When is an attribute an attribute?

[len bullard]

Roy Tennant wrote:
> 
> I've been trying to figure this out for a while with no success. It seems
> to me that there are several quite different ways one can encode
> information in XML. Are all of the following correct? 

Yes.

> When and why would
> you choose one over another? Does it matter? Thank you for your indulgence
> as I puzzle out what must surely be readily apparent to most of you.

Ok, a DTD really helps this sort of discussion along, but 
FWIW:
 
> Example 1:
> ---------
> 
> <BOOK TITLE="The Call of the Wild" AUTHOR="London, Jack"\>

Use empty elements and attributes for tag bags, basically, 
if the datum has no frequency and order requirements (only 
occurs once somewhere in the attribute list). 

NOTE:  I haven't looked to see if XML dropped the 
SGML restriction on repeated values in attlist 
decls.

 
> Example 2:
> ---------
> 
> <BOOK AUTHOR="London, Jack">The Call of the Wild</BOOK>

Use this if you don't care that the string inside the 
tags is only differentiated by the BOOK, that is, 
semantically, there is no difference between this 
and 

<BOOK AUTHOR="London, Jack">Love that Wolf!!</BOOK>

or IOW, your application has to know that is a title.

 
> Example 3:
> ---------
> 
> <BOOK>
>    <TITLE>The Call of the Wild</TITLE>
>    <AUTHOR>London, Jack</AUTHOR>
> </BOOK>

Use this when it is important to know there 
is a title and author (i.e, this BOOK 
HAS-A TITLE, HAS-A AUTHOR; the 
string, The CALL of the WILD IS-A TITLE).  
Given the element type declaration, you can tell which order 
they should come in, are there multiple 
authors, are there alternate titles, etc. 
The semantic is application dependent.  For 
a linking semantic, you might be counting 
nodes inside the BOOK.  For rendering, 
you might be assigning the font value 
based on the context of the book element.
 
len

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