[Xapian-tickets] [Xapian] #557: Allow subqueries to use separate weighting schemes

[Xapian]

#557: Allow subqueries to use separate weighting schemes
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 Reporter:  richard      |             Owner:  olly
     Type:  enhancement  |            Status:  closed
 Priority:  normal       |         Milestone:
Component:  Library API  |           Version:
 Severity:  normal       |        Resolution:  wontfix
 Keywords:               |        Blocked By:
 Blocking:               |  Operating System:  All
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Changes (by olly):

 * status:  new => closed
 * resolution:   => wontfix


Comment:

 We've just been discussing this on IRC.

 Technically this should be possible to implement, but I'm dubious that
 adding together weights from different weighting formulae is useful in
 general - weighting schemes produce weights for terms which ought to
 produce a useful outcome when added together, but only within a weighting
 scheme - e.g. ranking computers by {{{cpu_speed + disk_size}}} is unlikely
 to make sense even if you think {{{cpu_speed}}} and {{{disk_size}}} are
 useful rankings by themselves (but to continue the analogy you can
 usefully rank by the sum of {{{disk_size}}} across multiple disks).

 In the social network example, the second weighting scheme would need to
 be one carefully tailored to fit with the main weighting scheme, so being
 able to reuse existing Weight subclasses isn't a consideration here, and I
 think that will be true in general.  I think this example could be
 addressed well with a !PostingSource subclass, and I suspect that's true
 more generally.

 So I think we should close this as wontfix, unless we can come up with a
 scenario where it is actually a better approach than !PostingSource.

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Ticket URL: <http://trac.xapian.org/ticket/557#comment:1>
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