As I understand it, the way that BASIS does phrase searching is based on first parsing the base text to "context units" (sentences and/or paragraphs) and then calculating position for tokens within those context units. That is, a token might have position 3 in context unit 4. All of this is stored in the index. There are then multiple operators: phrase any (any token in the query is matched in a context unit), phrase all (all tokens in the query match within a context unit), phrase is (all tokens match in order including any stop words), phrase like ( as for phrase is but with stop words only being position holders). There is also an "includes" operator which supports queries such as: includes "foo" & "bar" within 3 words or includes "foo" & "bar" within 3 sentences All of these plus hit highlighting are supported without reparsing the original text (which might be gigabytes); just using the information in the index. Things like thesaurus expansion in queries are handled by adding AND/OR constructs. All operators support wild cards in query terms. HTH, Stephen On Saturday 23 February 2008 21:48, Oleg Bartunov wrote: > On Sat, 23 Feb 2008, Stephen Davies wrote: > > As it turns out, all I needed was in the doco but the key element - the > > first config arg to ts_headline - was not in any of the examples so I > > missed it. > > aha, Original one were based on default > configuration, but then concept was changed, but the examples were not > modified. > > > Would it be possible for ts_headline to work with the pre-parsed > > ts_vector? > > it's impossible, Richard already explained you the reasons. > > > I see references to future plans for phrase searching in ts. Is there a > > date for this? > > Not yet. The problem mostly algebraical :) Simple 'exact search' is doable, > but we need something more, since we support boolean operators, > pluggable dictionaries (which could produce several lexemes, for example), > and document structure (lexem weights). So, we need to define consistent > algebra for text, to have predictable results. This is quite a complex > task, which require a lot of dedicated time, which we don't have. > > > Cheers and thanks, > > Stephen > > Davies > > > > On Friday 22 February 2008 22:54, Oleg Bartunov wrote: > >> On Fri, 22 Feb 2008, Stephen Davies wrote: > >>> Hmmmm! > >>> I think I now understand the ts position better, thank you. > >>> > >>> Part of my problem has been that I am used to the functionality of Open > >>> Text's LCS (aka BASIS) product which handles text differently. > >>> > >>> It includes the position (and context) information in the index and > >>> does "remember" how the text was parsed so does not need to reparse to > >>> insert hit navigation tags nor need pointers as to how to parse > >>> queries. (It also supports phrase searching.) > >>> > >>> Now that I have a better understanding of ts, I think I will be able to > >>> make it do at least most of what I hoped for. > >> > >> I'm wondering if it was not described in the text search documentation > >> :) > >> > >>> Thank you again for your help with this. > >>> > >>> Cheers, > >>> Stephen Davies > >>> > >>> On Friday 22 February 2008 20:45, Richard Huxton wrote: > >>>> Stephen Davies wrote: > >>>>> Unfortunately, my link to the box with the test database is down due > >>>>> to lack of maintenance by our local telco (Telstra) but I think that > >>>>> I also missed the optional config arg to ts_headline. > >>>>> > >>>>> The lack of link also means that I cannot confirm your findings but > >>>>> your logic looks good. > >>>> > >>>> Looks like ALTER DATABASE SET default_text_config='english' is what > >>>> you need. > >>>> > >>>>> It begs the question, however, as to why ts-headline needs to reparse > >>>>> the raw text. > >>>> > >>>> It needs to line up tsvector lexemes with actual characters in the > >>>> text. The tsvector is missing punctuation, any stopwords (the, it, a) > >>>> as well as being stemmed (if your dictionary does that). > >>>> > >>>> Also, it's looking for a short span of words that provide the best > >>>> match. That might not be a complete match of course, and is different > >>>> to how you'd normally look to use a tsvector. > >>>> > >>>>> At least in my case, I am using a trigger to parse the combination of > >>>>> Title and Abstract to a ts_vector field in the table row (as > >>>>> suggested in 12.2.2 and 12.4.3 in the doco) so that the ts_vector is > >>>>> already available to ts_headline. > >>>>> > >>>>> If ts_headline had the ability to use that pre-parsed ts_vector, my > >>>>> problem would never have arisen - and the performance of ts_headline > >>>>> would be improved. > >>>> > >>>> Maybe. It would still have to parse the text to some degree though, > >>>> just to get the original words & punctuation into the headline. > >> > >> Regards, > >> Oleg > >> _____________________________________________________________ > >> Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru), > >> Sternberg Astronomical Institute, Moscow University, Russia > >> Internet: oleg@xxxxxxxxxx, http://www.sai.msu.su/~megera/ > >> phone: +007(495)939-16-83, +007(495)939-23-83 > > Regards, > Oleg > _____________________________________________________________ > Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru), > Sternberg Astronomical Institute, Moscow University, Russia > Internet: oleg@xxxxxxxxxx, http://www.sai.msu.su/~megera/ > phone: +007(495)939-16-83, +007(495)939-23-83 -- ======================================================================== This email is for the person(s) identified above, and is confidential to the sender and the person(s). 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