ts_headline

Stephen Davies wrote:

I am a bit puzzled by the output of ts_headline (V8.3) for different queries.

It seems that the difference is in the number of occurrences of the criterion
words. If the number of hits is less than some number, the ts_headline result
is "correct" but if the number of hits exceeds that limit, the result is just
the first MinWords of the "document".

I have seen cases with up to 20 hits succeed but cases with 35 hits miss.
The spread of hits does not seem to be relevant.

http://www.postgresql.org/docs/8.3/static/textsearch-controls.html#TEXTSEARCH-HEADLINE

Are you bumping into the MaxWords limit? If you've got 35 hits that must
be at least 35 words.

--
Richard Huxton
Archonet Ltd

G'day Richard.

I don't think so. A sample command is:

ts_headline(abstract,to_tsquery('english','database'),'minWords = 99, maxWords
= 999')

I have also tried with smaller maxwords without any visible effect.

Cheers,
Stephen

On Thursday 21 February 2008 19:19, Richard Huxton wrote:

Stephen Davies wrote:

I am a bit puzzled by the output of ts_headline (V8.3) for different
queries.

It seems that the difference is in the number of occurrences of the
criterion words. If the number of hits is less than some number, the
ts_headline result is "correct" but if the number of hits exceeds that
limit, the result is just the first MinWords of the "document".

I have seen cases with up to 20 hits succeed but cases with 35 hits miss.
The spread of hits does not seem to be relevant.

http://www.postgresql.org/docs/8.3/static/textsearch-controls.html#TEXTSEAR
CH-HEADLINE

Are you bumping into the MaxWords limit? If you've got 35 hits that must
be at least 35 words.

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Stephen Davies wrote:

G'day Richard.

I don't think so. A sample command is:

ts_headline(abstract,to_tsquery('english','database'),'minWords = 99, maxWords
= 999')

I have also tried with smaller maxwords without any visible effect.

Hmm - a simple test seems to work OK.

SELECT ts_headline( repeat('apple banana carrot ', 100),
to_tsquery('apple'));
ts_headline
----------------------------------------------------------------------------------------------------------------------------------------
<b>apple</b> banana carrot <b>apple</b> banana carrot <b>apple</b>
banana carrot <b>apple</b> banana carrot <b>apple</b> banana carrot
(1 row)

It's not just the start of the text either:

SELECT ts_headline( repeat('elephant ', 100) || repeat('apple banana
carrot ', 100), to_tsquery('apple'));
ts_headline
----------------------------------------------------------------------------------------------------------------------------------------
<b>apple</b> banana carrot <b>apple</b> banana carrot <b>apple</b>
banana carrot <b>apple</b> banana carrot <b>apple</b> banana carrot
(1 row)

Can you provide a piece of text that shows the problem?

--
Richard Huxton
Archonet Ltd

Attached is the "document" in question.

Searches for "norwegian", "thesaurus" and "statement" give good results. A
search for "database" gives the plain text from the beginning.

Cheers and thanks,
Stephen Davies

On Thursday 21 February 2008 20:08, Richard Huxton wrote:

Stephen Davies wrote:

G'day Richard.

I don't think so. A sample command is:

ts_headline(abstract,to_tsquery('english','database'),'minWords = 99,
maxWords = 999')

I have also tried with smaller maxwords without any visible effect.

Hmm - a simple test seems to work OK.

SELECT ts_headline( repeat('apple banana carrot ', 100),
to_tsquery('apple'));
ts_headline
---------------------------------------------------------------------------
------------------------------------------------------------- <b>apple</b>
banana carrot <b>apple</b> banana carrot <b>apple</b> banana carrot
<b>apple</b> banana carrot <b>apple</b> banana carrot (1 row)

It's not just the start of the text either:

SELECT ts_headline( repeat('elephant ', 100) || repeat('apple banana
carrot ', 100), to_tsquery('apple'));
ts_headline
---------------------------------------------------------------------------
------------------------------------------------------------- <b>apple</b>
banana carrot <b>apple</b> banana carrot <b>apple</b> banana carrot
<b>apple</b> banana carrot <b>apple</b> banana carrot (1 row)

Can you provide a piece of text that shows the problem?

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Stephen Davies wrote:

Attached is the "document" in question.

Searches for "norwegian", "thesaurus" and "statement" give good results. A
search for "database" gives the plain text from the beginning.

Seems OK here - might need to look at your configuration settings.
http://www.postgresql.org/docs/8.3/static/textsearch-debugging.html

I'll make sure I've got a clean setup here and re-run the test.

SELECT ts_headline(t, to_tsquery('database')) FROM tsearch_test;
ts_headline
-------------------------------------------------------------------------------------------------------
<b>database</b> (using a 2 KB page) to a Large File Support (LFS)
<b>database</b> (using an 8 KB page
(1 row)

--
Richard Huxton
Archonet Ltd

Interesting. I hadn't seen that section before.

As I said in my original post: "Is this a bug or am I missing some
configuration option".

I shall investigate the stuff in 12.8.
Any suggestions as to where to start?

Thanks,
Stephen Davies

On Thursday 21 February 2008 20:50, Richard Huxton wrote:

Stephen Davies wrote:

Attached is the "document" in question.

Searches for "norwegian", "thesaurus" and "statement" give good results.
A search for "database" gives the plain text from the beginning.

Seems OK here - might need to look at your configuration settings.
http://www.postgresql.org/docs/8.3/static/textsearch-debugging.html

I'll make sure I've got a clean setup here and re-run the test.

SELECT ts_headline(t, to_tsquery('database')) FROM tsearch_test;
ts_headline
---------------------------------------------------------------------------
---------------------------- <b>database</b> (using a 2 KB page) to a Large
File Support (LFS) <b>database</b> (using an 8 KB page
(1 row)

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Stephen Davies wrote:

Interesting. I hadn't seen that section before.

As I said in my original post: "Is this a bug or am I missing some
configuration option".

I shall investigate the stuff in 12.8.
Any suggestions as to where to start?

Well, no-one has been using 8.3 for more than a few weeks, so I don't
think anyone has a lot of experience with it.

I'm getting to_tsquery('database') stemming to "databas" and
to_tsvector(<your text>) gives me the following for that token:

'databas':305,630,642,663,698,719,746,870,872,951,961,974,993,1034,1042,1159,1217,1223,1238,1244,1265,1343,1357,1399,1434,1758,1818,1821,1834,2212,2240,2258,2278,2389,2529

--
Richard Huxton
Archonet Ltd

I just spotted the difference between your test and mine.

My query says:

select ts_headline(abstract,to_tsquery('english','database'),'minWords = 99,
maxWords = 999') from document where id=21;

where your equivalent does not include the 'english' arg.

If I take out the 'english' from this query, I get the same result as you.

However, the following returns zero rows:

select title,author,ts_headline(abstract,to_tsquery('database') from document
where clob @@ to_tsquery('database')

It gets more interesting:

select title,author,ts_headline(abstract,to_tsquery('database') from document
where clob @@ to_tsquery('english','database')

returns the "correct" result - one row with the expected headline.

select title,author,ts_headline(abstract,to_tsquery('english','thesaurus')
from document where clob @@ to_tsquery('english','thesaurus')

also returns the "correct" result.

I suggest that the above indicates a bug somewhere.

Cheers and thanks,
Stephen Davies

On Thursday 21 February 2008 20:50, Richard Huxton wrote:

Stephen Davies wrote:

Attached is the "document" in question.

Searches for "norwegian", "thesaurus" and "statement" give good results.
A search for "database" gives the plain text from the beginning.

Seems OK here - might need to look at your configuration settings.
http://www.postgresql.org/docs/8.3/static/textsearch-debugging.html

I'll make sure I've got a clean setup here and re-run the test.

SELECT ts_headline(t, to_tsquery('database')) FROM tsearch_test;
ts_headline
---------------------------------------------------------------------------
---------------------------- <b>database</b> (using a 2 KB page) to a Large
File Support (LFS) <b>database</b> (using an 8 KB page
(1 row)

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Stephen Davies wrote:

I just spotted the difference between your test and mine.

My query says:

select ts_headline(abstract,to_tsquery('english','database'),'minWords = 99,
maxWords = 999') from document where id=21;

where your equivalent does not include the 'english' arg.

If I take out the 'english' from this query, I get the same result as you.

What does this give you:
show default_text_search_config;
I get pg_catalog.english and the same result for the query whether I use:
to_tsquery('english','database')
or to_tsquery('pg_catalog.english','database')

Could you be picking up a bad "english" configuration (see \dF)?

However, the following returns zero rows:

select title,author,ts_headline(abstract,to_tsquery('database') from document
where clob @@ to_tsquery('database')

I take it "clob" matches "abstract"?

It gets more interesting:

select title,author,ts_headline(abstract,to_tsquery('database') from document
where clob @@ to_tsquery('english','database')

returns the "correct" result - one row with the expected headline.

Now that *is* strange. ts_headline() works without specifying 'english'
but the actual search works the other way.

select title,author,ts_headline(abstract,to_tsquery('english','thesaurus')
from document where clob @@ to_tsquery('english','thesaurus')

also returns the "correct" result.

I suggest that the above indicates a bug somewhere.

Could be - it'd be good to rule out a bad config. You might have an
unexpected list of stopwords or similar.

Let's try:
SELECT ts_debug('the database and thesaurus');
SELECT ts_debug('english', 'the database and thesaurus');
SELECT ts_debug('pg_catalog.english', 'the database and thesaurus');
I'd expect "the", "and" to be stripped out as stopwords and the other
two to get through (database stemmed to "databas").

--
Richard Huxton
Archonet Ltd

OK. The first level explanation is that my default config is "simple".
This explains the different query results as "english" reduces "database" to
"databas" while "simple does not reduce it at all.

The "document" is parsed/indexed using "english" explicitly so my queries nedd
to be explicit also (not an issue as all "real" queries are generated rather
than typed).

However, I still cannot see a reason for the ts_headline results. If anything,
they should be the other way around.

I suspect that ts_headline may only work properly when no configuration is
specified - regardless of the default setting.

Cheers,
Stephen

On Thursday 21 February 2008 22:30, Richard Huxton wrote:

Stephen Davies wrote:

I just spotted the difference between your test and mine.

My query says:

select ts_headline(abstract,to_tsquery('english','database'),'minWords =
99, maxWords = 999') from document where id=21;

where your equivalent does not include the 'english' arg.

If I take out the 'english' from this query, I get the same result as
you.

What does this give you:
show default_text_search_config;
I get pg_catalog.english and the same result for the query whether I use:
to_tsquery('english','database')
or to_tsquery('pg_catalog.english','database')

Could you be picking up a bad "english" configuration (see \dF)?

However, the following returns zero rows:

select title,author,ts_headline(abstract,to_tsquery('database') from
document where clob @@ to_tsquery('database')

I take it "clob" matches "abstract"?

It gets more interesting:

select title,author,ts_headline(abstract,to_tsquery('database') from
document where clob @@ to_tsquery('english','database')

returns the "correct" result - one row with the expected headline.

Now that *is* strange. ts_headline() works without specifying 'english'
but the actual search works the other way.

select
title,author,ts_headline(abstract,to_tsquery('english','thesaurus') from
document where clob @@ to_tsquery('english','thesaurus')

also returns the "correct" result.

I suggest that the above indicates a bug somewhere.

Could be - it'd be good to rule out a bad config. You might have an
unexpected list of stopwords or similar.

Let's try:
SELECT ts_debug('the database and thesaurus');
SELECT ts_debug('english', 'the database and thesaurus');
SELECT ts_debug('pg_catalog.english', 'the database and thesaurus');
I'd expect "the", "and" to be stripped out as stopwords and the other
two to get through (database stemmed to "databas").

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Stephen Davies wrote:

OK. The first level explanation is that my default config is "simple".

Aha! Actually, that's the whole explanation.

This explains the different query results as "english" reduces "database" to
"databas" while "simple does not reduce it at all.

Exactly.

The "document" is parsed/indexed using "english" explicitly so my queries nedd
to be explicit also (not an issue as all "real" queries are generated rather
than typed).

Or change your default configuration to match the one you're using.

However, I still cannot see a reason for the ts_headline results. If anything,
they should be the other way around.

I suspect that ts_headline may only work properly when no configuration is
specified - regardless of the default setting.

No. What's happening is that your tsvector representation of the
document (which gets indexed) contains lexemes processed by your
"english" config. So, it will have something like:
... databas: 123, 129, 200 ...
Of course, when you do a tsquery search with "simple" configuration it
checks doesn't do any stemming so is actually looking for a lexeme
called "database" which it can't find.

Since it can't find anything, it falls back to displaying just the start
of the document. Since the alternative would be to display nothing, that
makes a certain amount of sense.

To check this, try: ts_headline(t, to_tsquery('simple','databas')) and
you should get your database results.

Moral of the story: if you specify a configuration, always specify it.

Thanks for working through this Stephen - good question specification btw.

--
Richard Huxton
Archonet Ltd

Not quite:-(

It is the ts_headline with the explicit "english" configuration that "fails"
rather than the implicit "simple".

That's what is so weird.

As you say, the ts_vector has "databas" so the "english" version of
ts_headline should work - but it doesn't. The "simple" version does; despite
the above.

Weird!

Stephen

On Friday 22 February 2008 19:33, Richard Huxton wrote:

Stephen Davies wrote:

OK. The first level explanation is that my default config is "simple".

Aha! Actually, that's the whole explanation.

This explains the different query results as "english" reduces "database"
to "databas" while "simple does not reduce it at all.

Exactly.

The "document" is parsed/indexed using "english" explicitly so my queries
nedd to be explicit also (not an issue as all "real" queries are
generated rather than typed).

Or change your default configuration to match the one you're using.

However, I still cannot see a reason for the ts_headline results. If
anything, they should be the other way around.

I suspect that ts_headline may only work properly when no configuration
is specified - regardless of the default setting.

No. What's happening is that your tsvector representation of the
document (which gets indexed) contains lexemes processed by your
"english" config. So, it will have something like:
... databas: 123, 129, 200 ...
Of course, when you do a tsquery search with "simple" configuration it
checks doesn't do any stemming so is actually looking for a lexeme
called "database" which it can't find.

Since it can't find anything, it falls back to displaying just the start
of the document. Since the alternative would be to display nothing, that
makes a certain amount of sense.

To check this, try: ts_headline(t, to_tsquery('simple','databas')) and
you should get your database results.

Moral of the story: if you specify a configuration, always specify it.

Thanks for working through this Stephen - good question specification btw.

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Stephen Davies wrote:

Not quite:-(

It is the ts_headline with the explicit "english" configuration that "fails"
rather than the implicit "simple".

Hmm... arse.

That's what is so weird.

As you say, the ts_vector has "databas" so the "english" version of
ts_headline should work - but it doesn't. The "simple" version does; despite
the above.

[goes away, tests some more]

OK, so:

set default_text_search_config = 'simple';
SELECT ts_headline('my database is a database', to_tsquery('database'));
SELECT ts_headline('my database is a database', to_tsquery('simple',
'database'));
SELECT ts_headline('my database is a database', to_tsquery('english',
'database'));

The first two work, the last one doesn't.

set default_text_search_config = 'english';
SELECT ts_headline('my database is a database', to_tsquery('database'));
SELECT ts_headline('my database is a database', to_tsquery('simple',
'database'));
SELECT ts_headline('my database is a database', to_tsquery('english',
'database'));

The middle one doesn't work.

Note that there are no indexes involved here, we're just running against
the raw text.

[light goes on over sluggish London-based database chap]

When the ts_headline function is working on the text, it needs to
convert it from varchar/text type to tsvector so that it can use the
tsquery to find words to highlight.

When it converts the text to a tsvector, it's doing it based on
default_text_search_config - we've not told it otherwise. In an ideal
world, it would look "inside" the tsquery and see what config that was
using, but it can't (or at least doesn't).

Of course, if to_tsquery()'s config doesn't match to_tsheadline()'s then
we get a problem.

And, if I actually bother to read an up-to-date copy of the manual,
rather than the beta version I've got linked on my desktop I can see
there's a parameter for ts_headline. So...

set default_text_search_config = 'simple';
SELECT ts_headline('english', 'my database is a database',
to_tsquery('english','database')
);

set default_text_search_config = 'english';
SELECT ts_headline('simple', 'my database is a database',
to_tsquery('simple','database')
);

These all work fine. Phew!

--
Richard Huxton
Archonet Ltd

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.

It begs the question, however, as to why ts-headline needs to reparse the raw
text.

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.

Cheers and thanks,
Stephen

On Friday 22 February 2008 20:00, Richard Huxton wrote:

Stephen Davies wrote:

Not quite:-(

It is the ts_headline with the explicit "english" configuration that
"fails" rather than the implicit "simple".

Hmm... arse.

That's what is so weird.

As you say, the ts_vector has "databas" so the "english" version of
ts_headline should work - but it doesn't. The "simple" version does;
despite the above.

[goes away, tests some more]

OK, so:

set default_text_search_config = 'simple';
SELECT ts_headline('my database is a database', to_tsquery('database'));
SELECT ts_headline('my database is a database', to_tsquery('simple',
'database'));
SELECT ts_headline('my database is a database', to_tsquery('english',
'database'));

The first two work, the last one doesn't.

set default_text_search_config = 'english';
SELECT ts_headline('my database is a database', to_tsquery('database'));
SELECT ts_headline('my database is a database', to_tsquery('simple',
'database'));
SELECT ts_headline('my database is a database', to_tsquery('english',
'database'));

The middle one doesn't work.

Note that there are no indexes involved here, we're just running against
the raw text.

[light goes on over sluggish London-based database chap]

When the ts_headline function is working on the text, it needs to
convert it from varchar/text type to tsvector so that it can use the
tsquery to find words to highlight.

When it converts the text to a tsvector, it's doing it based on
default_text_search_config - we've not told it otherwise. In an ideal
world, it would look "inside" the tsquery and see what config that was
using, but it can't (or at least doesn't).

Of course, if to_tsquery()'s config doesn't match to_tsheadline()'s then
we get a problem.

And, if I actually bother to read an up-to-date copy of the manual,
rather than the beta version I've got linked on my desktop I can see
there's a parameter for ts_headline. So...

set default_text_search_config = 'simple';
SELECT ts_headline('english', 'my database is a database',
to_tsquery('english','database')
);

set default_text_search_config = 'english';
SELECT ts_headline('simple', 'my database is a database',
to_tsquery('simple','database')
);

These all work fine. Phew!

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the sender and the person(s). No one else is authorised to use or
disseminate this email or its contents.

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Adelaide, South Australia. Fax: 08-8177 0133
Computing & Network solutions. Mobile:0403 0405 83

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.

--
Richard Huxton
Archonet Ltd

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.

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.

--
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This email is for the person(s) identified above, and is confidential to
the sender and the person(s). No one else is authorised to use or
disseminate this email or its contents.

Stephen Davies Consulting Voice: 08-8177 1595
Adelaide, South Australia. Fax: 08-8177 0133
Computing & Network solutions. Mobile:0403 0405 83

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@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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.

Would it be possible for ts_headline to work with the pre-parsed ts_vector?

I see references to future plans for phrase searching in ts. Is there a date
for this?

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@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83

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disseminate this email or its contents.

Stephen Davies Consulting Voice: 08-8177 1595
Adelaide, South Australia. Fax: 08-8177 0133
Computing & Network solutions. Mobile:0403 0405 83

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@sai.msu.su, 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@sai.msu.su, http://www.sai.msu.su/~megera/
phone: +007(495)939-16-83, +007(495)939-23-83