Re: Keyword extraction

Wed, 26 Nov 2008 06:07:45 -0800

Ah, yes, That is important. In lucene, the MLT will see if the term vector is stored, and if it is not it will still be able to perform the querying, but in a much much much less efficient way.. Lucene will analyze the document (and the variable DEFAULT_MAX_NUM_TOKENS_PARSED will be used to limit the number of tokens that will be parsed). (don't want to go into details on this since I haven't really dug through the code:p) But when the field isn't stored either, it is rather difficult to re-analyze the document;)
On a general note, if you want to "really" understand how the MLT works, take a look at the wiki or read this thorough blog post: http://cephas.net/blog/2008/03/30/how-morelikethis-works-in-lucene/ 

Regards,
 Aleksander


On Wed, 26 Nov 2008 14:41:52 +0100, Plaatje, Patrick  
<[EMAIL PROTECTED]> wrote:



Hi Aleksander,


This was a typo on my end, the original query included a semicolon  
instead of an equal sign. But I think it has to do with my field not  
being stored and not being identified as termVectors="true". I'm  
recreating the index now, and see if this fixes the problem.


Best,

patrick

-----Original Message-----
From: Aleksander M. Stensby [mailto:[EMAIL PROTECTED]
Sent: woensdag 26 november 2008 14:37
To: solr-user@lucene.apache.org
Subject: Re: Keyword extraction

Hi there!

Well, first of all i think you have an error in your query, if I'm not  
mistaken.

You say http://localhost:8080/solr/select/?q=id=18477975...
but since you are referring to the field called "id", you must say:
http://localhost:8080/solr/select/?q=id:18477975...
(use colon instead of the equals sign).
I think that will do the trick.

If not, try adding the &debugQuery=on at the end of your request url, to  
see debug output on how the query is parsed and if/how any documents are  
matched against your query.

Hope this helps.

Cheers,
  Aleksander




On Wed, 26 Nov 2008 13:08:30 +0100, Plaatje, Patrick  
<[EMAIL PROTECTED]> wrote:



Hi Aleksander,

Thanx for clearing this up. I am confident that this is a way to
explore for me as I'm just starting to grasp the matter. Do you know
why I'm not getting any results with the query posted earlier then? It
gives me the folowing only:

<lst name="moreLikeThis">
        <result name="18477975" numFound="0" start="0"/> </lst>

Instead of delivering details of the interestingTerms.

Thanks in advance

Patrick


-----Original Message-----
From: Aleksander M. Stensby [mailto:[EMAIL PROTECTED]
Sent: woensdag 26 november 2008 13:03
To: solr-user@lucene.apache.org
Subject: Re: Keyword extraction

I do not agree with you at all. The concept of MoreLikeThis is based

on the fundamental idea of TF-IDF weighting, and not term frequency  
alone.

Please take a look at:
http://lucene.apache.org/java/2_4_0/api/org/apache/lucene/search/simil
ar/MoreLikeThis.html As you can see, it is possible to use cut-off
thresholds to significantly reduce the number of unimportant terms,
and generate highly suitable queries based on the tf-idf frequency of
the term, since as you point out, high frequency terms alone tends to
be useless for querying, but taking the document frequency into
account drastically increases the importance of the term!

In solr, use parameters to manipulate your desired results:
http://wiki.apache.org/solr/MoreLikeThis#head-6460069f297626f2a982f1e2
2ec5d1519c456b2c
For instance:
mlt.mintf - Minimum Term Frequency - the frequency below which terms
will be ignored in the source doc.
mlt.mindf - Minimum Document Frequency - the frequency at which words
will be ignored which do not occur in at least this many docs.
You can also set thresholds for term length etc.

Hope this gives you a better idea of things.
- Aleks

On Wed, 26 Nov 2008 12:38:38 +0100, Scurtu Vitalie <[EMAIL PROTECTED]>
wrote:


Dear Partick, I had the same problem with MoreLikeThis function.

After  briefly reading and analyzing the source code of moreLikeThis
function in solr, I conducted:

MoreLikeThis uses term vectors to ranks all the terms from a document
by its frequency. According to its ranking, it will start to generate
queries, artificially, and search for documents.

So, moreLikeThis will retrieve related documents by artificially
generating queries based on most frequent terms.

There's a big problem with "most frequent terms"  from documents.
Most frequent words are usually meaningless, or so called function

words, or, people from Information Retrieval like to call them  
stopwords.

However, ignoring  technical problems of implementation of
moreLikeThis function, this approach is very dangerous, since queries
are generated artificially based on a given document.
Writting queries for retrieving a document is a human task, and it
assumes some knowledge (user knows what document he wants).

I advice to use others approaches, depending on your expectation. For
example, you can extract similar documents just by searching for

documents with similar title (more like this doesn't work in this  
case).


I hope it helps,
Best Regards,
Vitalie Scurtu
--- On Wed, 11/26/08, Plaatje, Patrick
<[EMAIL PROTECTED]>
wrote:
From: Plaatje, Patrick <[EMAIL PROTECTED]>
Subject: RE:  Keyword extraction
To: solr-user@lucene.apache.org
Date: Wednesday, November 26, 2008, 10:52 AM

Hi All,
as an addition to my previous post, no interestingTerms are returned
when i execute the folowing url:
http://localhost:8080/solr/select/?q=id=18477975&mlt.fl=text&mlt.inte
r es tingTerms=list&mlt=true&mlt.match.include=true
I get a moreLikeThis list though, any thoughts?
Best,
Patrick




























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