Linguistics 581

Context-Free grammars

Homework assignment

Grammars

A. End of chapter 11. Exercises 11.1, 11.2.


For exercises 11.1 and 11.2 you should start with the ATIS Grammar, which is given in slightly fuller form in Chapter 12, in Figure 12.1.

You will need to make some changes to the grammar in Fig. 12.1 to handle everything in 11.1 and 11.2, especially 11.2:

  1. First, you will need to add some words to the grammar.
  2. Then you will need to adds some rules.
Keep track of the additions you have to make to the grammar to draw adequate trees for the phrases and sentences in 12.1 and 12.2. You will hand those in as hard copies as part of the assignment.

B. Part 1. Next consider the next two sentences:

    (a) I would like a flight to the capital from Boston
    (b) I would like a steak with a side of fries
      Pronoun Aux Verb Det Noun Preposition Det Noun Preposition Noun
                  D N1 P N2
These two sentences have exactly the same parts of speech but they do not have the same syntactic analysis (trees). In (b), the Det Noun Preposition Noun sequence a side of fries is an NP. (For ease of reference in the discussion below, we've labeled the parts of the last for words D N1 P N2).

In (a), the corresponding words the capital from Boston is not an NP. Think about this for a moment. You could not make the capital from Boston the subject of a sentence. The reason that from Boston is there is that it's telling us where the flight is from (not where Boston is from). We capture this semantic fact by drawing a syntactic tree in which the noun flight is modified by two PPs ( to the capital and from Boston) which spell out the itinerary of the flight. In that tree the capital from Boston is not an NP. In fact it's not even a phrase. The difference between the (a) and (b) sentences is called a structural difference. See if you can draw the right trees to capture this structural. There are various choices you can make, but see if you can draw trees that make both a flight to the capital from Boston and a steak with a side of fries NPs. You will certainly have to add words to the grammar. You may have to add other kinds of rules to the grammar. Do you?

Draw the correct trees representing the structural difference by hand. Report any changes you had to make to the grammmar to get the right trees.

The following phrases all have the same parts of speech as steak with side of fries and flight from capital to Boston. In each case, decide whether the tree should look like the tree for steak with side of fries (N2 P2 N3 is an NP) or like flight from capital to Boston (N2 P2 N3 is not an NP).

  1. file with letter to governor
  2. picture of wife on desk
  3. reminder of obligation to family
  4. removal of demonstrator from premises