5.4.4 Role Constraints

For each role \rho\in\setof{Roles} there is a corresponding binary predicate \Gamma_\rho. The third principle of well-formedness requires that whenever the dependency tree contains an edge w\EDGE\rho w', then the grammatical condition \Gamma_\rho(w,w') must hold in the tree. Therefore the tree must satisfy the proposition below:

\forall w,w'\in\VV,\ \forall\rho\in\setof{Roles},\quad
w'\in\rho(w)\Rightarrow\Gamma_\rho(w,w')

In practice, the proposition will be enforced by creating a disjunctive propagator for each triple (w,w',\rho):

w'\in\rho(w)\wedge\Gamma_\rho(w,w')\quad\textbf{or}\quad
w'\not\in\rho(w)

For illustration, let's consider some examples of \Gamma_\rho(w,w').

Subject.

The subject of a finite verb must be either a noun or a pronoun, it must agree with the verb, and must have nominative case. We write \SET{nom} for the set of agreement tuples with nominative case:

\Gamma_{\Feature{subject}}(w,w')\equiv
\begin{array}[t]{ll}
&\Feature{cat}(w')\in\{\Value{n},\Value{pro}\}\\
\wedge&\Feature{agr}(w)=\Feature{agr}(w')\\
\wedge&\Feature{agr}(w')\in\SET{nom}
\end{array}

Adjective.

An adjective may modify a noun and must agree with it:

\Gamma_{\Feature{adj}}(w,w')\equiv
\begin{array}[t]{ll}
&\Feature{cat}(w)=\Value{n}\\
\wedge&\Feature{cat}(w')=\Value{adj}\\
\wedge&\Feature{agr}(w)=\Feature{agr}(w')
\end{array}


Denys Duchier
Version 1.2.0 (20010221)