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Internet-Draft 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.

Introduction The Concise Data Definition Language (CDDL), standardized in , 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 . The present document shows how to use CDDL to provide a data model for CSV files.

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 () () when, and only when, they appear in all capitals, as shown here. This specification uses terminology from .

CSV generic data model The CSV format is defined in . The generic data model for the data in a CSV file can be described in CDDL as: 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. A recently published CDDL extension, , provides some CDDL control operators that could be used to express the transformation between the text string in the CSV field and the number that this text string represents at the application data model level; this could be explored in future revisions of this specification. For now, 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., ; see ), 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 in 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: as is hinted in .

Examples A simplified CSV form definition of a SID file might look like this: This CDDL data model assumes that the text strings representing the numbers entry-point, size, and sid are converted to uint. (Note that, due to the way YANG-JSON defines the representation of uint64 data items, these actually are text strings in JSON, which in CSV is indistinguishable from numbers. However, the CDDL model for the CSV files will be more useful if it takes into account typical CSV applications that automatically convert integer-like text strings into numbers.) The result of representing in CSV the sid file ietf-system.sid (as defined in ) is shown in .

IANA Considerations This document makes no requests of IANA.

Security considerations The security considerations of and 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. This RFC documents the format used for Comma-Separated Values (CSV) files and registers the associated MIME type "text/csv". This memo provides information for the Internet community. Internet technical specifications often need to define a formal syntax. Over the years, a modified version of Backus-Naur Form (BNF), called Augmented BNF (ABNF), has been popular among many Internet specifications. The current specification documents ABNF. It balances compactness and simplicity with reasonable representational power. The differences between standard BNF and ABNF involve naming rules, repetition, alternatives, order-independence, and value ranges. This specification also supplies additional rule definitions and encoding for a core lexical analyzer of the type common to several Internet specifications. [STANDARDS-TRACK] In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. Informative References YANG Schema Item iDentifiers (YANG SIDs) are globally unique 63-bit unsigned integers used to identify YANG items. SIDs provide a more compact method for identifying those YANG items that can be used efficiently, notably in constrained environments (RFC 7228). This document defines the semantics, registration processes, and assignment processes for YANG SIDs for IETF-managed YANG modules. To enable the implementation of these processes, this document also defines a file format used to persist and publish assigned YANG SIDs. 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 in both an application-specific and a more general way. The present document defines a number of additional generally applicable control operators for text conversion (bytes, integers, printf-style formatting, and JSON) and for an operation on text. This document defines encoding rules for representing configuration data, state data, parameters of Remote Procedure Call (RPC) operations or actions, and notifications defined using YANG as JavaScript Object Notation (JSON) text. This document defines two strategies for handling long lines in width-bounded text content. One strategy, called the "single backslash" strategy, is based on the historical use of a single backslash ('\') character to indicate where line-folding has occurred, with the continuation occurring with the first character that is not a space character (' ') on the next line. The second strategy, called the "double backslash" strategy, extends the first strategy by adding a second backslash character to identify where the continuation begins and is thereby able to handle cases not supported by the first strategy. Both strategies use a self-describing header enabling automated reconstitution of the original content.

Example: ietf-system.sid represented in CSV This appendix shows the CSV file that is automatically generated from . (Note that plaintext-based RFCs are limited to 72 columns; therefore five long lines in the CSV file have been folded as defined in .)

Acknowledgements Rob Wilton, unknowingly, made us write this specification. We hope it will be useful. Laurent Toutain inspired the SID CDDL format with an example.