[SML] Whether to support Attribute or not?

Paul Tchistopolskii paul at qub.com
Mon Nov 29 23:59:01 GMT 1999

> > If you have to "dig" into the contents to figure
> > out which "processing pipeline" the content is
> > placed on then you have effectively elminated
> > all hope of sequential processing.  Thus, you
> > need random access to the information stream.
> > And hence, "large" memory requiremens, thus
> > undermining the apparant "simplicity" of SML.
> > 
> Well, I don't agree with you on this point. I have been working
> on a streaming query processor for XML for some time, and the
> problem is just not there. Why is it a problem going into the
> element one or two levels deep? Besides the chances that you will
> encode all the information relevant to the query processor into
> attributes is very small. Consider the example above with the
> local schools: what if I want to select all homes that have
> some specific school in their neighborhood? This information
> cannot be encoded in the attributes, since its nested. But I
> can still stream such queries, all I have to do is descend one
> level into each element and the find the school that satisfies
> the condition.

This is exactly the point. Attributes kludge allows easier 
processing when the hierarchy has only one level and 
*only* in this situation. 

<foo><att>Attr</att></foo>    - when processing it with SAX 
no easy way to implement the 'look-forward' rule of kind 
'If foo  has a child ( property )  Attr'

<foo att="Attr"></foo>    - when processing it with SAX
it is easy to implement the 'look-forward' rule of kind 
'If foo  has a child ( property )  Attr'

As any other kludge, attributes kludge allows you 
to process some percent of more easily than
without that klugde.

Like any other kludge even  it gives you something, 
it costs something. 

I think what it gives is not worth what  it costs.  Your mileage 
may vary, but for sure there is no logical arguments here. 

" Does this kludge simplyfy some things?  - Yes it does. 
Does it makes some other  things harder? - Yes it does."  

What is more important? 

We can only guess, because if some developer is concentrated  
only on processing some simple XML documents with SAX - 
for sure Attributes kludge is very convinient. 

Developer who tries to invent the new XQL ( with updates ;-) 
may have another point of view on this subject. 
I don't know who is closer  to the 'truth' ;-)

Not talking about the changes one should make 
to the SAX handler ( XT stylesheet e t.c. ) in the situation
when something designed to be attribute turns into element.


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