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Re: Equality tests on DOM nodes

From: Stephen R. Savitzky <steve@rsv.ricoh.com>
Date: 11 Dec 1998 11:07:19 -0800
To: www-dom@w3.org
Message-ID: <qck8zyts47.fsf@congo.crc.ricoh.com>
"Andrew M. Kuchling" <akuchlin@cnri.reston.va.us> writes:

> With reference to the Python DOM implementation, someone has raised
> the question of testing the equality of nodes.  I don't think there's
> anything in the DOM Recommendation that discusses this question,
> possibly because the issue doesn't raise its head in Java.

There are actually six equivalance relations that are useful for DOM nodes;
the first four apply to objects in general:

identity	two objects are identical if they have the same object ID. 
		Java, C++ ==; LISP eq

equality	two objects are equal if they have the same class and the
		values of all attributes and content are recursively equal.
		LISP equal

equivalence	two objects are equivalent if they are either identical or
		both equal and immutable.  Equivalence is permanent; if two
		objects are equivalent, nothing the program does can make
		them unequal.  
		Java equal (Java require that equal objects have the same
			    hash code)

lexical equality  two objects are lexically equal if they have the same
		  external (string) representation.  It is also useful to
		  make lexical comparisons for greater and less as well. 

similarity	two nodes are similar if they are equal, or if they have the
		same node type and their names and contents are recursively
		similar.  In DOM terms, they have the same structure, but
		they may differ in their attributes.  This is useful for,
		e.g., comparing the text of two pages from different

textual equality  two nodes are textually equal if they are lexically equal
		  after removing all markup and expanding all (defined)

 Stephen R. Savitzky   Chief Software Scientist, Ricoh Silicon Valley, Inc., 
<steve@rsv.ricoh.com>                            California Research Center
 voice: 650.496.5710   fax: 650.854.8740    URL: http://rsv.ricoh.com/~steve/
  home: <steve@starport.com> URL: http://www.starport.com/people/steve/
Received on Friday, 11 December 1998 14:03:00 UTC

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