Re: [Boost-users] [Multi-Index] New "hierarchical" indexing?

Subject: Re: [Boost-users] [Multi-Index] New "hierarchical" indexing?
From: joaquin_at_[hidden]
Date: 2009-07-14 02:18:02

Dominique Devienne escribió:
> I'm currently using hashed indices only. Does the technique of using a
> compatible key extend to them? (I suspect not in this case, but I
> thought I'd ask, just in case I'm misunderstanding.)
>   

No, it doesn't extend to hashed indices, you have to stick with ordered 
ones. The
crucial fact upon which the parent/children sorting criteria relies is 
that sorting on
scenario_t induces a lexicographical order that lists subtrees together 
(if you think of
paths as forming a directory tree, lexicographical order is equivalent 
to inorder traversal).

>> What is this? parent_t is just a sort of alias to scenario_t that
>> allows us to differentiate between a "terminal" scenario and
>> a scenario used for purposes of recursive lookup. children
>> is a compatible (with the order of entry_container_t) compare
>> predicate that levels off scenario paths in a way that, for
>> instance, if we have parent "a" then "a/b", "a/d", "a/b/e" etc.
>> are deemed equivalent to the parent.
>>     
>
> I was thinking about such a Materialized Path impl, after reading
> http://www.dbazine.com/oracle/or-articles/tropashko4 recently. But I
> would not have been able to express it in an example as easily as you
> could. I appreciate the leg up.
>
>   

I've only taken a cursory look at the reference you provide, but seems 
indeed
that my proposal basically implements the materialized path idea.

>> Is this of any help to your particular problem?
>>     
>
> I think it does. I'll need time to digest and adapt it, but it sounds
> like Materialized Path with an ordered index will avoid a full scan.
>   

Good luck with your project,

Joaquín M López Muñoz
Telefónica, Investigación y Desarrollo