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From "Hoss Man (JIRA)" <>
Subject [jira] Created: (LUCENE-1626) getPositionIncrementGap(String fieldname, int currentPos)
Date Fri, 01 May 2009 19:03:30 GMT
getPositionIncrementGap(String fieldname, int currentPos)

                 Key: LUCENE-1626
             Project: Lucene - Java
          Issue Type: New Feature
          Components: Search
    Affects Versions: 2.4
            Reporter: Paul Cowan
            Priority: Minor

This issue is to cover the changes required to do a search across multiple fields with the
same name in a fashion similar to a many-to-one database. Below is my post on java-dev on
the topic, which details the changes we need:


We have an interesting situation where we are effectively indexing two 'entities' in our system,
which share a one-to-many relationship (imagine 'User' and 'Delivery Address' for demonstration
purposes). At the moment, we index one Lucene Document per 'many' end, duplicating the 'one'
end data, like so:

    userid: 1
    userfirstname: fred
    addresscountry: au
    addressphone: 1234

    userid: 1
    userfirstname: fred
    addresscountry: nz
    addressphone: 5678

    userid: 2
    userfirstname: mary
    addresscountry: au
    addressphone: 5678

(note: 2 Documents indexed for user 1). This is somewhat annoying for us, because when we
search in Lucene the results we want back (conceptually) are at the 'user' level, so we have
to collapse the results by distinct user id, etc. etc (let alone that it blows out the size
of our index enormously). So why do we do it? It would make more sense to use multiple fields:
    userid: 1
    userfirstname: fred
    addresscountry: au
    addressphone: 1234
    addresscountry: nz
    addressphone: 5678

    userid: 2
    userfirstname: mary
    addresscountry: au
    addressphone: 5678

But imagine the search "+addresscountry:au +addressphone:5678". We'd like this to match ONLY
Mary, but of course it matches Fred also because he matches both those terms (just for different

There are two aspects to the approach we've (more or less) got working but I'd like to run
them past the group and see if they're worth trying to get them into Lucene proper (if so,
I'll create a JIRA issue for them)

1) Use a modified SpanNearQuery. If we assume that country + phone will always be one token,
we can rely on the fact that the positions of 'au' and '5678' in Fred's document will be different.

   SpanQuery q1 = new SpanTermQuery(new Term("addresscountry", "au"));
   SpanQuery q2 = new SpanTermQuery(new Term("addressphone", "5678"));
   SpanQuery snq = new SpanNearQuery(new SpanQuery[]{q1, q2}, 0, false);

the slop of 0 means that we'll only return those where the two terms are in the same position
in their respective fields. This works brilliantly, BUT requires a change to SpanNearQuery's
constructor (which checks that all the clauses are against the same field). Are people amenable
to perhaps adding another constructor to SNQ which doesn't do the check, or subclassing it
to do the same (give it a protected non-checking constructor for the subclass to call)?

2) It gets slightly more complicated in the case of variable-length terms. For example, imagine
if we had an 'address' field ('123 Smith St') which will result in (1 to n) tokens; slop 0
in a SpanNearQuery won't work here, of course. One thing we've toyed with is the idea of using
getPositionIncrementGap -- if we knew that 'address' would be, at most, 20 tokens, we might
use a position increment gap of 100, and make the slop factor 50; this works fine for the
simple case (yay!), but with a great many addresses-per-user starts to get more complicated,
as the gap counts from the last term (so the position sequence for a single value field might
be 0, 100, 200, but for the address field it might be 0, 1, 2, 3, 103, 104, 105, 106, 206,
207... so it's going to get out of sync). The simplest option here seems to be changing (or
   public int getPositionIncrementGap(String fieldname)
   public int getPositionIncrementGap(String fieldname, int currentPos)
so that we can override that to round up to the nearest 100 (or whatever) based on currentPos.
The default implementation could just delegate to getPositionIncrementGap().


Patches (x2) to follow shortly

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