Re: [bdbxml] Regular expressions in bdbxml

>> It's impossible for any regular expression index to provide lookup  
>> speed close to the current index types. All they can do is  
>> dramatically lessen the set size for which the regular expression  
>> must be executed against each record. And even then, it's usually  
>> just for POSIX 1003.2 regexes, as opposed to PCRE, and  
>> implementing "multigram" indexes is not a small job.
>>
>> But, yes, this would be a nice feature. :-)
>>
>
> Right, but that's what indexing is all about, reducing the set of  
> potential matches to lower query processing time.  Here's one paper  
> we're reviewing that has an interesting approach.
>
> http://oak.cs.ucla.edu/~cho/papers/cho-regex.pdf

Yeah, the Cho solution uses multigram indexes. I only meant to say  
that these indexes often don't yield the improvement that might be  
expected, and often (not always) there are better ways to do queries  
(especially in XQuery, where you can do your own set processing).  
This depends in large part on the regex itself, of course.

And yes, I think this would be an awesome addition to BDB XML. In  
truth, this would be a great use of BDB itself: a general-purpose  
regular expression indexer. Lots of applications outside of BDB XML.

Regards,
Dan



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