Internet DRAFT - draft-keranen-core-senml-fetch
draft-keranen-core-senml-fetch
Network Working Group A. Keranen
Internet-Draft Ericsson
Intended status: Standards Track M. Mohajer
Expires: January 25, 2019 u-blox UK
July 24, 2018
FETCH & PATCH with Sensor Measurement Lists (SenML)
draft-keranen-core-senml-fetch-02
Abstract
The Sensor Measurement Lists (SenML) media type and data model can be
used to send collections of resources, such as batches of sensor data
or configuration parameters. The CoAP iPATCH, PATCH, and FETCH
methods enable accessing and updating parts of a resource or multiple
resources with one request. This document defines semantics for the
CoAP iPATCH, and FETCH methods for resources represented with the
SenML data model.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Using FETCH and iPATCH with SenML . . . . . . . . . . . . . . 3
3.1. SenML FETCH . . . . . . . . . . . . . . . . . . . . . . . 3
3.2. SenML iPATCH . . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 5
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 5
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 6
1. Introduction
The Sensor Measurement Lists (SenML) media type [I-D.ietf-core-senml]
and data model can be used to transmit collections of resources, such
as batches of sensor data or configuration parameters.
Example of a SenML collection is shown below:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
{"n":"5750", "vs":"Ceiling light"}
]
Here three resources "3306/0/5850", "3306/0/5851", and "3306/0/5750",
of an IPSO dimmable light smart object [IPSO] are represented using a
single SenML Pack with three SenML Records. All resources share the
same base name "2001:db8::2/3306/0/", hence full names for resources
are "2001:db8::2/3306/0/5850", etc.
The CoAP [RFC7252] iPATCH and FETCH methods [RFC8132] enable
accessing and updating parts of a resource or multiple resources with
one request.
This document defines semantics for the CoAP iPATCH and FETCH methods
for resources represented with the SenML data model. Same semantics
apply also for the CoAP PATCH method.
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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 BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
Readers should also be familiar with the terms and concepts discussed
in [RFC8132] and [I-D.ietf-core-senml]. Also the following terms are
used in this document:
Fetch Record: One set of parameters that is used to match SenML
Record(s).
Fetch Pack: One or more Fetch Records in an array structure.
Presented using the SenML media type.
Patch Record: One set of parameters similar to Fetch Record but also
containing instructions on how to change existing SenML Pack(s).
Patch Pack: One or more Patch Records in an array structure.
Target Record: A Record in a SenML Pack that is matching the
selection criteria of a Fetch or Patch Record and hence is a
target for a Fetch or Patch operation.
3. Using FETCH and iPATCH with SenML
The FETCH and iPATCH methods use the same SenML media type to enable
re-use of existing SenML parsers and generators, in particular on
constrained devices.
3.1. SenML FETCH
The FETCH method can be used to select and return parts of one or
more SenML Packs. The SenML Records are selected by giving the
name(s) of the resources using the SenML "name" and/or "base name"
Fields.
For example, to select resources "5850" and "5851" from the example
in Section 1, the following Fetch Pack can be used:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850"},
{"n":"5851"}
]
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The result to a FETCH request with the example above would be:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":true},
{"n":"5851", "v":42},
]
When SenML Records contain also time values, a name may no longer
uniquely identify a single Record. When no time is given in a Fetch
Record, all SenML Records with the given name are matched. When time
is given in the Fetch Record, only a SenML Record (if any) with equal
time value and name is matched.
The resolved form of records (Section 4.6 of [I-D.ietf-core-senml])
is used when comparing the names and times of the Target and Fetch
Records to accommodate for differences in use of the base values.
3.2. SenML iPATCH
The iPATCH method can be used to change the values of SenML Records,
to add new Records, and to remove existing Records. The names and
times of the Patch Records are given and matched in same way as for
the Fetch Records, except each Patch Record can match at most one
Target Record. Patch Packs can also include new values and other
SenML Fields for the Records.
When the name in a Patch Record matches with the name in an existing
Record, the time values are compared. If the time values do not
exist or are equal in both Records, the Target Record is replaced
with the contents of the Patch Record.
If a Patch Record contains a name, or combination of a time value and
a name, that do not exist in any existing Record in the Pack, the
given Record, with all the fields it contains, is added to the Pack.
If a Patch Record has a value field with value null, the matched
Record (if any) is removed from the Pack.
For example, the following document could be given as iPATCH payload
to change/set values of two SenML Records for the example in
Section 1:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10}
]
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If the request is successful, the resulting representation of the
example SenML Pack would be as follows:
[
{"bn":"2001:db8::2/3306/0/", "n":"5850", "vb":false},
{"n":"5851", "v":10},
{"n":"5750", "vs":"Ceiling light"}
]
4. Security Considerations
The security and privacy considerations of SenML apply also with the
FETCH and iPATCH methods.
Since the the FETCH and iPATCH methods potentially allow retrieving
or changing many resources at once, particular care must be taken to
ensure that access control rules for different resources are
respected.
5. Acknowledgements
The use of FETCH and iPATCH methods with SenML was first introduced
by the OMA SpecWorks LwM2M v1.1 specification. This document
generalizes the use to any SenML representation. The authors would
like to thank Jaime Jimenez, Klaus Hartke, Carsten Bormann, and also
everyone in the IETF CoRE and OMA SpecWorks DMSE working groups for
their contributions and reviews.
6. References
6.1. Normative References
[I-D.ietf-core-senml]
Jennings, C., Shelby, Z., Arkko, J., Keranen, A., and C.
Bormann, "Sensor Measurement Lists (SenML)", draft-ietf-
core-senml-16 (work in progress), May 2018.
[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>.
[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>.
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[RFC8132] van der Stok, P., Bormann, C., and A. Sehgal, "PATCH and
FETCH Methods for the Constrained Application Protocol
(CoAP)", RFC 8132, DOI 10.17487/RFC8132, April 2017,
<https://www.rfc-editor.org/info/rfc8132>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
6.2. Informative References
[IPSO] IPSO, "IP for Smart Objects - IPSO Objects", 2018,
<https://github.com/IPSO-Alliance/pub>.
Authors' Addresses
Ari Keranen
Ericsson
Email: ari.keranen@ericsson.com
Mojan Mohajer
u-blox UK
Email: Mojan.Mohajer@u-blox.com
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