Semantic Definition Format (SDF) for API translation
draft-ramos-asdf-api-translation-01
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| Document | Type | Active Internet-Draft (individual) | |
|---|---|---|---|
| Author | Edgar Ramos | ||
| Last updated | 2025-09-09 | ||
| Replaces | draft-ramos-sdf-api-translation | ||
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| Intended RFC status | (None) | ||
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draft-ramos-asdf-api-translation-01
ASDF Working Group E. Ramos
Internet-Draft Ericsson
Intended status: Standards Track 9 September 2025
Expires: 13 March 2026
Semantic Definition Format (SDF) for API translation
draft-ramos-asdf-api-translation-01
Abstract
This document defines an extension to the Semantic Definition Format
(SDF) that enables API translation between applications and devices.
The translation enables clarification of complex syntax for a service
or device to utilize a different API from the one that was first
designed to use.
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
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and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on 13 March 2026.
Copyright Notice
Copyright (c) 2025 IETF Trust and the persons identified as the
document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal
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Please review these documents carefully, as they describe your rights
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provided without warranty as described in the Revised BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. Discoverable API interfaces . . . . . . . . . . . . . . . . . 3
3. Inputting parameters to the API . . . . . . . . . . . . . . . 6
4. Methods on the API calls . . . . . . . . . . . . . . . . . . 8
5. Matching API to application logic . . . . . . . . . . . . . . 10
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
6.1. Media Type . . . . . . . . . . . . . . . . . . . . . . . 10
7. Security Considerations . . . . . . . . . . . . . . . . . . . 11
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 11
9.1. Normative References . . . . . . . . . . . . . . . . . . 11
9.2. Informative References . . . . . . . . . . . . . . . . . 11
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
In many cases, a service needed by an application can be provided
through APIs by several suppliers. Semantic matching can be used to
map the needs of the applications and adapt API calls to what the
service suppliers could provide. The main purpose of this document
is to describe methods that enable the translation of one device or
application API to another equivalent API, utilizing syntax
understandable by the deploying party.
An API translator from the original API to the updated one or even
mapping to a new service would allow an automatic adaptation to the
target API. Also, it would enable the possibility to adapt to
multiple APIs with the same data model, enabling the deployment of
services from multiple sources. This feature enables use cases such
as the usage of the cheapest or most robust service, deployment of
national services when traveling, and execution of device services
even from a different ecosystem origin.
This document provides enabling elements for communication from
devices or applications belonging to different ecosystems that do not
share the same semantic modelling. Utilizing SDF syntax enhanced
with an API format depiction, it is possible to provide an API
description that is understandable with the syntax known by the
device or application, if such semantics are defined in their data
model. The final result uses a navigable description of the API's
functions to provide the necessary information that is required by a
device application to map external required services, their
parameters, and results to an application logic using ontologically
defined objects that can be matched to remote calls in another device
application, for example.
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The API requires a mapping in applications functions by matching
syntax in addition to the actual discovery of the API; therefore, the
importance of the translation to an understandable model. This
matching could be enabled by several mechanisms described, and it is
dynamically adjusted to every new interface faced. Using SDF in
conjunction with the given schema allows an automated way to match
functionality to application intents.
┌──────────────────────┐ ┌──────────────────────┐
│ │ │ │
│ Service platform │ │ Service platform │
│ #1 │ │ #2 │
│ │ │ │
│ ┌──────────────┐ │ ┌──────────────┐
│ │ Service API ┼──┐ │ │ Service API │
└───────└─────▲────────┘ │ └───────└─────▲──┬─────┘
│ │ │ │
│ │ ┌───────────┐ │ │
│ ▼───┐ │ SDF-API │ │ │
└───────────┤ │ │TRANSLATION│ │ │
│ ┼─────► MODEL ├───────┘ │
│ ◄─────┐ ◄──────────┘
└───┘ └───────────┘
Device
*Example of a device using the API translation model to access the
same service in a different platform with a different API*
1.1. Terminology
The definitions of [I-D.ietf-asdf-sdf] apply.
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document is to be interpreted as described in
[BCP14] (RFC2119) (RFC8174) when, and only when, they appear in all
capitals, as shown here.
2. Discoverable API interfaces
A device or application may expose its capabilities as an API list.
This could be acquired in real-time by calling a command that
provides such a list of commands. For example, the resource “.well-
known/commands” [RFC8615] could be used as a specific way to request
all the commands available. The reply then includes a list of the
different API supported calls, which would be called in a
hierarchical way from the root domain that is provided by the device,
an application, or a mediating platform. The reply would contain a
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description of the supported API with a semantic definition attached.
Using the Semantic Definition Format (SDF), a reply for two commands
may include what is given in the following example:
{
"namespace": {
"name": "Relevant_URL_or_namespace_used_as_semantic_reference_(example)",
"rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns",
"demo": "https://example.com/iss-demo-setup/#",
},
"defaultNamespace": "demo",
"sdfObject": {
"target_object": {
"sdfProperty": {
"target_property": {
"description": "possible description of the property",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"demo:Output"
]
}
},
"contentFormat": "application/typeofcontent-info"
}
},
"sdfAction": {
"Name_of_the_command_1": {
"description": "Description of the command and input required",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": "demo:command1"
}
},
"sdfInputData": {
"type": "object",
"properties": {
"input_1_required": {
"description": "Description of what element is needed as first input",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"demo:input1" ]
}
},
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"type": "number",
"sdfChoice": {
"input_2_required": {
"description": "A number needed as an input of the command",
"const":"0",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"demo":"input2",
]
}
}
}
}
}
}
},
"sdfOutputData": {
"contentFormat": "application/typeofcontent-info"
}
},
"Name_of_the_command_2": {
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": "demo:command2"
}
},
"sdfInputData": {
"description": "Description of input required for second command",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": "demo:secondInput"
}
},
"type": "typeoftheinput",
"contentFormat": "application/typeofinput-info"
}
}
}
}
}
}
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In this example, one service is defined with a command1, which
requires an input1 (an object) and input2 (a number). The other
service requires a different call (command2), which requires only one
input (secondInput).
Further interaction capabilities can be included either in the
initial response, as shown above in the "sdfAction" block, or could
be discovered by further requests. For example, the descriptions of
the two actions detailed above show if they require input, what the
details of such input and the output are, and if there is additional
information related to the nature of the output. Also, the
description field could be tailor-made to provide a URI to a
vocabulary that is understandable by the device or application. In
this way, the device or application could make sense of the possible
options, parameters, and actions that the command provides or
requires.
3. Inputting parameters to the API
Once the available function calls and input parameters required by
the API have been provisioned to the requester device or application,
it can make calls to the API when required by its application logic.
The application would map the “need for a capability” to the concrete
capability provided by the provider application or device through
matching the syntax and data model. The functions are then mapped to
the calls that the application can handle and has defined syntax.
The parts of the API that are not understood by the requester device
are normally ignored. The mapping semantics from a target device or
application may be communicated to the application of the requesting
device using an SDF mapping extension draft [bormann-mapping]. In
such mapping, the actions and data can be expressed using the data
model that are understandable by the requester and allows it to
produce the API call and provide the required data. The only problem
with this mapping is that if the API call structure is different, the
logic required to call the target API might be complicated for
certain device applications.
With SDF notation, it is possible to explain the data model but not
the mapping for a specific API call. That would require, in some
cases, mapping of values and, depending on the API definition,
reshuffling of the parameters or even the URI utilized.
To tackle those challenges, we introduced a new SDF quality that can
express URL template patterns from [RFC6570]. The quality
*"template-href"*, includes the URL or the URL pattern that matches
the command known by the requester device application. As explained
in [RFC6570], the pattern may have variable terms, which are also
given an SDF definition and relationship so the requested device can
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understand how to map its own data model to what the target API
requires. Also, we introduce a value mapper *"template-value"* that
enables mapping of values to parameters in the target API. The
*sdfRelation* [I-D.ietf-asdf-sdf] is used as a vehicle to support the
mapping between APIs.
The namespace *"cmd"* is also utilized to provide this API mapping
values. In this example, we map a command_1 with several inputs to a
command_2 that utilizes the inputs in a different way. The schema
maps semantically the inputs and instructs the system how to make the
API call based on the previously known API.
{
"info":{
"title": "API mapping of two systems"
},
"namespace": {
"targetSem": "https://example.org/targetSemantics/#",
"targetDev": "https://example.org/targetDevice",
"requestDev": "https://example.com/requesterDevice",
"requestSem": "https://example.com/destinationSemantics/#"
},
"defaultNamespace": "requestSem",
"sdfData": {
"input_2_required": {
"type": "number",
"sdfChoice": {
"requesterSemantic_1": {
"const": 1
},
"requesterSemantic_2": {
"const": 2
}
},
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"targetDev:#/sdfObject/target_object/sdfAction/Name_of_the_command_1/sdfInputData/input2",
"requestDev:#/sdfObject/request_object/sdfAction/requester_command/sdfInputData/semanticRequesterInput"
]
}
}
}
},
"map": {
"#/sdfObject/request_object/sdfAction/requester_command": {
"cmd:template-href": "https://example.org/targetDevice/control/Name_of_the_command_1?input1={input_2_required}&input2={input_1}",
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"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"targetDev:#/sdfObject/target_object/sdfAction/Name_of_the_command_1",
"requestSem:requester_command"
]
}
}
},
"cmd :template-values": {
"input2": "#/sdfData/input_1_required",
"input1": "#/sdfObject/target_object/sdfAction/name_of_command1/sdfInputData/input_1"
},
"#/sdfObject/request_object/sdfAction/requester_command_2": {
"cmd:template-href": "https://example.org/targetDevice/control/Name_of_the_command_2?secondInput={requesterSecondInput}",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": "targetDev:#/sdfObject/target_object/sdfAction/Name_of_the_command_2"
}
}
},
"cmd:template-values": {
"secondInput": "#/sdfObject/request_object/sdfAction/requester_command_2/sdfInputData/requesterSecondInput"
}
}
}
4. Methods on the API calls
Sometimes, only calling an API is not enough. For example, in some
cases, the API call requires additional actions such as submitting a
payload. To handle this dimension on the API calls, the *method*
command has been introduced. This command enables the requested
device to understand how to handle the API call, since in the
previous example, the API URL has all the information required in the
call itself. However, in some cases, the action necessary with the
API may need to be specified in a manner that the requested device
can understand. The keyword *method* is meant to describe how to
handle the API URL and what to expect of it. In some other examples,
the *method* could result in an OBSERVE or another type of new action
not yet specified, for example, how to address an XR-type
application.
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An example could be the use of an LWM2M camera [lwm2m-cameraObject].
To use this model, a payload has to be submitted in the POST method.
The following example describes such a translation from one camera
API to the LWM2M model.
{
"info": {
"title": "LwM2M Camera Device to Requester dev. Application API mapping"
},
"namespace": {
"sdm": "https://sdm.wide.ad.jp/sdmo/#/",
"rdf": "http://www.w3.org/1999/02/22-rdf-syntax-ns",
"oma": "https://onedm.org/ecosystem/oma",
"dev": "http://traffic-light202125.traffic-center.fi/10340/0/",
"app": "http://owner.mycar.fi/"
},
"defaultNamespace": "dev",
"map": {
"#/sdfObject/video/sdfAction/playStream": {
"cmd:template-href": "http://traffic-light202125.traffic-center.fi/10340/0/101",
"cmd:method":"POST",
"description": "Starts the recording of the camera",
"sdfInputData": {
"type": "number",
"const":1
},
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"dev:#/sdfObject/Camera/sdfAction/Local_Recording_Control",
"oma:#/sdfObject/10340/101",
"sdm:playStream" ]
}
}
},
"#/sdfObject/video/sdfAction/StopStream": {
"cmd:template-href": "http://traffic-light202125.traffic-center.fi/10340/0/101",
"cmd:method":"POST",
"description": "Stops the recording of the camera",
"sdfInputData": {
"type": "number",
"const":0
},
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
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"dev:#/sdfObject/Camera/sdfAction/Local_Recording_Control",
"oma:#/sdfObject/10340/101",
"sdm:stopStream"
]
}
}
},
"#/sdfObject/Camera/sdfProperty/Input-video-stream":{
"cmd:template-href": "http://traffic-light202125.traffic-center.fi/10340/0/9",
"sdfRelation": {
"FeedType": {
"relType": "rdf:type",
"target": [
"dev:#/sdfObject/Camera/sdfProperty/Recording_Location",
"sdm:VideoMedia"
]
}
}
}
}
}
5. Matching API to application logic
Each application has a logic that requires either information from
the API call or the execution of a service. With this translation
tool, the application logic may need to consider the different types
of APIs that may be present. For example, if the API requires a
payload or the info is directly appended to the call. Also, on the
way the API produces the output, and how to handle it.
6. IANA Considerations
This document has the following actions for IANA.
Note to RFC Editor: Please replace all occurrences of "{XXXX}" with
the RFC number of this specification and delete this paragraph.
6.1. Media Type
IANA is requested to add the following Media-Type to the "Media Types
registry [IANA.media-types]. -->
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+==================+===============================+=============+
| Name | Template | Reference |
+==================+===============================+=============+
| sdf-mapping+json | application/ sdf-mapping+json | RFC XXXX, |
| | | section 5.1 |
+------------------+-------------------------------+-------------+
Table 1: A media type for SDF mapping files
7. Security Considerations
Some wider issues are discussed in [RFC8576].
8. Acknowledgements
Thanks to Ari Keränen for the support in realizing this idea.
9. References
9.1. Normative References
[I-D.ietf-asdf-sdf]
Koster, M., Bormann, C., and A. Keränen, "Semantic
Definition Format (SDF) for Data and Interactions of
Things", Work in Progress, Internet-Draft, draft-ietf-
asdf-sdf-24, 27 July 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-asdf-
sdf-24>.
[IANA.media-types]
IANA, "Media Types",
<https://www.iana.org/assignments/media-types>.
[RFC7396] Hoffman, P. and J. Snell, "JSON Merge Patch", RFC 7396,
DOI 10.17487/RFC7396, October 2014,
<https://www.rfc-editor.org/rfc/rfc7396>.
9.2. Informative References
[bormann-mapping]
Bormann, C. and J. Romann, "Semantic Definition Format
(SDF): Mapping files", n.d.,
<https://datatracker.ietf.org/doc/draft-bormann-asdf-sdf-
mapping/>.
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[lwm2m-cameraObject]
"Camera - OMAobjectId: 10340 V1.0", n.d.,
<https://raw.githubusercontent.com/OpenMobileAlliance/
lwm2m-registry/prod/10340.xml>.
[RFC6570] Gregorio, J., Fielding, R., Hadley, M., Nottingham, M.,
and D. Orchard, "URI Template", RFC 6570,
DOI 10.17487/RFC6570, March 2012,
<https://www.rfc-editor.org/rfc/rfc6570>.
[RFC8615] Nottingham, M., "Well-Known Uniform Resource Identifiers
(URIs)", RFC 8615, DOI 10.17487/RFC8615, May 2019,
<https://www.rfc-editor.org/rfc/rfc8615>.
Author's Address
Edgar Ramos
Ericsson
Hirsalantie 11
FI- 02420 Jorvas, Kirkkonummi
Finland
Email: edgar.ramos@ericsson.com
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