URI Fragment Identifiers for the text/csv Media Type

Independent Submission                                     M. Hausenblas
Request for Comments: 7111                             MapR Technologies
Updates: 4180                                                   E. Wilde
Category: Informational                                      UC Berkeley
ISSN: 2070-1721                                              J. Tennison
                                                     Open Data Institute
                                                            January 2014


          URI Fragment Identifiers for the text/csv Media Type

Abstract

   This memo defines URI fragment identifiers for text/csv MIME
   entities.  These fragment identifiers make it possible to refer to
   parts of a text/csv MIME entity identified by row, column, or cell.
   Fragment identification can use single items or ranges.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor are not a candidate for any level of Internet
   Standard; see Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc7111.

IESG Note

   The change to the text/csv media type registration requires IESG
   approval, as the IESG is the change controller for that registration.
   The IESG has, after consultation with the IETF community, approved
   the change, which is specified in Section 5 of this document.

Copyright Notice

   Copyright (c) 2014 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  What is text/csv? . . . . . . . . . . . . . . . . . . . .   3
     1.2.  Why text/csv Fragment Identifiers?  . . . . . . . . . . .   3
       1.2.1.  Motivation  . . . . . . . . . . . . . . . . . . . . .   3
       1.2.2.  Use Cases . . . . . . . . . . . . . . . . . . . . . .   4
     1.3.  Incremental Deployment  . . . . . . . . . . . . . . . . .   4
     1.4.  Notation Used in this Memo  . . . . . . . . . . . . . . .   4
   2.  Fragment Identification Methods . . . . . . . . . . . . . . .   5
     2.1.  Row-Based Selection . . . . . . . . . . . . . . . . . . .   5
     2.2.  Column-Based Selection  . . . . . . . . . . . . . . . . .   6
     2.3.  Cell-Based Selection  . . . . . . . . . . . . . . . . . .   6
     2.4.  Multi-Selections  . . . . . . . . . . . . . . . . . . . .   7
   3.  Fragment Identification Syntax  . . . . . . . . . . . . . . .   7
   4.  Fragment Identifier Processing  . . . . . . . . . . . . . . .   8
     4.1.  Syntax Errors in Fragment Identifiers . . . . . . . . . .   8
     4.2.  Semantics of Fragment Identifiers . . . . . . . . . . . .   8
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   9
     5.1.  The text/csv media type . . . . . . . . . . . . . . . . .   9
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  11
   7.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .  11
     8.2.  Informative References  . . . . . . . . . . . . . . . . .  12

1.  Introduction

   This memo updates the text/csv media type defined in RFC 4180
   [RFC4180] by defining URI fragment identifiers for text/csv MIME
   entities.

   The change to the text/csv media type registration required IESG
   approval, as the IESG is the change controller for that registration.
   The IESG has, after consultation with the IETF community, approved
   the change, which is specified in Section 5 of this document.

   This section gives an introduction to the general concepts of
   text/csv MIME entities and URI fragment identifiers and discusses the
   need for fragment identifiers for text/csv and deployment issues.
   Section 2 discusses the principles and methods on which this memo is
   based.  Section 3 defines the syntax, and Section 4 discusses
   processing of text/csv fragment identifiers.

1.1.  What is text/csv?

   Internet Media Types (often referred to as "MIME types") as defined
   in RFC 2045 [RFC2045] and RFC 2046 [RFC2046] are used to identify
   different types and subtypes of media.  The text/csv media type is
   defined in RFC 4180 [RFC4180], using US-ASCII [ASCII] as the default
   character encoding (other character encodings can be used as well).
   Apart from a media type parameter for specifying the character
   encoding ("charset"), there is a second media type parameter
   ("header") that indicates whether there is a header row in the CSV
   document or not.

1.2.  Why text/csv Fragment Identifiers?

   URIs are the identification mechanism for resources on the Web.  The
   URI syntax specified in RFC 3986 [RFC3986] optionally includes a so-
   called "fragment identifier", separated by a number sign ("#").  The
   fragment identifier consists of additional reference information to
   be interpreted by the client after the retrieval action has been
   successfully completed.  The semantics of a fragment identifier is a
   property of the media type resulting from a retrieval action,
   regardless of the URI scheme used in the URI reference.  Therefore,
   the format and interpretation of fragment identifiers is dependent on
   the media type of the retrieval result.

1.2.1.  Motivation

   Similar to the motivation in RFC 5147 [RFC5147], which defines
   fragment identifiers for plain text files, referring to specific
   parts of a resource can be very useful because it enables users and
   applications to create more specific references.  Users can create
   references to a particular point of interest within a resource,
   rather than referring to the complete resource.  Even though it is
   suggested that fragment identification methods are specified in a
   media type's registration (see [RFC6838]), many media types do not
   have fragment identification methods associated with them.

   Fragment identifiers are only useful if supported by the client,
   because they are only interpreted by the client.  Therefore, a new
   fragment identification method will require some time to be adopted
   by clients, and older clients will not support it.  However, because
   the URI still works even if the fragment identifier is not supported
   (the resource is retrieved, but the fragment identifier is not
   interpreted), rapid adoption is not highly critical to ensure the
   success of a new fragment identification method.

1.2.2.  Use Cases

   Fragment identifiers for text/csv as defined in this memo make it
   possible to refer to specific parts of a text/csv MIME entity.  Use
   cases include, but are not limited to, selecting a part for visual
   rendering, stream processing, making assertions about a certain value
   (provenance, confidence, comments, etc.), or data integration.

1.3.  Incremental Deployment

   As long as text/csv fragment identifiers are not supported
   universally, it is important to consider the implications of
   incremental deployment.  Clients (for example, Web browsers) not
   supporting the text/csv fragment identifier described in this memo
   will work with URI references to text/csv MIME entities, but they
   will fail to understand the identification of the sub-resource
   specified by the fragment identifier, and thus will behave as if the
   complete resource was referenced.  This is a reasonable fallback
   behavior and, in general users, should take into account the
   possibility that a program interpreting a given URI will fail to
   interpret the fragment identifier part.  Since fragment identifier
   evaluation is local to the client (and happens after retrieving the
   MIME entity), there is no reliable way for a server to determine
   whether a requesting client is using a URI containing a fragment
   identifier.

1.4.  Notation Used in this Memo

   The capitalized key words "MUST", "MUST NOT", "REQUIRED", "SHALL",
   "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in RFC
   2119 [RFC2119].

2.  Fragment Identification Methods

   This memo specifies fragment identification using the following
   methods: "row" for row selections, "col" for columns selections, and
   "cell" for cell selections.

   Throughout the sections below, the following example table in CSV
   (having 7 rows, including one header row, and 3 columns) is used:

   date,temperature,place
   2011-01-01,1,Galway
   2011-01-02,-1,Galway
   2011-01-03,0,Galway
   2011-01-01,6,Berkeley
   2011-01-02,8,Berkeley
   2011-01-03,5,Berkeley

2.1.  Row-Based Selection

   To select a specific record, the "row" scheme followed by a single
   number is used (the first row is at position 1).

   http://example.com/data.csv#row=4

   The above CSV fragment identifies the fourth row:

   2011-01-03,0,Galway

   Fragments can also select ranges of rows:

   http://example.com/data.csv#row=5-7

   The above CSV fragment identifies three consecutive rows:

   2011-01-01,6,Berkeley
   2011-01-02,8,Berkeley
   2011-01-03,5,Berkeley

   The value "*" can be used to indicate the last row, so the previous
   URI is equivalent to:

   http://example.com/data.csv#row=5-*

2.2.  Column-Based Selection

   To select values from a certain column, the "col" scheme is used,
   followed by a position (the first column is at position 1):

   http://example.com/data.csv#col=2

   The above CSV fragment addresses the second column, identifying the
   column:

   temperature
   1
   -1
   0
   6
   8
   5

   The "col" scheme can also be used to identify ranges of columns:

   http://example.com/data.csv#col=1-2

   The above CSV fragment addresses the first and second column:

   date,temperature
   2011-01-01,1
   2011-01-02,-1
   2011-01-03,0
   2011-01-01,6
   2011-01-02,8
   2011-01-03,5

   As for rows, the value "*" can be used to indicate the last column.

2.3.  Cell-Based Selection

   To select particular fields, the "cell" scheme is used, followed by a
   row number, a comma, and a column number.

   http://example.com/data.csv#cell=4,1

   The above CSV fragment addresses the field in the first column within
   the fourth row, yielding:

   2011-01-03
   It is also possible to select cell-based fragments that have more
   than just one cell, in which case the cell selection uses the same
   range syntax as for row and column range selections.  For these
   selections, the syntax uses the upper left-hand cell as the starting
   point of the selection, followed by a minus sign, and then the lower
   right-hand cell as the end point of the selection.

   http://example.com/data.csv#cell=4,1-6,2

   The above CSV fragment selects a region that starts at the fourth row
   and the first column and ends at the sixth row and the second column:

   2011-01-03,0
   2011-01-01,6
   2011-01-02,8

2.4.  Multi-Selections

   Row, column, and cell selections can make more than one selection, in
   which case the individual selections are separated by semicolons.  In
   these cases, the resulting fragment may be a disjoint fragment, such
   as the selection "#row=3;6" for the example CSV, which would select
   the third and the sixth row.  It is up to the user agent to decide
   how to handle disjoint fragments, but since they are allowed, user
   agents should be prepared to handle disjoint fragments.

3.  Fragment Identification Syntax

   The syntax for the text/csv fragment identifiers is as follows.

   The following syntax definition uses ABNF as defined in RFC 5234
   [RFC5234], including the rule DIGIT.

   NOTE:  In the descriptions that follow, specified text values MUST be
      used exactly as given, using exactly the indicated lowercase
      letters.  In this respect, the ABNF usage differs from [RFC5234].

   csv-fragment =  rowsel / colsel / cellsel
   rowsel       =  "row=" singlespec 0*( ";" singlespec)
   colsel       =  "col=" singlespec 0*( ";" singlespec)
   cellsel      =  "cell=" cellspec 0*( ";" cellspec)
   singlespec   =  position [ "-" position ]
   cellspec     =  cellrow "," cellcol [ "-" cellrow "," cellcol ]
   cellrow      =  position
   cellcol      =  position
   position     =  number / "*"
   number       =  1*( DIGIT )

4.  Fragment Identifier Processing

   Applications implementing support for the mechanism described in this
   memo MUST behave as described in the following sections.

4.1.  Syntax Errors in Fragment Identifiers

   If a fragment identifier contains a syntax error (i.e., does not
   conform to the syntax specified in Section 3), then it MUST be
   ignored by clients.  Clients MUST NOT make any attempt to correct or
   guess fragment identifiers.  Syntax errors MAY be reported by
   clients.

4.2.  Semantics of Fragment Identifiers

   Rows and columns in CSV are counted from one.  Positions thus refer
   to the rows and columns starting from position 1, which identifies
   the first row or column of a CSV.  The special character "*" can be
   used to refer to the last row or column of a CSV, thus allowing
   fragment identifiers to easily identify ranges that extend to the
   last row or column.

   If single selections refer to non-existing rows or columns (i.e.,
   beyond the size of the CSV), they MUST be ignored.

   If ranges extend beyond the size of the CSV (by extending to rows or
   columns beyond the size of the CSV), they MUST be interpreted to only
   extend to the actual size of the CSV.

   If selections of ranges of rows, ranges of columns, or ranges of
   cells are specified in a way so that they select "inversely" (i.e.,
   "#row=10-5" or "#cell=10,10-5,5"), they MUST be ignored.

   Each specification of an identified region is processed
   independently, and ignored specifications (because of reasons listed
   in the previous paragraphs) do not cause the whole fragment
   identifier to fail, they just mean that this single specification is
   ignored.  For the example file, the fragment identifier
   "#row=1-2;5-4;13-16" does identify the first two rows: the second
   specification is an "inverse" specification and thus is ignored, and
   the third specification targets rows beyond the actual size of the
   CSV and thus is also ignored.

   The complete fragment identifier identifies all the successfully
   evaluated identified parts as a single identified fragment.  This
   fragment can be disjoint because of multiple selections.  Multiple
   selections also can result in overlapping individual parts, and it is
   up to the user agent how to process such a fragment and whether the
   individual parts are still made accessible (i.e., visualized in
   visual user agents) or are presented as one unit.  For example, the
   fragment identifier "#row=3-6;4-5" contains a second identified part
   that is completely contained in the first identified part.  Whether a
   user agent maintains this selection as two parts, or simply signals
   that the identified fragment spans from the third to the sixth row,
   is up for the user agent to decide.

5.  IANA Considerations

   IANA has added a reference to this specification in the text/csv
   media type registration.

5.1.  The text/csv media type

   The Internet media type [RFC6838] for a CSV document is text/csv.
   The following registration has been copied from the original
   registration of text/csv [RFC4180], with the exception of the added
   fragment identification considerations and added security
   considerations for fragment identifiers.

   Type name:  text

   Subtype name:  csv

   Required parameters:  none

   Optional parameters:  charset, header

      The "charset" parameter specifies the charset employed by the CSV
      content.  In accordance with RFC 6657 [RFC6657], the charset
      parameter SHOULD be used, and if it is not present, UTF-8 SHOULD
      be assumed as the default (this implies that US-ASCII CSV will
      work, even when not specifying the "charset" parameter).  Any
      charset defined by IANA for the "text" tree may be used in
      conjunction with the "charset" parameter.

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

   Encoding considerations:  CSV MIME entities consist of binary data
      [RFC6838].  As per Section 4.1.1. of RFC 2046 [RFC2046], this
      media type uses CRLF to denote line breaks.  However, implementers
      should be aware that some implementations may use other values.

   Security considerations:

      Text/csv consists of nothing but passive text data that should not
      pose any direct risks.  However, it is possible that malicious
      data may be included in order to exploit buffer overruns or other
      bugs in the program processing the text/csv data.

      The text/csv format provides no confidentiality or integrity
      protection, so if such protections are needed, they must be
      supplied externally.

      The fact that software implementing fragment identifiers for CSV
      and software not implementing them differs in behavior, and the
      fact that different software may show documents or fragments to
      users in different ways, can lead to misunderstandings on the part
      of users.  Such misunderstandings might be exploited in a way
      similar to spoofing or phishing.

      Implementers and users of fragment identifiers for CSV text should
      also be aware of the security considerations in RFC 3986 [RFC3986]
      and RFC 3987 [RFC3987].

   Interoperability considerations:  Due to lack of a single
      specification, there are considerable differences among
      implementations.  Implementers should "be conservative in what you
      do, be liberal in what you accept from others" (RFC 793 [RFC0793])
      when processing CSV files.  An attempt at a common definition can
      be found in Section 2.  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 of RFC 4180 [RFC4180].

   Applications that use this media type:  Spreadsheet programs and
      various data conversion utilities.

   Fragment identifier considerations:  Fragment identification for
      text/csv is supported by using fragment identifiers as specified
      by RFC 7111.

   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> and
      Erik Wilde <dret@berkeley.edu>

   Intended usage:  COMMON

   Restrictions on usage:  none

   Author:
      Yakov Shafranovich <ietf@shaftek.org> and
      Erik Wilde <dret@berkeley.edu>

   Change controller:  IESG

6.  Security Considerations

   The security considerations for text/csv fragment identifiers are
   listed in the respective section of the media type registration in
   Section 5.1.

7.  Acknowledgements

   Thanks for comments and suggestions provided by Nevil Brownlee,
   Richard Cyganiak, Ian Davis, Gannon Dick, Leigh Dodds, and Barry
   Leiba.

8.  References

8.1.  Normative References

   [RFC2045]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part One: Format of Internet Message
              Bodies", RFC 2045, November 1996.

   [RFC2046]  Freed, N. and N. Borenstein, "Multipurpose Internet Mail
              Extensions (MIME) Part Two: Media Types", RFC 2046,
              November 1996.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3986]  Berners-Lee, T., Fielding, R., and L. Masinter, "Uniform
              Resource Identifier (URI): Generic Syntax", STD 66, RFC
              3986, January 2005.

   [RFC3987]  Duerst, M. and M. Suignard, "Internationalized Resource
              Identifiers (IRIs)", RFC 3987, January 2005.

   [RFC4180]  Shafranovich, Y., "Common Format and MIME Type for Comma-
              Separated Values (CSV) Files", RFC 4180, October 2005.

   [RFC5234]  Crocker, D. and P. Overell, "Augmented BNF for Syntax
              Specifications: ABNF", STD 68, RFC 5234, January 2008.

   [RFC6657]  Melnikov, A. and J. Reschke, "Update to MIME regarding
              "charset" Parameter Handling in Textual Media Types", RFC
              6657, July 2012.

8.2.  Informative References

   [ASCII]    ANSI X3.4-1986, "Coded Character Set - 7-Bit American
              National Standard Code for Information Interchange", STD
              63, RFC 3629, 1992.

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7, RFC
              793, September 1981.

   [RFC5147]  Wilde, E. and M. Duerst, "URI Fragment Identifiers for the
              text/plain Media Type", RFC 5147, April 2008.

   [RFC6838]  Freed, N., Klensin, J., and T. Hansen, "Media Type
              Specifications and Registration Procedures", BCP 13, RFC
              6838, January 2013.

Authors' Addresses

   Michael Hausenblas
   MapR Technologies
   32 Bushypark Lawn
   Galway
   Ireland

   Phone: +353-86-0215164
   EMail: mhausenblas@maprtech.com
   URI:   http://mhausenblas.info


   Erik Wilde
   UC Berkeley

   EMail: dret@berkeley.edu
   URI:   http://dret.net/netdret/


   Jeni Tennison
   Open Data Institute
   65 Clifton Street
   London EC2A 4JE
   U.K.

   Phone: +44-797-4420482
   EMail: jeni@jenitennison.com
   URI:   http://www.jenitennison.com/blog/