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 L02 CFG: Phrase struc trees to meaning


    PHRASE STRUCTURE TREE to MEANING

o Relating a phrase structure tree to a modifier-modified tree

o Example sentence 1:  'arrow of son of Dasarath'
   * Phrase structure tree 1:

              NP_1
               |                  
       .--------------.
       |    |         |
       n   of        NP_2
       |              |
       |        .----------.
     arrow      |   |      |
                n  of     NP_3
                |          |
               son     n-proper
                           |
                       Dasarath

o Notion of the head of a phrase
  - What is the head of NP_1 ?
  + Consider Ex. The arrow of son of Dasarath is sharp
    - Who/what is sharp: arrow, son, Dasarath?
      . Ans: Arrow. Therefore, 'arrow' is the head of NP_1
  + Consider Ex. The son of Dasarath is sincere.
    - Who is sincere: Son, Dasarath?
      . Ans: Son. Therefore, 'son' is the head of NP_2

  * Head of a phrase is determined by rules of the language:
    - In case of NPs with 'of' in English, the noun on 
      the left is the head.

o Modifier-modified tree 1 (for the example on the top):

       arrow
         |
         |of
         |
        son
         |
         |of
         |
      Dasarath
         
o Example sentence 2: 'Ram saw Mohan'
   * Phrase structure tree:

               S
               |
         .----------.
         |          |
        NP         VP
         |          |
         |      .------.
     n-proper   |      |
         |      v     NP
        Ram     |      |
               saw   n-proper
                       |
                      Ram

   * Modifier-modified tree:

        saw
         |
      .-----.
      |k1   |k2
      |     |
     Ram  Mohan

o Rules can be prepared for converting from ps-tree to mm-tree
  (later)
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