Yes, I totally understand, and agree. MoreLikeThis uses TF-IDF to rank terms, then it generates queries based on top ranked terms. In any case, I wasn't able to make it work after many attempts.
Finally, I've used a different method for queries generation, and it works better, or at least gives some results, while with moreLikeThis results were poor or no result at all. To mention that my index was composed by short length documents, therefore the intersection between top ranked terms by TF-IDF was empty set. MoreLikeThis works better when you have long documents. Yes, I've changed the thresholds for min TFIDF and max TFIDF, and others parameters. I've also used "mlt.maxqt" parameter to increase the number of terms used in queries generation, but still didn't work well, since the method of queries generation based on terms with the highest TF-IDF score doesn't generate representative query for document. I wasn't able to tune it. For a low value such as mlt.maxqt=3,4, results were poor, while for mlt.maxqt=5,6>>> it gave too many and irrelevant results. Thank you, Best Wishes, Vitalie Scurtu --- On Wed, 11/26/08, Aleksander M. Stensby <[EMAIL PROTECTED]> wrote: From: Aleksander M. Stensby <aleksander. [EMAIL PROTECTED]> Subject: Re: Keyword extraction To: solr-user@lucene.apache.org Date: Wednesday, November 26, 2008, 1:03 PM 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/similar/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-6460069f297626f2a982f1e22ec5d1519c456b2c 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.interes > tingTerms=list&mlt=true&mlt.match.include=true > I get a moreLikeThis list though, any thoughts? > Best, > Patrick > > > > --Aleksander M. Stensby Senior software developer Integrasco A/S www.integrasco.no
