MG does either boolean or ranked queries (but not both at once) while
MGPP ranks boolean queries. So the "display results in ranked/natural
order" just switches the ranking on/off.
Only documents which match the boolean query will be included in the
The ranking is done using a cosine measure (based on term frequency,
document frequency, document weights...) - see the book mentioned below
for more information about this.
There is a website about MG, at http://www.cs.mu.oz.au/mg/ and there is
a link there to more information about the software. I thought it may
have info about the ranking, but it is down at the moment. I'm not sure
if this is a permanent error, so you may like to check there.
MGPP is a reimplementation of MG which is written in C++ instead of C,
and uses word level indexing instead of document level. I think that the
compression, indexing and ranking algorithms are pretty much the same as
Michael Dewsnip wrote:
> The best source of information about the ranking done by MG (and MGPP,
> which is similar) is the "Managing Gigabytes" book, by Ian H. Witten,
> Alistair Moffat and Tim Bell.
> If you're technically inclined the cheap version is to look at the code
> and its comments :-)
> Ying-Hsang Liu wrote:
>>I am using Greenstone for an information retrieval experiment. After
>>Greenstone documentation and the following message, it is still not
>>clear to me
>>how the ranking works in Greenstone (I am using version 2.70),
>>MGPP search engine.
>>My collection is built upon MGPP. If I search the system using
>>search and choose the option "Search and display results in ranked
>>does the system work?
>>Is it a Boolean-based search with ranked output? Or, is it a ranked
>>the "Some" option search in simple form search? If either one involves
>>of search results, could I get more detailed descriptions in technical
>>Rutgers - The State University
>>School of Communication,
>>Information and Library Studies
>>4 Huntington St.
>>New Brunswick, NJ 08901
>>*Michael Dewsnip* mdewsnip at cs.waikato.ac.nz
>>/Fri Sep 26 11:39:51 NZST 2003/
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>>Thanks very much for your answer.
>>In regards to the ordering of the search results, it depends on whether a
>>boolean or ranked query is being performed. For a ranked query the search
>>results are ordered according to how closely they match the query (as you
>>would expect). For a boolean query, a document either matches or
>>there is no scope for ordering. Therefore, the documents are simply listed
>>based on the order they were indexed by MG/MGPP, as you guessed.
>>greenstone-devel mailing list
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