XML query engines: was RE: Is XML dead already or what?

[Jarle Stabell]

Borden, Jonathan  wrote:

> 	The problem with a straight relational approach is that we need to model
> containment and heirarchies... in SQL terms this means joins, perhaps
> multilevel joins when documents are deep.

There exists a neat trick which enables simple SQL-Select queries answering 
for two given nodes, whether one is a subnode of the other, and also how 
many levels deep, in constant time, assuming you do some simple 
preprocessing on the structure. (Assigning two integers to each node in the 
tree).

I don't know who "invented" this trick, but I know that Joe Celko has 
written about it, perhaps he first described it.

Cheers,

Jarle Stabell
Digital Logikk AS


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