Multi-term phrases in Lucene

Question

I am reading the Lucene in Action book and I do not understand the multi-term phrases part.

The following text is indexed:

the quick brown fox jumped over the lazy dog

And then you add the following terms to the PhraseQuery : quick jumped lazy with a slop equal 4. That results in a match, but I don't understand how that happens. How do you calculate the number of moves when there are multiple terms? I don't understand how they do it.

The same with the terms lazy jumped quick with slop equal 8.

Answer 1

The slop is actually an edit distance . Inserting extra terms in between them adds 1 to the distance, transposing terms adds 2 (the first edit moving the two terms atop one another).

You can go through the edits one at a time to illustrate:

• quick jumped lazy distance:0
• quick _ jumped lazy distance:1
• quick _ _ jumped lazy distance:2
• quick _ _ jumped _ lazy distance:3
• quick _ _ jumped _ _ lazy distance:4

And for the second case:

• lazy jumped quick distance:0
• lazy/jumped quick distance:1
• lazy/jumped/quick distance:2 (all three terms superimposed, in the same position)
• quick lazy/jumped distance:3
• quick jumped lazy distance:4
• quick _ jumped lazy distance:5
• quick _ _ jumped lazy distance:6
• quick _ _ jumped _ lazy distance:7
• quick _ _ jumped _ _ lazy distance:8