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Re: Question regarding contrib/fulltextindexing

From: "Derek Barrett" <derekbarrett(at)graffiti(dot)net>
To: <andrew(at)catalyst(dot)net(dot)nz>
Cc: pgsql-novice(at)postgresql(dot)org
Subject: Re: Question regarding contrib/fulltextindexing
Date: 2002-07-15 03:07:42
Message-ID: 20020715030742.29286.qmail@graffiti.net (view raw or flat)
Thread:
Lists: pgsql-novice
Excellent!

This solution will work out perfectly.

The good thing is that I already have the code that does the 
noise word filter on the SELECT side, so just basically some cut
and paste there to add it to the INSERT side.

Thanks for taking the time out for the tips and for clearing that up Andrew. Golden.

Best,

Derek


----- Original Message -----
From: Andrew McMillan <andrew(at)catalyst(dot)net(dot)nz>
Date: 15 Jul 2002 11:39:12 +1200
To: Derek Barrett <derekbarrett(at)graffiti(dot)net>
Subject: Re: [NOVICE] Question regarding contrib/fulltextindexing


> On Mon, 2002-07-15 at 10:41, Derek Barrett wrote:
> > Thanks Andrew, that solution seems to be easier in my mind.
> > 
> > 
> > Okay, so I create a lookup table for the description field.
> > 
> > CREATE TABLE lookup_description (
> > 
> > pk            integer
> > id            integer 
> > search_word   varchar(50)
> > 
> > )
> > 
> > (pk is the primary key, id being a foreign key)
> > 
> > 
> > (By the way, any recommendation in sizing the search_word field? Are there strings that are large enough that aren't worth indexing?) 
> > 
> > My user INSERTS the following string:
> > 
> > "The quick brown fox jumped over the moon and another fox."
> > 
> > In my code, I use a for loop, and take the text string and put it into an array, and fill up the lookup_description table. Of course, I will create a noisewords filter to remove words like the, a, an from this list. What about duplicate words? Should those be filtered out as well? In this example, fox is duplicated. I would assume that leaving in the duplicates, might be useful later if I decide to implement a relevency-type of search engine. (Rank the results based on how many times, "fox" is found).
> > 
> > TABLE lookup_description
> > 
> > pk id search_word
> > -- -- -----------
> > 1  1  quick
> > 2  1  brown
> > 3  1  fox
> > 4  1  jumped
> > 5  1  over
> > 6  1  moon
> > 7  1  another
> > 8  1  fox
> > 
> > Then I can create an index on the search_word column. Later when I do my SELECT query, I will join this lookup query to the main query.
> > 
> > Is that the idea?
> 
> Yes, that's the basic idea.  A few points though:
> 1) the index table doesn't need a special 'primary key' field - what
> value does that add?
> 
> 2) the search_word can be defined as 'text', so you don't need to
> specify the maximum length.
> 
> 3) Realistically there is little advantage searching for words longer
> than (say) 15 characters, but they also appear very infrequently.  You
> have to ensure that your search functionality does the same sort of
> transformations to searched for words as it did when inserting words
> into the index table.  This means that if your insert truncates, or
> doesn't insert some words in a stop list (if, of, a ...) then your
> search functionality needs to do the same.
> 
> 4) I usually have a stop_list of words that don't get indexed too:
> CREATE TABLE stop_list (
>   stop_word TEXT PRIMARY KEY
> );
> I usually load this into a hash in my perl script that is doing the
> loading, but it can be more complex to deal with this appropriately in
> the actual searching code - you need a first pass through the search
> list to remove stop_list words, and a second pass to build the search
> query.
> 
> 5) you need to create an index on search_word:
> CREATE INDEX lookup_description_srch 
>         ON lookup_description ( search_word );
> 
> 
> Hope this helps,
> 					Andrew.
> -- 
> --------------------------------------------------------------------
> Andrew @ Catalyst .Net.NZ Ltd, PO Box 11-053, Manners St, Wellington
> WEB: http://catalyst.net.nz/        PHYS: Level 2, 150-154 Willis St
> DDI: +64(4)916-7201    MOB: +64(21)635-694    OFFICE: +64(4)499-2267
>        Are you enrolled at http://schoolreunions.co.nz/ yet?
> 
> 

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