Using CDDL for CSVs

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Table of Contents

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.¶

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:¶

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:¶

; 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.¶

5. Security considerations

The security considerations of [RFC8610] and [RFC4180] apply.¶

Acknowledgements

Rob Wilton, unknowingly, made me write this specification. I hope it will be useful.¶

Author's Address