[SML] Whether to support Attribute or not?

[Joe Lapp]

This argument doesn't work for me.  An XML document contains no behavior,
only data.  The XML spec gives you two syntaxes for representing data -- a
short one (attributes) and a long one (element content).  Data can be
structured in one syntax but not in the other.

A better argument for providing a replacement is the (unresolved) need to
map to and from XML.

At 04:21 AM 11/28/1999 -0500, Clark C. Evans wrote:
>On Fri, 26 Nov 1999, Don Park wrote:
>> I believe it is now time to address the question of
>> whether Attribute should be supported in SML or not.
>
>Summary:
>
>  Attributes cannot be eliminated without 
>  providing a suitable replacement.
>
>Discussion:
>
>  The reason why SGML/XML/SML is so powerful is
>  that it accurately reflects the dual nature
>  of reality.  Code has two aspects -- it is 
>  edited as data and run as instructions.
>
>  This pattern is recursive.  Witness yet another
>  compiler ("yacc"), it is code which instructs the 
>  generation of code.  
>
>  XML is powerful beacuse it recognizes that there are 
>  _always_ two simotanenous contexts that must be
>  distinguished:  data and markup.  
>
>  Attributes are the result of applying this same 
>  pattern recursively on the markup itself.   Thus, a 
>  given tag can have instructions (the attribute) and 
>  data for those instructions (the attribute's value).   
>  
>  Attributes therefore, allow a second order approximation
>  to the recursive pattern:
>
>                           [Attribute]
>                        /               
>               [Markup]
>            /           \\ 
>           /               [Value] 
>
>  [Document]                            
>                                    /  [Attribute] 
>           \\              [Markup] 
>            \\           /          \\ [Value]
>               [Content]  
>                        \\
>                           [Content]   ...
>                       
>
>  Unfortunately, as pointed out on this list many, many 
>  times -- by having a different syntax, attributes do
>  not allow for further recursion.  Thus, there is an
>  entire realm of reality which cannot be described 
>  using XML, since attributes cannot have children.
>
>  Thus, I really doubt that it is possible to have
>  a meaningful markup language without attributes --
>  however, finding a recursive replacement would 
>  be very good.
>
>  Consider:   
>    
>    <element att="val"> <content/> </element>
>
>    If attributes were eliminated, this would be mapped to:
>    
>    <element> <att>val</att> <content/> </element>
>
>  
>  Possibility #1:
>
>    Use a hard-coded namespace,
>
>    <element> <attribute:att>val</attribute:att> <content/> </element>
>    
>  Possibility #2:
>   
>    Use a marker,
>
>    <element> <$att>val</$att> <content/> </element>
>
>  Possibility #3:
>
>    Use another type of brackets,
>
>    <element> {att}val{/att} <content/> </element>
>
>  Possibility #4:
>
>    Use a divider,
>
>    <element> <att>val</att> <|> <content/> </element>
>  
>
>  In any case, replacing the attribute mechanism with
>  one that allows for recursion would allow for
>  stuff like:
>
>   <para alt="<b>alt</b>"> para </para>
>
>  To be legally expressed (using syntax #4):
>
>   <para> <alt><b>alt</b></alt> <|> para </para>
>
>
>Hmm.  Thoughts? 
>
>Clark
>  
>
>  
>
>
>
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--
Joe Lapp              (Looking for some good people to help design
Senior Engineer        and build the Internet's business-to-business
webMethods, Inc.       XML infrastructure.  We are 100% Java.)
jlapp at webMethods.com           http://www.webMethods.com

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