W3C home > Mailing lists > Public > www-html-editor@w3.org > April to June 1998

Re: Possible misuse of idempotent in HTML 4.0 December para 17.13.1

From: Ian B. Jacobs <ij@w3.org>
Date: Wed, 01 Apr 1998 10:01:44 -0500
Message-ID: <352256D8.29FDF5D1@w3.org>
To: David J Woolley <djw@bts.co.uk>
CC: www-html-editor@w3.org, connolly@w3.org
David J Woolley wrote:
> 17.13.1 Form submission method
> The method attribute of the FORM element specifies the HTTP method used to send the form to the
> processing agent. This attribute may take two values:
> get: With the HTTP "get" method, the form data set [p.233] is appended to the URI specified by
> the action attribute and this new URI is sent to the processing agent.
> post: With the HTTP "post" method, the form data set [p.233] is included in the body of the form
> and sent to the processing agent.
> The "get" method should be used when the form is idempotent (i.e., causes no side-effects). Many
>                                                  ^^^^^^^^^^
>    This is not my understanding of idempotent, and I believe the parenthesized definition
>    better matches the intended meaning.
>    I understand idempotent to mean that a repeat of the operation results in no further
>    change, but that the first use may produce side effects.  I.e set the thermostat to 20
>    degrees C is idempotent, turn it up 5 degrees is not, and tell me what it is set to
>    is the sort of operation that can safely be done with GET.
> database searches have no visible side-effects and make ideal applications for the "get" method.

Hello David,

Thank you for the comment. I borrowed the term and 
the text from the HTML 2.0 specification (see [1], section 8.2.2).

In attempt to better understand "idempotent", I looked in my
American Heritage Dictionary (Third Edition), but they don't list
the word. I then checked in the Webster's Dictionary (online) and found:

  "relating to or being a mathematical quantity which is not zero and
   which when applied to itself under a given binary operation (as
   equals itself; also: relating to or being an operation
   under which a mathematical quantity is idempotent"

Does this definition of idempotent correspond to your understanding?

 - Ian

[1] ftp://ds.internic.net/rfc/rfc1866.txt
Ian Jacobs / 401 Second Ave. #19G / New York, NY 10010 USA
Tel/Fax: (212) 684-1814          Email: jacobs@w3.org
Received on Wednesday, 1 April 1998 10:02:21 UTC

This archive was generated by hypermail 2.3.1 : Wednesday, 7 January 2015 15:08:20 UTC