content (application/link-format)
</s/light>,</s/temp>,</s/humidity>
Req: GET /l/
Res: 2.05 Content (application/senml+json)
[
{ "bn": "example.com/" },
{ "n": "/s/light", "v": 123, "u": "lx" },
{ "n": "/s/temp", "v": 27.2, "u": "Cel" },
{ "n": "/s/humidity", "v": 80, "u": "%RH" }
]
Req: DELETE /l/
Res: 2.02 Deleted
4.4. Sensor
The Sensor interface allows the value of a sensor resource to be read
(GET). The Media type of the resource can be either plain text or
SenML. Plain text MAY be used for a single measurement that does not
require meta-data. For a measurement with meta-data such as a unit
or time stamp, SenML SHOULD be used. A resource with this interface
MAY use SenML to return multiple measurements in the same
representation, for example a list of recent measurements.
The following are examples of Sensor interface requests in both text/
plain and application/senml+json.
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Req: GET /s/humidity (Accept: text/plain)
Res: 2.05 Content (text/plain)
80
Req: GET /s/humidity (Accept: application/senml+json)
Res: 2.05 Content (application/senml+json)
[
{ "bn": "example.com/s/" },
{ "n": "humidity", "v": 80, "u": "%RH" }
]
4.5. Parameter
The Parameter interface allows configurable parameters and other
information to be modeled as a resource. The value of the parameter
can be read (GET) or update (PUT). Plain text or SenML Media types
MAY be returned from this type of interface.
The following example shows request for reading and updating a
parameter.
Req: GET /d/name
Res: 2.05 Content (text/plain)
node5
Req: PUT /d/name (text/plain)
outdoor
Res: 2.04 Changed
4.6. Read-only Parameter
The Read-only Parameter interface allows configuration parameters to
be read (GET) but not updated. Plain text or SenML Media types MAY
be returned from this type of interface.
The following example shows request for reading such a parameter.
Req: GET /d/model
Res: 2.05 Content (text/plain)
SuperNode200
4.7. Actuator
The Actuator interface is used by resources that model different
kinds of actuators (changing its value has an effect on its
environment). Examples of actuators include for example LEDs,
relays, motor controllers and light dimmers. The current value of
the actuator can be read (GET) or the actuator value can be updated
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(PUT). In addition, this interface allows the use of POST to change
the state of an actuator, for example to toggle between its possible
values. Plain text or SenML Media types MAY be returned from this
type of interface. A resource with this interface MAY use SenML to
include multiple measurements in the same representation, for example
a list of recent actuator values or a list of values to updated.
The following example shows requests for reading, setting and
toggling an actuator (turning on a LED).
Req: GET /a/1/led
Res: 2.05 Content (text/plain)
0
Req: PUT /a/1/led (text/plain)
1
Res: 2.04 Changed
Req: POST /a/1/led (text/plain)
Res: 2.04 Changed
Req: GET /a/1/led
Res: 2.05 Content (text/plain)
0
5. Security Considerations
An implementation of a client needs to be prepared to deal with
responses to a request that differ from what is specified in this
document. A server implementing what the client thinks is a resource
with one of these interface descriptions could return malformed
representations and response codes either by accident or maliciously.
A server sending maliciously malformed responses could attempt to
take advantage of a poorly implemented client for example to crash
the node or perform denial of service. Conversely, a malicious
client could attempt to write to arbitrary resources on a poorly
implemented server described in a linked batch.
6. IANA Considerations
This document registers the following CoRE Interface Description
(if=) Link Target Attribute Values.
6.1. Link List
Attribute Value: core.ll
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Description: The Link List interface is used to retrieve a list of
resources on an origin server.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
6.2. Batch
Attribute Value: core.b
Description: The Batch interface is used to manipulate a collection
of sub-resources at the same time.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
6.3. Linked Batch
Attribute Value: core.lb
Description: The Linked Batch interface is an extension of the Batch
interface. Contrary to the basic Batch which is a collection
statically defined by the origin server, a Linked Batch is
dynamically controlled by a client.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
6.4. Sensor
Attribute Value: core.s
Description: The Sensor interface allows the value of a sensor
resource to be read.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
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6.5. Parameter
Attribute Value: core.p
Description: The Parameter interface allows configurable parameters
and other information to be modeled as a resource. The value of
the parameter can be read or update.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
6.6. Read-only parameter
Attribute Value: core.rp
Description: The Read-only Parameter interface allows configuration
parameters to be read but not updated.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
6.7. Actuator
Attribute Value: core.a
Description: The Actuator interface is used by resources that model
different kinds of actuators (changing its value has an effect on
its environment). Examples of actuators include LEDs, relays,
motor controllers and light dimmers. The current value of the
actuator can be read or the actuator value can be updated. In
addition, this interface allows the use of POST to change the
state of an actuator, for example to toggle between its possible
values.
Reference: This document. Note to RFC Editor - please insert the
appropriate RFC reference.
Notes: None
7. Acknowledgements
Acknowledgement is given to colleagues from the SENSEI project who
were critical in the initial development of the well-known REST
interface concept, to members of the IPSO Alliance where further
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requirements for interface descriptions have been discussed, and to
Szymon Sasin, Cedric Chauvenet, Daniel Gavelle and Carsten Bormann
who have provided useful discussion and input to the concepts in this
document. Ari Keraenen provided updated SenML examples. Christian
Amsuss supplied a comprehensive review of draft -12.
8. Contributors
Matthieu Vial
Schneider-Electric
Grenoble
France
Phone: +33 (0)47657 6522
EMail: matthieu.vial@schneider-electric.com
9. Changelog
Changes from -13 to -14:
o Version update, with changes in editor's contact information
Changes from -12 to -13:
o SenML examples now use the Base Name (bn) labels from RFC 8428
o Security considerations discusses client misuse of linked batches
Changes from -11 to -12:
o Removed all text referring to function sets/profiles
o Clarified list collections
o Content-formats for collections and items rectified
o Simplified Appendix A and removed Appendix B
Changes from -10 to -11:
o Added a new Section 3.4 for Link Embedding
o Updated examples in Section 3.5
o Removed "Service Discovery" from Terminologies
o Removed discussion of function sets
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Changes from -09 to -10:
o Section 1: Amendments to remove discussing properties. *
o New author and editor added.
Changes from -08 to -09:
o Section 3.6: Modified to indicate that the entire collection
resource is returned.
o General: Added editor's note with open issues.
Changes from -07 to -08:
o Section 3.3: Modified Accepts to Accept header option.
o Addressed the editor's note in Section 4.1 to clarify the use of
the Accept option.
Changes from -06 to -07:
o Corrected Figure 1 sub-resource names e.g. tmp to temp and hum to
humidity.
o Addressed the editor's note in Section 4.2.
o Removed section on function sets and profiles as agreed to at the
IETF#97.
Changes from -05 to -06:
o Updated the abstract.
o Section 1: Updated introduction.
o Section 2: Alphabetised the order
o Section 2: Removed the collections definition in favour of the
complete definition in the collections section.
o Removed section 3 on interfaces in favour of an updated definition
in section 1.3.
o General: Changed interface type to interface description as that
is the term defined in RFC6690.
o Removed section on future interfaces.
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o Section 8: Updated IANA considerations.
o Added Appendix A to discuss current state of the art wrt to
collections, function sets etc.
Changes from -04 to -05:
o Removed Link Bindings and Observe attributes. This functionality
is now contained in I-D.ietf-core-dynlink.
o Hypermedia collections have been removed. This is covered in a
new T2TRG draft.
o The WADL description has been removed.
o Fixed minor typos.
o Updated references.
Changes from -03 to -04:
o Fixed tickets #385 and #386.
o Changed abstract and into to better describe content.
o Focus on Interface and not function set/profiles in intro.
o Changed references from draft-core-observe to RFC7641.
o Moved Function sets and Profiles to section after Interfaces.
o Moved Observe Attributes to the Link Binding section.
o Add a Collection section to describe the collection types.
o Add the Hypermedia Collection Interface Description.
Changes from -02 to -03:
o Added lt and gt to binding format section.
o Added pmin and pmax observe parameters to Observation Attributes.
o Changed the definition of lt and gt to limit crossing.
o Added definitions for getattr and setattr to WADL.
o Added getattr and setattr to observable interfaces.
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o Removed query parameters from Observe definition.
o Added observe-cancel definition to WADL and to observable
interfaces.
Changes from -01 to -02:
o Updated the date and version, fixed references.
o "Removed pmin and pmax observe parameters "[Ticket #336]"."
Changes from -00 to WG Document -01
o Improvements to the Function Set section.
Changes from -05 to WG Document -00
o Updated the date and version.
Changes from -04 to -05
o Made the Observation control parameters to be treated as resources
rather than Observe query parameters. Added Less Than and Greater
Than parameters.
Changes from -03 to -04
o Draft refresh
Changes from -02 to -03
o Added Bindings
o Updated all rt= and if= for the new Link Format IANA rules
Changes from -01 to -02
o Defined a Function Set and its guidelines.
o Added the Link List interface.
o Added the Linked Batch interface.
o Improved the WADL interface definition.
o Added a simple profile example.
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10. References
10.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
[RFC6690] Shelby, Z., "Constrained RESTful Environments (CoRE) Link
Format", RFC 6690, DOI 10.17487/RFC6690, August 2012,
<https://www.rfc-editor.org/info/rfc6690>.
[RFC8288] Nottingham, M., "Web Linking", RFC 8288,
DOI 10.17487/RFC8288, October 2017,
<https://www.rfc-editor.org/info/rfc8288>.
10.2. Informative References
[I-D.ietf-core-dynlink]
Shelby, Z., Koster, M., Groves, C., Zhu, J., and B.
Silverajan, "Dynamic Resource Linking for Constrained
RESTful Environments", draft-ietf-core-dynlink-08 (work in
progress), March 2019.
[I-D.ietf-core-resource-directory]
Shelby, Z., Koster, M., Bormann, C., Stok, P., and C.
Amsuess, "CoRE Resource Directory", draft-ietf-core-
resource-directory-19 (work in progress), January 2019.
[OIC-Core]
"OIC Resource Type Specification v1.1.0", 2016,
<https://openconnectivity.org/resources/specifications>.
[OIC-SmartHome]
"OIC Smart Home Device Specification v1.1.0", 2016,
<https://openconnectivity.org/resources/specifications>.
[OMA-TS-LWM2M]
"Lightweight Machine to Machine Technical Specification",
2016, <http://technical.openmobilealliance.org/Technical/
technical-information/release-program/current-releases/
oma-lightweightm2m-v1-0>.
[oneM2MTS0008]
"TS 0008 v1.3.2 CoAP Protocol Binding", 2016,
<http://www.onem2m.org/technical/published-documents>.
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[oneM2MTS0023]
"TS 0023 v2.0.0 Home Appliances Information Model and
Mapping", 2016,
<http://www.onem2m.org/technical/published-documents>.
[RFC3986] Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
Resource Identifier (URI): Generic Syntax", STD 66,
RFC 3986, DOI 10.17487/RFC3986, January 2005,
<https://www.rfc-editor.org/info/rfc3986>.
[RFC6573] Amundsen, M., "The Item and Collection Link Relations",
RFC 6573, DOI 10.17487/RFC6573, April 2012,
<https://www.rfc-editor.org/info/rfc6573>.
[RFC7230] Fielding, R., Ed. and J. Reschke, Ed., "Hypertext Transfer
Protocol (HTTP/1.1): Message Syntax and Routing",
RFC 7230, DOI 10.17487/RFC7230, June 2014,
<https://www.rfc-editor.org/info/rfc7230>.
[RFC7252] Shelby, Z., Hartke, K., and C. Bormann, "The Constrained
Application Protocol (CoAP)", RFC 7252,
DOI 10.17487/RFC7252, June 2014,
<https://www.rfc-editor.org/info/rfc7252>.
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/info/rfc7396>.
[RFC8428] Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
Bormann, "Sensor Measurement Lists (SenML)", RFC 8428,
DOI 10.17487/RFC8428, August 2018,
<https://www.rfc-editor.org/info/rfc8428>.
Appendix A. Current Usage of Interfaces
Editor's note: This appendix will be removed. It is only included
for information.
This appendix analyses the current landscape with regards the
definition and use of collections and interfaces. This should be
considered when considering the scope of this document.
A.1. Constrained RESTful Environments (CoRE) Link Format (IETF)
[RFC6690] assumes that different deployments or application domains
will define the appropriate REST Interface Descriptions along with
Resource Types to make discovery meaningful. It highlights that
collections are often used for these interfaces.
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Whilst 3.2/[RFC6690] defines a new Interface Description 'if'
attribute the procedures around it are about the naming of the
interface not what information should be included in the
documentation about the interface.
A.2. Open Connectivity Foundation (OCF)
The OIC Core Specification [OIC-Core] most closely aligns with the
work in this specification. It makes use of interface descriptions
as per [RFC6690] and has registered several interface identifiers
(https://www.iana.org/assignments/core-parameters/core-
parameters.xhtml#if-link-target-att-value). These interface
descriptors are similar to those defined in this specification. From
a high level perspective:
links list: OCF (oic.if.ll) -> IETF (core.ll)
Note: it's called "link list" in the IETF.
linked batch: OCF (oic.if.b) -> IETF (core.lb)
read-only: OCF (oic.if.r) -> IETF (core.rp)
read-write: OCF (oic.if.rw) -> IETF (core.p)
actuator: OCF (oic.if.a) -> IETF (core.a)
sensor: OCF (oic.if.s) -> IETF (core.s)
batch: No OCF equivalent -> IETF (core.b)
Some of the OCF interfaces make use of collections.
The OIC Core specification does not use the concept of function sets.
It does however discuss the concept of profiles. The OCF defines two
sets of documents. The core specification documents such as
[OIC-Core] and vertical profile specification documents which provide
specific information for specific applications. The OIC Smart Home
Device Specification [OIC-SmartHome] is one such specification. It
provides information on the resource model, discovery and data types.
Authors' Addresses
Zach Shelby
ARM
Kidekuja 2
Vuokatti 88600
FINLAND
Phone: +358407796297
Email: zach.shelby@arm.com
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Michael Koster
SmartThings
665 Clyde Avenue
Mountain View 94043
USA
Email: michael.koster@smartthings.com
Christian Groves
Australia
Email: cngroves.std@gmail.com
Jintao Zhu
Huawei
No.127 Jinye Road, Huawei Base, High-Tech Development District
Xi'an, Shaanxi Province
China
Email: jintao.zhu@huawei.com
Bilhanan Silverajan (editor)
Tampere University
Kalevantie 4
Tampere FI-33100
Finland
Email: bilhanan.silverajan@tuni.fi
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