Phrase structure rules can be extended with LFG functional notations. The functional notation(s) of a symbol must be entered inside curly brackets.
S → NP { (↑ SUBJ) = ↓; } VP { ↑ = ↓; };
The parser can handle the following notation types
- defining equation
- constraining equation
- negative equation
- existential constraint
- negative existential constraint
Defining equations
A defining equation is an equation that contains the equal sign (=) or the element of (∈)
equality equation
In a functional notation, the equal sign (=) will unify the left and the right member. The value of both members will be replaced with the result of the unification.
S → NP
{
↑ = ↓;
}
Unification of the functional structure of the constituent NP (down arrow) with the functional structure of the constituent S (up arrow)
membership equation
The element of (∈) can be used to add the functional structure of the left constituent in a set (the right member)
NP → DET {↑=↓;} (ADJ)* { ↓ ∈ (↑MOD);} N {↑=↓;};
Add the functional structure of every adjective to a set. The set is the value of the attribute MOD of the constituent NP (and also of the constituents DET, N because of the equality equation)