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Changing the default value of mustUnderstand to "true"

From: Hugo Haas <hugo@w3.org>
Date: Mon, 1 Jul 2002 15:52:50 -0400
To: xmlp-comments@w3.org
Message-ID: <20020701195250.GB10808@jibboom.w3.org>


The default value of the mustUnderstand Attribute is "false"[1]:

|   The type of the mustUnderstand attribute information item is boolean
|   in the namespace "http://www.w3.org/2001/XMLSchema".
|   Omitting this attribute information item is defined as being
|   semantically equivalent to including it with a value of "false" or
|   "0".

Having a header block without mustUnderstand set to "true" allows the
SOAP node supposed to process this block to ignore it as shown in
2.7.1 Forwarding Intermediaries[2]:

|   Forwarding intermediaries MUST process the message according to the
|   SOAP processing model defined in 2.6 Processing SOAP Messages. They
|   MUST also remove from the message all SOAP header blocks targeted at
|   themselves, prior to forwarding, regardless of whether these header
|   blocks were processed or ignored.  

and in 2.6 Processing SOAP Messages[3]:

|    4. Process all header blocks targeted at the node and, in the case of
|       an ultimate SOAP receiver, the SOAP body. A SOAP node MUST process
|       all SOAP header blocks targeted at it. A SOAP node MAY choose to  
|       ignore the application level processing specified by non-mandatory
|       SOAP header blocks targeted at it.                                

The probability that somebody included a header and really wants
something to happen as a result of its processing is high. The
probability that the person doesn't care if the header is ignored is

For example, every header block used as examples in the primer[4]
(that I saw) uses env:mustUnderstand="true".

It therefore seems natural to make "true" the default value for



  1. http://www.w3.org/TR/2002/WD-soap12-part1-20020626/#soapmu
  2. http://www.w3.org/TR/2002/WD-soap12-part1-20020626/#forwardinter
  3. http://www.w3.org/TR/2002/WD-soap12-part1-20020626/#procsoapmsgs
  4. http://www.w3.org/TR/2002/WD-soap12-part0-20020626/
Hugo Haas - W3C
mailto:hugo@w3.org - http://www.w3.org/People/Hugo/ - tel:+1-617-452-2092
Received on Monday, 1 July 2002 15:52:51 UTC

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