Re: phrase search

On Mon, 2008-06-02 at 19:39 +0400, Teodor Sigaev wrote:
>
> > I have attached a patch for phrase search with respect to the cvs head.
> > Basically it takes a a phrase (text) and a TSVector. It checks if the
> > relative positions of lexeme in the phrase are same as in their
> > positions in TSVector.
>
> Ideally, phrase search should be implemented as new operator in tsquery, say #
> with optional distance. So, tsquery 'foo #2 bar' means: find all texts where
> 'bar' is place no far than two word from 'foo'. The complexity is about complex
> boolean expressions ( 'foo #1 ( bar1 & bar2 )' ) and about several languages as
> norwegian or german. German language has combining words, like a footboolbar -
> and they have several variants of splitting, so result of to_tsquery('foo #
> footboolbar') will be a 'foo # ( ( football & bar ) | ( foot & ball & bar ) )'
> where variants are connected with OR operation.

This is far more complicated than I thought.

> Of course, phrase search should be able to use indexes.

I can probably look into how to use index. Any pointers on this?

> >
> > If the configuration for text search is "simple", then this will produce
> > exact phrase search. Otherwise the stopwords in a phrase will be ignored
> > and the words in a phrase will only be matched with the stemmed lexeme.
>
> Your solution can't be used as is, because user should use tsquery too to use an
> index:
>
> column @@ to_tsquery('phrase search') AND is_phrase_present('phrase search',
> column)
>
> First clause will be used for index scan and it will fast search a candidates.

Yes this is exactly how I am using in my application. Do you think this
will solve a lot of common case or we should try to get phrase search

1. Use index
2. Support arbitrary distance between lexemes
3. Support complex boolean queries

-Sushant.

>
> > For my application I am using this as a separate shared object. I do not
> > know how to expose this function from the core. Can someone explain how
> > to do this?
>
> Look at contrib/ directory in pgsql's source code - make a contrib module from
> your patch. As an example, look at adminpack module - it's rather simple.
>
> Comments of your code:
> 1)
> +#ifdef PG_MODULE_MAGIC
> +PG_MODULE_MAGIC;
> +#endif
>
> That isn't needed for compiled-in in core files, it's only needed for modules.
>
> 2)
> use only /**/ comments, do not use a // (C++ style) comments