Xapian discuss - Apr 2009 - questions about valuerangeprocessor and RefCntBase(edit and send again)

Hi!  Alls

As Charlie said that my questions are hard to understand,i try to rephrase them.
Once you have time, please give me a help.

Indeed, I care more about how Xapian works.And I want to learn how  search
engine works and how to design or  optimize a search engine.

I realized that some basic concept/classes,such as RefCntBase, internal  and
Stats, are very important. But i can not make clear that why Xapian need them.In
another word, i can not find out how Xapian work with them.

For example,i see that RefCntBase is a base class for objects which Xapian
reference count,but i can not know the purpose that Xapian count reference,which
is something i still want to know.
Simply,why Xapian needs reference count ?


Another question is about ValueRangeProcessor. 
I have read this:
http://xapian.org/docs/valueranges.html

Xapian::DateValueRangeProcessor date_proc(2, true, 1930); 
qp.add_valuerangeprocessor(&date_proc); 
    these was added in my code and it works perfectly.
I input the query"20090416..20090419", and I use
query.get_description() to get the description "Parsed query is:
Xapian::Query(VALUE_RANGE 2 20090216 20090219)".

Then, i wonder that how Xapian works it out.I can't see a detailed
description of the OP_VALUE_* query operators anywhere.
Does Xapian rebuilt my query into 20090416,20090417,20090418
 20090419 and retrieval them separately ?
Or,it find start '20090416' and end '20090219' in the Btree,then
return all the documents between them?
 
In another word, How does Xapian work while search value in Btree? And what is
the difference between using value or not while search?

Generally speaking,i want to now how "valuerangesearch" works. Whether
it only search in field "Value" or not?
 

I have also read  this:
http://xapian.org/docs/matcherdesign.html
 
I can not find any word about ValueRangeProcessor, or
"ValueRangePostList".
Then, how does the PostList Tree was design with RangeProcessor?
 


Regards,

baijl
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On Tue, Apr 28, 2009 at 09:46:55PM +0800, ??? wrote:
> For example,i see that RefCntBase is a base class for objects which
> Xapian reference count,but i can not know the purpose that Xapian
> count reference,which is something i still want to know.  Simply,why
> Xapian needs reference count?
Reference counting is a technique to approach memory management in
(principally) class libraries. I suggest you look up a good reference
on modern C++ practice to get a grip on the ideas behind it. The use
of reference counting techniques in Xapian is unrelated to its search
engine & information retrieval features.
> Another question is about ValueRangeProcessor. [...] i wonder that
> how Xapian works it out.I can't see a detailed description of the
> OP_VALUE_* query operators anywhere.
I think I stated earlier that we don't have any user-level
documentation of how OP_VALUE_* work. However most of the implementation is
in (for instance) matcher/valuerangepostlist.cc, which is only 168
lines long including comments. You care most about the next() and
check() methods, but if you want to know more you'll have to get stuck
into the code for post lists and how they get used.
> I have also read  this:
> http://xapian.org/docs/matcherdesign.html
>  
> I can not find any word about ValueRangeProcessor, or
"ValueRangePostList".
> Then, how does the PostList Tree was design with RangeProcessor?
ValueRangeProcessor is only used by the QueryParser; it constructs the
relevant query using OP_VALUE_* operators to do what's needed. These
are implemented in the relevant Value*PostList class.

There's no separate documentation of how ValueRangePostList (for
instance) works; it's sufficiently small that you can read the source
to figure it out. The matcher design document explains how post lists
in general are used to build MSets.

J

-- 
  James Aylett

  talktorex.co.uk - xapian.org - uncertaintydivision.org