Re: Fragments in tsearch2 headline

On Tue, 30 Oct 2007, Catalin Marinas wrote:

> On 30/10/2007, Richard Huxton <dev(at)archonet(dot)com> wrote:
>> Oleg Bartunov wrote:
>>> Catalin,
>>>
>>> what is your need ? What's wrong with this ?
>>>
>>> postgres=# select ts_headline('1 2 3 4 5 3 4 abc abc 2 3
>>> xyz','2'::tsquery, 'StartSel=...,StopSel=...')
>>> ;
>>> ts_headline
>>> -------------------------------------------
>>> 1 ...2... 3 4 5 3 4 abc abc ...2... 3 xyz
>>
>> I think he want's something like: "1 2 3 ... abc 2 3 ..."
>>
>> A few characters of context around each match and then ... between. Kind
>> of like grep -C.
>
> That's pretty much correct (with the difference that I'd like context
> of words rather than lines as in "grep" and StartSel=<b>,
> StopSel=</b>).
>
> Since the text I want a headline for might be pretty long (tens of
> lines), I'd like to only show the excerpts around the matching words.
> Similar to the above example:
>
> select ts_headline('1 2 3 4 5 3 4 abc x y z 2 3', '2 & abc'::tsquery);
>
> should give:
>
> '1 <b>2</b> 3 4 ... 3 4 <b>abc</b> x y'
>
> Currently, if you limit the maximum words so that 'abc' is too far, it
> only highlights the first match.

ok, then you have to formalize many things - how long should be excerpts,
how much excerpts to show, etc. In tsearch2 we have get_covers() function,
which produces all excerpts like:

=# select get_covers(to_tsvector('1 2 3 4 5 3 4 abc x y z 2 3'), '2&3'::tsquery);
get_covers
------------------------------------------------
1 {1 2 3 }1 4 5 {2 3 4 abc x y z {3 2 }2 3 }3
(1 row)

Once you formalize your requirements, you can look on it and adapt to your
needs (and share with people). I think it could be nice contrib module.

>
> Many of the search engines (including google) show the headline this
> way. I think Lucene can do this as well but I've never used it to be
> sure.
>
>

Regards,
Oleg
_____________________________________________________________
Oleg Bartunov, Research Scientist, Head of AstroNet (www.astronet.ru),
Sternberg Astronomical Institute, Moscow University, Russia
Internet: oleg(at)sai(dot)msu(dot)su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83