Grammar Writing: Week 10
Identity
Last week, you were supposed to write a grammar that accepts different kinds of verb phrases. The rules you had to write all took the following form:
1. VP --> V, COMPS <NP> + NP
2. VP --> V, COMPS <PP> + PP
3. VP --> V, COMPS <AP> + AP
4. VP --> V, COMPS <sentence> + sentence
For NPs, APs, PPs you would also have to write several rules.
Clearly, the rules above are very similar, but they fail to express the similarity. This is shown by the fact that if there were a verb that wants to combine with a VP-complement, then we would would need to add another rule to the ones above, as follows:
5. VP --> V, COMPS <VP> + VP
What our current grammars are missing to express the generalization covered by the five rules above is the concept of feature structure identity. By identity, we mean that one larger feature structure contains a smaller feature structure twice, in different places. Or more simply, that the information at two places in a feature structure must be the same.
In order to signal such identity, we will use so-called boxed numbers, i.e. 1,2,3, ... with a box around it. Unfortunately, in this WIKI, we cannot represent such boxes. Therefore, we will use symbols like the following as identity markers: ©1, ©2, ©3, ...
With the concept of feature structure identity and the notation above, we can now replace the 5 rules above by the one single rule below:
6. VP --> V, COMPS <©1> + ©1
The effect of rule 6. can be stated informally as follows:
A verb phrase can be formed from a V that is looking for a ©1 as its complement and one ©1.
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