Network Working Group C. Bormann Internet-Draft Universität Bremen TZI Intended status: Standards Track 29 August 2022 Expires: 2 March 2023 Using CDDL for CSVs draft-bormann-cbor-cddl-csv-01 Abstract 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. 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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Code Components Bormann Expires 2 March 2023 [Page 1] Internet-Draft CDDL for CSVs August 2022 extracted from this document must include Revised BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Revised BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2 2. CSV generic data model . . . . . . . . . . . . . . . . . . . 2 3. Examples . . . . . . . . . . . . . . . . . . . . . . . . . . 3 4. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4 5. Security considerations . . . . . . . . . . . . . . . . . . . 5 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5 6.1. Normative References . . . . . . . . . . . . . . . . . . 5 6.2. Informative References . . . . . . . . . . . . . . . . . 5 Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . . 6 Author's Address . . . . . . . . . . . . . . . . . . . . . . . . 6 1. Introduction The Concise Data Definition Language (CDDL), standardized in [RFC8610], is defined to provide data models for data shaped like JSON or CBOR. Another representation format that is quote popular is the CSV file as defined by [RFC4180]. The present document shows how to use CDDL to provide a data model for CSV files. 1.1. 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. This specification uses terminology from [RFC8610]. 2. CSV generic data model The CSV format is defined in [RFC4180]. The generic data model for the data in a CSV file can be described in CDDL as: Bormann Expires 2 March 2023 [Page 2] Internet-Draft CDDL for CSVs August 2022 csv = [?header, *record] header = [+header-field] record = [+field] header-field = text field = text Note that the elements of this data model describe the interpretation of the data after processing and removal of lexical structure such as newlines, commas, escape characters, and quotation marks. For the purposes of a specific application, the data model level structure of each field may be described in a more elaborate way, e.g., as a number. CDDL currently does not have a way to express the transformation from the text string in the CSV field to the number that this text string represents at the application data model level; the usage of anything but "text" for a field therefore MUST be accompanied by an instruction how to perform the translation. As a preferred choice, the JSON representation of the data model item, if it exists, MAY be chosen by that instruction. Since the CSV media type text/csv defaults to using the US-ASCII character set (i.e., [STD80]; see Section 3 of [RFC4180]), many uses of CSV will need to specify the media type parameter charset. (Note that CDDL can describe text information that is in UTF-8 form, which includes US-ASCII as that is a subset of UTF-8. If a different form that is not a subset of UTF-8 is really still needed, some rules for conversion will need to be defined by the application.) The media type parameter header MAY be used to indicate the presence or absence of a header line; if it is not given, the grammar MUST NOT be ambiguous about the presence of a header (i.e., it MUST be either mandatory or absent). Note that the ABNF [STD68] in [RFC4180] does not quite handle the case that charset is not us-ascii. For the purposes of the present specification, the ABNF is understood to allow all characters from the charset except %x22 and %x2C in TEXTDATA. For the purposes of the present specification, the ABNF rule CRLF is read as: CRLF = [CR] LF as is hinted in Section 3 of [RFC4180]. 3. Examples A simplified CSV form definition of a SID file [I-D.ietf-core-sid] might look like this: Bormann Expires 2 March 2023 [Page 3] Internet-Draft CDDL for CSVs August 2022 ; header = absent SID-File = [meta-record, *dependency-record, *range-record, *item-record] meta-record = ["meta", module-name: text, module-revision: empty / text, sid-file-revision: empty / text, description: empty / text] dependency-record = ["dep", module-name: text, module-revision: text] range-record = ["range", entry-point: uint, size: uint] item-record = ["item", namespace: "module" / "identity" / "feature" / "data", identifier: yang-identifier / schema-node-path ; the above probably should say which namespace ; goes with which identifier sid: uint] yang-identifier = text .abnf ("yang-identifier" .det id-abnf) schema-node-path = text .abnf ("schema-node-path" .det id-abnf) id-abnf = ' schema-node-path = QID *( "/" OQID) yang-identifier = ID QID = ID ":" ID OQID = ID [":" ID] ID = I *C I = "_" / %x41-5a / %x61-7a C = I / %x30-39 / "-" / "." ' empty = "" TODO: show the example in Appendix A of [I-D.ietf-core-sid] 4. IANA Considerations This document makes no requests of IANA. Bormann Expires 2 March 2023 [Page 4] Internet-Draft CDDL for CSVs August 2022 5. Security considerations The security considerations of [RFC8610] and [RFC4180] apply. 6. References 6.1. 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, . [RFC4180] Shafranovich, Y., "Common Format and MIME Type for Comma- Separated Values (CSV) Files", RFC 4180, DOI 10.17487/RFC4180, October 2005, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8610] Birkholz, H., Vigano, C., and C. Bormann, "Concise Data Definition Language (CDDL): A Notational Convention to Express Concise Binary Object Representation (CBOR) and JSON Data Structures", RFC 8610, DOI 10.17487/RFC8610, June 2019, . [STD68] Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax Specifications: ABNF", STD 68, RFC 5234, DOI 10.17487/RFC5234, January 2008, . 6.2. Informative References [I-D.ietf-core-sid] Veillette, M., Pelov, A., Petrov, I., Bormann, C., and M. Richardson, "YANG Schema Item iDentifier (YANG SID)", Work in Progress, Internet-Draft, draft-ietf-core-sid-19, 26 July 2022, . [STD80] Cerf, V., "ASCII format for network interchange", STD 80, RFC 20, DOI 10.17487/RFC0020, October 1969, . Bormann Expires 2 March 2023 [Page 5] Internet-Draft CDDL for CSVs August 2022 Acknowledgements Rob Wilton, unknowingly, made me write this specification. I hope it will be useful. Author's Address Carsten Bormann Universität Bremen TZI Postfach 330440 D-28359 Bremen Germany Phone: +49-421-218-63921 Email: cabo@tzi.org Bormann Expires 2 March 2023 [Page 6]