hi I'm new to phrase/dependency structure. For a project of mine I want to extract from any sentence a meaningful structure with 3 items i.e. triple.

In general case the Subject-Verb-Object is ideal. The problem is for many sentences some of the items from the triple is missing.

My question is what other element/s of POS/DEP is suitable to fill in, so I can always have triple (except in the case of 2 word sentences :))

What about sentences which do not have a VERB ? Is there are part of Linguistics that research those ? Links ? Can I still generate triplets based on some other structural information ?

1 Answer 1


You could use DOOM, which in a cfg is a non-terminal symbol that does not occur on the left-hand side of any phrase structure rule. Since a cfg does not generate any string containing a non-terminal symbol, once DOOM gets into a phrase structure derivation, it poisons the derivation, which can never lead to generating a grammatical sentence. (A DOOM marking convention was suggested by Paul Postal.)

  • 1
    what is DOOM, can you provide a link
    – sten
    Commented Aug 6, 2019 at 23:53
  • I said what it is: a non-terminal symbol of a cfg which occurs on the right side of some phrase structure rule, but never occurs as the left hand side of a phrase structure rule. How could I be more explicit? No, I can't provide a link. Link to me.
    – Greg Lee
    Commented Aug 7, 2019 at 21:09
  • ooo cfg = context free grammar ..... i see, will look it up
    – sten
    Commented Aug 7, 2019 at 21:24

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