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Copyright Notice

Copyright © The Internet Society (2005).

Abstract

This document documents the format used for Comma-Separated Values (CSV) files and registers the associated MIME type "text/csv".

Table of Contents

1.  Introduction
2.  Definition of the CSV format
3.  MIME Type Registration of text/csv
4.  IANA Considerations
5.  Security Considerations
6.  Acknowledgments
7.  References
    7.1  Normative References
    7.2  Informative References
§  Author's Address
A.  Status of This Document [To Be Removed Upon Publication]
    A.1  Discussion Venue
    A.2  Document Repository
    A.3  Document History
§  Intellectual Property and Copyright Statements

1. Introduction

The comma separated values format (CSV) has been used for exchanging and converting data between various spreadsheet programs for quite some time. Surprisingly, while this format is very common it has never been formally documented. Additionally, while the IANA MIME registration tree includes a registration for "text/tab-separated-values" type, no MIME types have ever been registered with IANA for CSV. At the same time, various programs and operating systems have begun to use different MIME types for this format, many of which vary from system to system. This document seeks to document the format of comma separated values (CSV) files and to formally register the "text/csv" MIME type for CSV in accordance with RFC 2048 (Freed, N., Klensin, J., and J. Postel, “Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures,” November 1996.)[1].

2. Definition of the CSV format

While there are various specifications and implementations for the CSV format (for ex. [4] (Repici, J., “HOW-TO: The Comma Separated Value (CSV) File Format,” 2004.), [5] (Edoceo, Inc., “CSV Standard File Format,” 2004.), [6] (Rodger, R. and O. Shanaghy, “Documentation for Ricebridge CSV Manager,” February 2005.) and [7] (Raymond, E., “The Art of Unix Programming, Chapter 5,” September 2003.)), no formal specification exists which causes a wide variety of interpretations for CSV files. This section seeks to document the format that seems to be followed by most implementations:

1. Each record is located on a separate line delimited by a line break (CRLF). For example:
   
   aaa,bbb,ccc CRLF
   zzz,yyy,xxx CRLF
2. The last record in the file may or may not have an ending line break. For example:
   
   aaa,bbb,ccc CRLF
   zzz,yyy,xxx
3. There maybe an optional header line appearing as the first line of the file with the same format as normal record lines. This header will contain names corresponding to the fields in the file and should contain the same number of fields as the records in the rest of the file (the presence or absence of the header line should be indicated via the optional "header" parameter of this MIME type). For example:
   
   field_name,field_name,field_name CRLF
   aaa,bbb,ccc CRLF
   zzz,yyy,xxx CRLF
4. Within the header and each record there may be one or more fields, separated by commas. Each line should contain the same number of fields throughout the file. The last field in the record may not be followed by a comma. For example:
   
   aaa,bbb,ccc
5. Each field may or may not be enclosed in double quotes (however some programs such as Microsoft Excel do not use double quotes at all). If fields are not enclosed with double quotes, then double quotes may not appear inside the fields. For example:
   
   "aaa","bbb","ccc" CRLF
   zzz,yyy,xxx
6. Field containing line breaks (CRLF), double quotes and commas should be enclosed in double-quotes. For example:
   
   "aaa","b CRLF
   bb","ccc" CRLF
   zzz,yyy,xxx
7. If double-quotes are used to enclosed fields, then a double-quote appearing inside a field must be escaped by preceding it with another double quote. For example:
   
   "aaa","b""bb","ccc"

The ABNF grammar (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.)[2] appears as follows:

file = [header CRLF] record *(CRLF record) [CRLF]

header = name *(COMMA name)

record = field *(COMMA field)

name = field

field = (escaped / non-escaped)

escaped = DQUOTE *(TEXTDATA / COMMA / CR / LF / 2DQUOTE) DQUOTE

non-escaped = *TEXTDATA

COMMA = %x2C

CR = %x0D ;as per section 6.1 of RFC 2234 (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.)[2]

DQUOTE = %x22 ;as per section 6.1 of RFC 2234 (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.)[2]

LF = %x0A ;as per section 6.1 of RFC 2234 (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.)[2]

CRLF = CR LF ;as per section 6.1 of RFC 2234 (Crocker, D., Ed. and P. Overell, “Augmented BNF for Syntax Specifications: ABNF,” November 1997.)[2]

TEXTDATA = %x20-21 / %x23-2B / %x2D-7E

3. MIME Type Registration of text/csv

This section provides the media-type registration application (as per RFC 2048 (Freed, N., Klensin, J., and J. Postel, “Multipurpose Internet Mail Extensions (MIME) Part Four: Registration Procedures,” November 1996.)[1], which will be submitted to IANA after IESG approval of this document.

To: ietf-types@iana.org

Subject: Registration of MIME media type text/csv

MIME media type name: text

MIME subtype name: csv

Required parameters: none

Optional parameters: charset, header

Common usage of CSV is US-ASCII, but other character sets as defined by IANA for the "text" tree may be used in conjuction with the "charset" parameter.

The "header" parameter indicates the presence or absence of the header line. Valid values are "present" or "absent". Implementators choosing not to use this parameter must make their own decisions as to whether the header line is present or absent.

Encoding considerations:

As per section 4.1.1. of RFC 2046 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types,” November 1996.)[3], this media type uses CRLF to denote line breaks. However, implementors should be aware that some implementations may use other values.

Security considerations:

CSV files contain passive text data which should not pose any risks. However, it is possible in theory that malicious binary data maybe included in order to exploit potential buffer overruns in the program processing CSV data. Additionally, private data maybe shared via this format (which of course applies to any text data).

Interoperability considerations:

Due to lack of a single specification there are considerable differences among different implementations. Implementors should "be conservative in what you do, be liberal in what you accept from others" (RFC 793 (Postel, J., “Transmission Control Protocol,” September 1981.)[8]) when processing CSV files. An attempt at a common definition can be found in Section 2 (Definition of the CSV format).

Implementations deciding not to use the optional "header" parameter must make their own decision as to whether the header is absent or present.

Published specification:

While numerous private specifications exist for various programs and systems, there is no single "master" specification for this format. An attempt at a common definition can be found in Section 2 (Definition of the CSV format).

Applications which use this media type:

Spreadsheet programs and various data conversion utilities

Additional information:

Magic number(s): none

File extension(s): CSV

Macintosh File Type Code(s): TEXT

Person & email address to contact for further information:

Yakov Shafranovich <ietf@shaftek.org>

Intended usage: COMMON

Author/Change controller: IESG

4. IANA Considerations

After IESG approval, IANA is expected to register the MIME type "text/csv" using the application provided in Section 3 (MIME Type Registration of text/csv) of this document.

5. Security Considerations

See discussion above

6. Acknowledgments

The author would like to thank Dave Crocker, Martin Duerst, Joel M. Halpern, Clyde Ingram, Graham Klyne, Bruce Lilly, Chris Lilley and members of the IESG for their helpful suggestions. A special word of thanks to Dave for helping with the ABNF grammar.

The author would also like to thank Henrik Lefkowetz, Marshall Rose and the folks at xml.resource.org for providing many of the tools used for preparing RFCs and Internet drafts.

7. References

7.1 Normative References

7.2 Informative References

Author's Address

Appendix A. Status of This Document [To Be Removed Upon Publication]

A.1 Discussion Venue

Discussion about this document should be directed to the IETF-TYPES mailing list http://www.alvestrand.no/mailman/listinfo/ietf-types/ which is also reachable via ietf-types@iana.org. Of course, comments directly to the author are always welcome.

A.2 Document Repository

Copies of this and earlier versions including multiple formats can be found at http://www.shaftek.org/publications/drafts/mime-csv/.

A.3 Document History

Changes from draft-shafranovich-mime-csv-04 to draft-shafranovich-mime-csv-05:

• Fixes in ABNF grammar: comma excluded from TEXTDATA and added to escaped text, 2*DQUOTE changed to 2DQUOTE.

Changes from draft-shafranovich-mime-csv-03 to draft-shafranovich-mime-csv-04:

• Fixed ABNF grammar in response to IESG comments: VCHAR changed to TEXTDATA, DQUOTE excluded from TEXTDATA, spaces are included in TEXTDATA, CRLF taken out since CR and LF are already included.
• Added clarification that double quotes may not be included inside non-quoted fields.
• Added clarification that the same number of fields should appear in every line.
• Added the optional "header" parameter to indicate the presence or absence of a header line.

Changes from draft-shafranovich-mime-csv-02 to draft-shafranovich-mime-csv-03:

• Changed text to prohibit the last field ending with a comma matching the ABNF grammar
• The double quote escaping is now set to two double quotes instead of three
• Moved some of the references between informative and normative sections

Changes from draft-shafranovich-mime-csv-01 to draft-shafranovich-mime-csv-02:

• Minor errors in ABNF grammar corrected in response to AD comments
• Minor spelling mistakes corrected

Changes from draft-shafranovich-mime-csv-00 to draft-shafranovich-mime-csv-01:

• Type "text/comma-separated-values" has been removed
• The "encoding consideration" paragraph of Section 3 (MIME Type Registration of text/csv) has been changed to allow CRLF only as per section 4.1.1. of RFC 2046 (Freed, N. and N. Borenstein, “Multipurpose Internet Mail Extensions (MIME) Part Two: Media Types,” November 1996.)[3]. This has been reflected in the ABNF grammar in Section 2 (Definition of the CSV format).
• ABNF grammar in Section 2 (Definition of the CSV format) has been cleaned up.
• Acknowledgements and status sections were added.
• CSV format definition was moved to the normative section of the document

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Copyright Statement

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