A5: Syntax

Author: Nathan Schneider

This is a pen-and-paper assignment to give you practice with constituency syntax and parsing. (Dependency syntax/parsing is not covered in this assignment due to the timing of deadlines, but it will be on the exam!)

The breakdown into 60 points is shown. Warning: Allow plenty of time for the last 2 parts!

Questions will concern the sentence:

What will you purchase me for my birthday in July?

You may find it useful to consult the textbook's description of syntactic analysis of English (ignore the part about traces and movement). We recommend that you watch the following video to familiarize yourself with the concepts required for the upcoming questions. Lexical and syntactic ambiguity

  1. [1 pt] What is the sentence type: declarative, imperative, interrogative, or interjection?
  2. [2 pts] Identify two words in the sentence that are ambiguous with respect to part-of-speech (POS). Explain.
  3. [2 pts] Assuming the contextually correct POS tags, identify a structural ambiguity in the sentence.
  4. [5 pts] Assign the contextually correct POS to words (ignoring punctuation) from the following list:
  1. [15 pts] For each structurally ambiguous reading, draw a constituency (phrase structure) tree. Include parts of speech as preterminal categories. Use the following phrasal categories (ignore punctuation):

Hint 1: Neither the subject nor anything before it should be in a VP.
Hint 2: Apart from the terminals, there should be 4 unary branching structures.

  1. [10 pts] Give a small context-free grammar that allows the two constituency trees. You do not have to write out rules for the lexicon entries.
    Hint: My solution has 9 rules.
  2. [1 pt] Assuming a finite lexicon, does your CFG describe a finite or infinite string language?
  3. [4 pt] Give two examples where your CFG overgenerates, i.e., allows a sentence that is not really grammatical English.
  4. [5 pts] Binarize the grammar so it is in Chomsky-Normal Form (CNF).
    Hint: There are multiple valid ways to do this. My solution has 23 binary rules, which contain only nonterminals (phrasal categories and POS tags) on the RHS.
  5. [15 pts] Use the CNF CFG to fill out the CKY chart for constituency parsing the sentence. A template is provided. Assume the correct POS tags are already determined. (Ignore punctuation.) Ensure both valid parses are encoded in the chart. There should also be some possible constituents that do not lead to a full parse.