XOM API for Processing XML with Java

[Wolfgang Hoschek <wolfgang.hoschek AT mac.com>]

On Aug 28, 2006, at 12:16 PM, John Cowan wrote:

> Michael Kay scripsit:
>
> > I don't think there's any "should" about it. There's no moral  
> > obligation for
> > software designers to handle pathological cases well (or at all);  
> > on the
> > contrary, one has to optimize for the most common case. I don't  
> > think it's
> > unreasonable to take the view that this example is pathological.
>
> I agree, but I also would point out that the slope you are standing  
> on is
> dangerously slippery.  TagSoup used to have a fixed limit on the  
> length
> of an attribute value; now the only limit is that of a Java String  
> object,
> because I found documents in the wild with tens of thousands of  
> keywords,
> often repetitive, in title attributes.  It's one thing to handle such
> cases inefficiently, quite another to fail to handle them at all.
>
> We don't want to have parser authors claiming conformance to XML 1.0
> and then failing because parameter entities are pathological (though
> the Billion Laughs attack *is* pathological) ...

Assuming a small number of namespaces in scope at any given moment  
seems a very reasonable stance to me, based on common patterns seen  
in real world usage. I certainly woulnd't mind degradation in the  
pathologic case (large N), but I wouldn't design it to fail, by way  
of (somewhat arbitrary) static limits.

I should add that sometimes the worst-case can be handled almost as  
well as the best-case by changing the underlying data structure and  
associated algorithms, yielding more uniform run time behaviour at  
the expense of, say, 10% loss for the best-case. Optimization (and  
complexity) trade-offs regarding worst-case / best-case behaviour are  
on a case by case basis. For example, changing the NamePool from a  
fixed hash table to a form of dynamically resizable hash table (or  
having it overflow into a dynamic table for the pathologic case) may  
or may not fall into that category, I don't know.

Wolfgang.