title: What are the "-P"s in the Berkeley Aligner's output format?
body: <p>I want to use the Berkeley Aligner for some MT research I'm doing, since, apparently, it beats GIZA++ pretty handily (a 32% alignment error reduction in some reported results).  For the most part the outputs in the Berkeley Aligner "examples" directory look like what Moses does to GIZA++ output files (i.e., paired aligned word indices), but there are some funny looking "-P"s after certain pairs.  I can't for the life of me find any documentation  of what these "-P" annotations are supposed to signify (certainly not in the Berkeley Aligner "documentation" directory).</p>
  
  <p>For clarity, I'll give a little illustrative example.  Suppose you have the sentences: "Jean plâit à Marie" and "Marie likes Jean".  French is the source language and English is the target language. The words "Jean" (indices 0 and 2, resp.) and "Marie" (indices 3 and 0, resp.) are aligned in both sentences, and "plâit" and "à " (French indices 1 and 2, resp.) are aligned with "like" (English index 1).  In Moses-post-processed GIZA++ output, this would be denoted by a list of source-target index pairs:</p>
  
  <pre><code>0-2 1-1 2-1 3-0
  </code></pre>
  
  <p>Berkeley Aligner produces files that pretty much resemble this, but some index pairs have a -P on them (e.g., you <em>might</em> see something like 1-1-P).</p>
  
  <p>What the heck does this mean? Can I safely remove these -P annotations and get a GIZA++-via-Moses style alignment, or should I be doing something more (e.g., multiplying them out into a series of aligned index pairs, or what have you)?</p>