Functional notations

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)