Updates:
Keywords: mime
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.
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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
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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
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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].
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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-*
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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
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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 )
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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
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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.
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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.
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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.
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[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.
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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/
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