title: NLTK fcfg grammar using python
body: <p>I am new in NLP. I found this file in nltk_data.
  I am trying to write my own grammar. Before write these I need to know what is the meaning of (SEM=(?v + ?pp)).
  please help me to know this.</p>
  
  <pre><code>% start S
  
  S[SEM=(?np + WHERE + ?vp)] -&gt; NP[SEM=?np] VP[SEM=?vp]
  
  VP[SEM=(?v + ?pp)] -&gt; IV[SEM=?v] PP[SEM=?pp]
  VP[SEM=(?v + ?ap)] -&gt; IV[SEM=?v] AP[SEM=?ap]
  NP[SEM=(?det + ?n)] -&gt; Det[SEM=?det] N[SEM=?n]
  PP[SEM=(?p + ?np)] -&gt; P[SEM=?p] NP[SEM=?np]
  AP[SEM=?pp] -&gt; A[SEM=?a] PP[SEM=?pp]
  
  NP[SEM='Country="greece"'] -&gt; 'Greece'
  NP[SEM='Country="china"'] -&gt; 'China'
  
  Det[SEM='SELECT'] -&gt; 'Which' | 'What'
  
  N[SEM='City FROM city_table'] -&gt; 'cities'
  
  IV[SEM=''] -&gt; 'are'
  A[SEM=''] -&gt; 'located'
  P[SEM=''] -&gt; 'in'
  </code></pre>