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# Other Features

neg, possible values are +, -
Used for controlling the interaction of negation and auxiliary verbs. pred, possible values are +, -
The pred feature is used in the following tree families: Tnx0N1.trees and Tnx0nx1ARB.trees. In the Tnx0N1.trees family, the following equations are used:
for W1nx0N1:
(567)0(567
(568)
NP1.t:pred = +  (568)0(568
(569)
NP1.b:pred = +  (569)0(569
(570)
NP.t:pred = +  (570)0(570
(571)
N.t:pred = NP.b:pred

This is the only tree in this tree family to use the pred feature. The other tree family where the pred feature is used is Tnx0nx1ARB.trees. Within this family, this feature (and the following equations) are used only in the W1nx0nx1ARB tree.

(571)0(571
(572)
AdvP1.t:pred = +  (572)0(572
(573)
AdvP1.b:pred = +  (573)0(573
(574)
NP.t:pred = +  (574)0(574
(575)

pron, possible values are +, -
This feature indicates whether a particular NP is a pronoun or not. Certain constructions which do not permit pronouns use this feature to block pronouns. tense, possible values are pres, past
It does not seem to be the case that the tense feature interacts with other features/syntactic processes. It comes from the lexicon with the verb and is transmitted up the tree in such a way that the root S node ends up with the tense feature of the highest verb in the tree. The equations used for this purpose are:

(575)0(575
(576)
Sr.b:tense = VP.t:tense  (576)0(576
(577)
VP.b:tense = V.t:tense

trans, possible values are +, -
Many but not all English verbs can anchor both transitive and intransitive trees.

(577)0(577
(578)
The sun melted the ice cream.  (578)0(578
(579)
The ice cream melted.  (579)0(579
(580)
Elmo borrowed a book.  (580)0(580
(581)
* A book borrowed.

Transitive trees have the trans feature of their anchor set to + and intransitive trees have the trans feature of their anchor set to -. Verbs such as melt which can occur in both transitive and intransitive trees come unspecified for the trans feature from the lexicon. Verbs which can only occur in transitive trees e.g. borrow have their trans feature specified in the lexicon as + thus blocking their anchoring of an intransitive tree.

Next: Evaluation and Results Up: Features Previous: Control
XTAG Project
1998-09-14