Constituency and Dependency Parsing › Worked Example: Two Readings of One Sentence

Return to "the man saw the dog with a telescope". Ignore morphological details and use simplified labels.

Reading A attaches the prepositional phrase to the verb phrase. The man used a telescope to see the dog.

S
├── NP: the man
└── VP
    ├── VP
    │   ├── V: saw
    │   └── NP: the dog
    └── PP: with a telescope

Reading B attaches the prepositional phrase to the noun phrase "the dog". The dog had a telescope.

S
├── NP: the man
└── VP
    ├── V: saw
    └── NP
        ├── NP: the dog
        └── PP: with a telescope

In dependency form, the difference is one arc. Reading A makes "telescope" a dependent of "saw" through an oblique relation. Reading B makes "telescope" a dependent of "dog" through a nominal modifier relation. The rest of the tree can stay the same. This illustrates how much meaning can hinge on a single structural decision: the two trees differ in exactly one attachment, yet they describe different situations in the world.

The same words and part-of-speech tags permit different attachments. A scoring model ranks these relations using its available input. Surrounding discourse can favor one reading; a sentence-only input may leave that intended distinction unresolved even when the model assigns different scores to the two trees.