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CBOR Working group Internet-Draft The Concise Data Definition Language (CDDL) today is defined by RFC 8610 and RFC 9165. The latter (as well as some more application specific specifications such as RFC 9090) have used the extension point provided in RFC 8610, the control operator. As CDDL is used in larger projects, feature requirements become known that cannot be easily mapped into this single extension point. Hence, there is a need for evolution of the base CDDL specification itself. The present document provides a roadmap towards a "CDDL 2.0". It is based on draft-bormann-cbor-cddl-freezer, but is more selective in what potential features it takes up and more detailed in their discussion. It is intended to serve as a basis for prototypical implementations of CDDL 2.0. What specific documents spawn from the present one or whether this document is evolved into a single CDDL 2.0 specification. About This Document Status information for this document may be found at . Discussion of this document takes place on the cbor Working Group mailing list (), which is archived at . Subscribe at . Source for this draft and an issue tracker can be found at .

Introduction (Please see abstract.) Note that the existing extension point can be exercised for new features in parallel to the work described here. One such draft, , is planned to form the first set of specifications going forward from the CDDL-2 project together with . The rest of this introduction gives a rough overview over what could be the development plan for CDDL 1.1, 2.0, 2.5.

CDDL 1.1 + 2 plan (standards track)

• Done before IETF 117: CDDL 1.1: , Grammar fixes: Empty files (enabling CDDL 2), non-literal tags, errata fixes (implemented)
• Done before IETF 117: Parallel to CDDL 1.1: More control operators : Additional control operators, another iteration like RFC 9165 (implemented)
• Done before IETF 118: CDDL 2.0: (import/include implemented; potentially further directives to be added)
• Done 2024: CDDL 2.5: of the present document ("annotations", plus some functionality enabled by that). The requirements are clear, the specific form this takes needs to be worked out. Enables, e.g., (co-occurrence).

Other documents Not on the main line of development, but important ancillary work:

• (Informational, Mid-2023): : CDDL-in-JSON format(s) for interchange of CDDL model information between tools.
• (Informational, with ): (builds standard collection of referenceable models).
• (BCP?): (BCP for handling assigned numbers during draft stage)

More explorative at this point:

• (Standards-Track?) The remaining of this document: application-oriented literals in CDDL; develop with .
• (Informational or Standards-Track?): (using CDDL to model CSV documents).

Mending syntax deficits The previous content of this section formed the basis for , except for .

Tag-oriented Literals Incomplete, see .

Processing model: Beyond Validation

Proposal Status:

experiments with implementations ongoing

Compatibility:

backwards compatible

The basic (implicit) processing model for CDDL 1.0 applies a CDDL data model to a data item and returns a Boolean that indicates whether the data item matches that model ("validation"). extends this model with named "features". A validation can indicate which features were used. Validation could also be parameterized with information about what features are allowed to be used, enabling variants (see and for examples). The cddl tool () also supports experimental forms of "annotating" a validated data item with information about which rules were used to support validation, currently entirely based on the information that is in a standard CDDL 1.0 data model. This leads to a more general concept of "annotation", where the data model specification supports "annotating" the validated instance by optionally supplying information in the model. (The annotated result is a special case of a "post-schema validation instance" , here one where the data item itself is only augmented, not changed, by the process.) Annotations could in turn provide input to further validation steps, as is often done with Schematron validation in Relax-NG; with an appropriate evaluation language this can be used for checking co-occurrence constraints (). Finally, annotations are a first step to transformation, i.e., describing how a validated data item should be interpreted as a transformed data item by performing certain computations. This generally requires even more support from an evaluation language, simple transformations such as adding in default values may not need much support though. At this time, existing experimental implementations do not lead to a clear choice for what processing model enhancements should be in CDDL 2.0. This document proposes to continue the experimentation and document good approaches.

Module superstructure The previous content of this section formed the basis for . Additional work might be started on the ideas outlined in the subsections of this section.

Cross-universe references See .

ABNF is a lot like CDDL Many of the constructs defined here for CDDL also could be used with ABNF specifications. ABNF would definitely benefit from a standard way to import snippets from existing RFCs. Since CDDL contains ABNF support (), it would be natural to make some of the functionality discussed in this section available for ABNF as well.

IANA Considerations (Insert new registry for application specific literals here, if adopted.)

Security considerations The security considerations of apply.

References Normative References This document proposes a notational convention to express Concise Binary Object Representation (CBOR) data structures (RFC 7049). Its main goal is to provide an easy and unambiguous way to express structures for protocol messages and data formats that use CBOR or JSON. The Concise Data Definition Language (CDDL), standardized in RFC 8610, provides "control operators" as its main language extension point. The present document defines a number of control operators that were not yet ready at the time RFC 8610 was completed: , , and for the construction of constants; / for including ABNF (RFC 5234 and RFC 7405) in CDDL specifications; and for indicating the use of a non-basic feature in an instance. Informative References Universität Bremen TZI In defining the Concise Data Definition Language (CDDL), some features have turned up that would be nice to have. In the interest of completing this specification in a timely manner, the present document was started to collect nice-to-have features that did not make it into the first RFC for CDDL, RFC 8610, or the specifications exercising its extension points, such as RFC 9165. Significant parts of this draft have now moved over to the CDDL 2.0 project, described in draft-bormann-cbor-cddl-2-draft. The remaining items in this draft are not directly related to the CDDL 2.0 effort. Universität Bremen TZI The Concise Binary Object Representation, CBOR (RFC 8949), defines a "diagnostic notation" in order to be able to converse about CBOR data items without having to resort to binary data. This document specifies how to add application-oriented extensions to the diagnostic notation. It then defines two such extensions for the use of CBOR diagnostic notation with CoRAL and Constrained Resource Identifiers (draft-ietf-core-coral, draft-ietf-core-href). Universität Bremen TZI At the time of writing, the Concise Data Definition Language (CDDL) is defined by RFC 8610 and RFC 9165. The latter has used the extension point provided in RFC 8610, the _control operator_. As CDDL is being used in larger projects, the need for corrections and additional features has become known that cannot be easily mapped into this single extension point. Hence, there is a need for evolution of the base CDDL specification itself. The present document updates errata and makes other small fixes for the ABNF grammar defined for CDDL in RFC 8610. // Previous versions of the changes in this document were part of // draft-bormann-cbor-cddl-2-draft and previously draft-bormann-cbor- // cddl-freezer. This submission extracts out those grammar changes // that are ready for WG adoption and publication. Universität Bremen TZI The Concise Data Definition Language (CDDL), standardized in RFC 8610, provides "control operators" as its main language extension point. RFCs have added to this extension point both in an application-specific and a more general way. The present document defines a number of additional generally application control operators for text conversion (Bytes, Integers, JSON), operations on text, and deterministic encoding. // Revision -01 of this draft reflects comments from initial // discussion of the specification in the CBOR working group. It is // intended to be ready for working group adoption. Universität Bremen TZI At the time of writing, the Concise Data Definition Language (CDDL) is defined by RFC 8610 and RFC 9165. The latter has used the extension point provided in RFC 8610, the _control operator_. As CDDL is being used in larger projects, the need for corrections and additional features has become known that cannot be easily mapped into this single extension point. Hence, there is a need for evolution of the base CDDL specification itself. The present document defines a backward- and forward-compatible way to add a module structure to CDDL. // Previous versions of the changes in this document were part of // draft-bormann-cbor-cddl-2-draft and previously draft-bormann-cbor- // cddl-freezer. This submission extracts out the functionality that // is ready for WG adoption and further WG work. Universität Bremen TZI A number of CBOR- and JSON-based protocols have been defined before CDDL was standardized or widely used. This short draft records some CDDL definitions for such protocols, which could become part of a library of CDDL definitions available for use in CDDL2 processors. It focuses on CDDL in (almost) published IETF RFCs. Universität Bremen TZI CBOR-based protocols often make use of numbers allocated in a registry. While developing the protocols, those numbers may not yet be available. This impedes the generation of data models and examples that actually can be used by tools. This short draft proposes a common way to handle these situations, without any changes to existing tools. Such changes are very well possible in the future, at which time this draft will be updated. Universität Bremen TZI The Concise Data Definition Language (CDDL), standardized in RFC 8610, is defined to provide data models for data shaped like JSON or CBOR. Another representation format that is quote popular is the CSV (Comma-Separated Values) file as defined by RFC 4180. The present document shows a way how to use CDDL to provide a data model for CSV files. n.d.

Fridge This appendix contains sections that may not make it to a 2.0, but might be part of a followup.

Tag-oriented Literals

Proposal Status:

rough idea, porting from EDN

Compatibility:

backward (not forward)

Some CBOR tags often would be most natural to use in a CDDL spec with a literal syntax that is tailored to their semantics instead of their serialization in CBOR. There is currently no way to add such syntaxes, no defined extension point either. The proposal "Application-Oriented Literals in CBOR Extended Diagnostic Notation" defines application-oriented literals, e.g., of the form

• dt'2019-07-21T19:53Z'

for datetime items. With additional considerations for unambiguous syntax, a similar literal form could be included in CDDL. This proposal opens a name space for the prefix that indicates an application specific literal. A registry could be provided to make this name space a genuine extension point. (This is currently the production bsqual in .) The syntax provided in does not enable the use of CDDL types — it has the same flaw that is being fixed for tag numbers in .

Cross-universe references Often, a CDDL specification needs to import from specifications in a different language or platform.

IANA references In many cases, CDDL specifications make use of values that are specified in IANA registries. The .iana control operator can be used to reference such a set of values. The reference needs to be able to point to a draft, the registry of which has not been established yet, as well as to an established IANA registry. An example of such a usage might be: Unfortunately, the vocabulary employed in IANA registries has not been designed for machine references. In this case, the potential values would come from applying the XPath expression to https://www.iana.org/assignments/cose/cose.xml, plus some filtering on the records returned that only leaves actual allocations. Additional functionality may be needed for filtering with respect to other columns of the registry record, e.g., <capabilities> in the case of this example.

Acknowledgements TBD