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From Brendon McLean <>
Subject Re: Strategy for arbitrary predicate queries in Couchdb
Date Mon, 24 Jan 2011 15:42:50 GMT
Hi Michael,

I'm not sure how you would do that.  The predicates are non-exclusive so I'd have to literally
perform the aggregation outside of the database.  I suppose if you went this way, you could
check the document matches for each predicate, choosing the smallest set to examine outside
of the database.


On 24 Jan 2011, at 16:12 , Michael Zedeler wrote:

> On 2011-01-24 13:49, Brendon McLean wrote:
>> Our documents really only contain two types of data:
>> Numeric attributes
>> Boolean attributes
>> The boolean attributes essentially mark a document as belonging to one or more non-exclusive
sets. The numeric attributes will always only need to be summed. One way of structuring the
document is like this:
>> {
>>   "id": 3123123,
>>   "attr": {"x": 2, "y": 4, "z": 6},
>>   "sets": ["A", "B", "C"]
>> }
>> With this structure, it's easy to work out aggregate x, y, z values for the sets
A, B and C, but it gets more complicated when you want to see the aggregates for intersections
like A&C.
>> In this small case I could emit keys for all permutations of ABC ("A, B, C, AB, AC,
BC, ABC"), but I'm worried about how this will scale. Our documents could belong to some combination
of 80 sets and it is fronted by a user-interface which can construct any conceivable combination
of them.
>> I'm inclined to think that this isn't a job for a CouchDB, and perhaps MongoDB or
something else would be better suited to this problem.
> We have solved the problem for attributes by creating one index for each attribute (running
one query for each index) and then just aggregating the results after.
> Regards,
> Michael.

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