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Versions: 00 01 02 03 04 05 06 07 08 RFC 7111

Network Working Group                                      M. Hausenblas
Internet-Draft                                          DERI, NUI Galway
Updates: 4180 (if approved)                                     E. Wilde
Intended status: Standards Track                             UC Berkeley
Expires: October 28, 2011                                 April 26, 2011


          URI Fragment Identifiers for the text/csv Media Type
                    draft-hausenblas-csv-fragment-00

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 cell, row, column, or
   slice.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on October 28, 2011.

Copyright Notice

   Copyright (c) 2011 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
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   described in the Simplified BSD License.



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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 . . . . . . . . . . . . . . . . 4
     2.1.  Header  . . . . . . . . . . . . . . . . . . . . . . . . . . 5
     2.2.  Row-based selection . . . . . . . . . . . . . . . . . . . . 5
     2.3.  Column-based selection  . . . . . . . . . . . . . . . . . . 5
     2.4.  Slice-based selection . . . . . . . . . . . . . . . . . . . 6
   3.  Fragment Identification Syntax  . . . . . . . . . . . . . . . . 6
   4.  Fragment Identifier Processing  . . . . . . . . . . . . . . . . 7
     4.1.  Syntax Errors in Fragment Identifiers . . . . . . . . . . . 7
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 7
   6.  Security Considerations . . . . . . . . . . . . . . . . . . . . 7
   7.  Change Log  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . . . 8
     8.1.  Normative References  . . . . . . . . . . . . . . . . . . . 8
     8.2.  Non-Normative References  . . . . . . . . . . . . . . . . . 9
   Appendix A.  Acknowledgements . . . . . . . . . . . . . . . . . . . 9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 9


























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1.  Introduction

   This memo updates the text/csv media type defined in RFC 4180 [1] by
   defining URI fragment identifiers for text/csv MIME entities.

   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 [2] and RFC 2046 [3] are used to identify different types
   and sub-types of media.  The text/csv media type is defined in RFC
   4180 [1], using US-ASCII [9] as the default character encoding (other
   character encodings can be used as well).

1.2.  Why text/csv Fragment Identifiers?

   URIs are the identification mechanism for resources on the Web. The
   URI syntax specified in RFC 3986 [4] 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 user agent after the retrieval action has been
   successfully completed.  The semantics of a fragment identifier is a
   property of the data resulting from a retrieval action, regardless of
   the type of URI used in the 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 [10], 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 the part they really are interested in or want to talk
   about, rather than always pointing to a complete resource.  Even
   though it is suggested that fragment identification methods are
   specified in a media type's MIME registration (see [11]), 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



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   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, discovery (what column
   headings or how many rows are available), selecting a part for visual
   rendering, stream processing, making assertions about a certain value
   (provenance, confidence, 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 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 [5].


2.  Fragment Identification Methods

   This memo specifies fragment identification using following methods:
   header, row, column and slice.  As of RFC 4180 [1] the header line is
   optional and hence the application of the method is dependent on the
   actual format of the text/csv MIME entity.




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   Throughout the sections below the following table in CSV 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.  Header

   For discovery purposes, the "head" scheme is used, returning the
   first row.  If the "header" parameter per RFC 4180 [1] is available
   and its value is "present" the client can reliable determine that it
   is a header.

     http://example.com/data.csv#head

   Applied to the reference table, the above CSV fragment would select
   the header row, yielding:

   date,temperature,place

2.2.  Row-based selection

   To select a specific record, the "row" scheme followed by a single
   number is used (the first record has the index 0).  If the fragment
   is given in the form row:*, then no record is selected but the
   overall number of records is returned.

     http://example.com/data.csv#row:2

   The above CSV fragment yields: while the following computes the
   number of records (which equals 6, in the reference table)

   2011-01-03,0,Galway

   The following computes the number of records (which equals 6, in the
   reference table):

     http://example.com/data.csv#row:*

2.3.  Column-based selection

   To select values from a certain column, the "col" scheme, followed
   either by a single number or the value of a header field is used.




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     http://example.com/data.csv#col:temperature

   The above CSV fragment addresses a column by name, yielding:

   1,-1,0,6,8,5

   A column can also be addressed by position as shown in the next
   example:

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

   The above CSV fragment selects the third column:

   Galway,Galway,Galway,Berkeley,Berkeley,Berkeley

2.4.  Slice-based selection

   To select a part of table, called a slice in the following, the
   "where" scheme is used.  The allowed values are a comma-separated
   list of header fields with corresponding field values in the table.

     http://example.com/data.csv#where:date=2011-01-01

   The above CSV fragment selects a slice, yielding another CSV table as
   follows:

   temperature,place
   1,Galway
   6,Berkeley


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 4234 [6],
   including the rules DIGIT and HEXDIG.  The mime-charset rule is
   defined in RFC 2978 [7].

   NOTE:  In the descriptions that follow, specified text values MUST be
      used exactly as given, using exactly the indicated lower-case
      letters.  In this respect, the ABNF usage differs from [6].









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   csv-fragment =  headersel / wheresel / colsel / rowsel
   headersel = "head"
   rowsel   = "row:" rowspec
   colsel   = "col:" colspec
   wheresel = "where:" kvpairs
   kvpairs = 1*( col "=" val 0*1(",") )
   col = 1*TEXTDATA
   val = 1*TEXTDATA
   colspec = column
   rowspec = "*" / rownum
   column = 1*TEXTDATA / 1*DIGIT
   rownum = 1*DIGIT
   TEXTDATA =  %x23-2B / %x2D-3C / %x3E-7E
   DIGIT =  %x30-39


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.


5.  IANA Considerations

   Note to RFC Editor: Please change this section to read as follows
   after the IANA action has been completed: "IANA has added a reference
   to this specification in the Text/Plain Media Type registration."

   IANA is requested to update the registration of the MIME Media type
   text/csv at http://www.iana.org/assignments/media-types/text/ with
   the fragment identifier defined in this memo by adding a reference to
   this memo (with the appropriate RFC number once it is known).


6.  Security Considerations

   The fact that software implementing fragment identifiers for plain
   text 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



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   users.  Such misunderstandings might be exploited in a way similar to
   spoofing or phishing.

   In particular, care has to be taken if fragment identifiers are used
   together with a mechanism that allows to show only the part of a
   document identified by a fragment.  One scenario may be the use of a
   fragment identifier to hide small-print legal text.  Another scenario
   may be the inclusion of site-key-like material, which may give the
   user the impression of using the real site rather than a fake
   site.Other scenarios may also be possible.  Possible countermeasures
   may include but are not limited to displaying the included content
   within clearly visible boundaries and limiting inclusion to material
   from the same security realm or from realms that give explicit
   permission to be included in another realm.

   Please note that the above issues all apply to the client side;
   fragment identifiers are not used when resolving an URI to retrieve
   the representation of a resource, but are only applied on the client
   side.

   Implementers and users of fragment identifiers for CSV text should
   also be aware of the security considerations in RFC 3986 [4] and RFC
   3987 [8].


7.  Change Log

   Note to RFC Editor: Please remove this section before publication.


8.  References

8.1.  Normative References

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

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

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

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



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

   [6]   Crocker, D. and P. Overell, "Augmented BNF for Syntax
         Specifications: ABNF", RFC 4234, October 2005.

   [7]   Freed, N. and J. Postel, "IANA Charset Registration
         Procedures", BCP 19, October 2000.

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

8.2.  Non-Normative References

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

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

   [11]  Freed, N. and J. Klensin, "Media Type Specifications and
         Registration Procedures", RFC 4288, December 2005.


Appendix A.  Acknowledgements

   Thanks for comments and suggestions provided by ...


Authors' Addresses

   Michael Hausenblas
   DERI, NUI Galway
   IDA Business Park
   Galway
   Ireland

   Phone: +353-91-495730
   Email: michael.hausenblas@deri.org
   URI:   http://sw-app.org/about.html










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   Erik Wilde
   UC Berkeley
   School of Information, 311 South Hall
   Berkeley, CA 94720-4600
   U.S.A.

   Phone: +1-510-6432253
   Email: dret@berkeley.edu
   URI:   http://dret.net/netdret/










































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