Head-driven Phrase Structure Grammar I

Basic Idea Typed feature structure HPSG: First glance
TFS subsumption: Formal definition
◮ π ≡ F π ′ : feature structure F contains path equivalence or
reentrancy between the paths π and π ′
Definition
◮ δ(r, π) = δ(r, π ′ ) where r is the root node of F.
F subsumes F ′ , written F ⊑ F ′ , if and only if:
◮ π ≡ F π ′ implies π ≡ F ′ π ′
◮ θ(δ(r, π)) = σ implies θ(δ(r ′ , π)) = σ ′ and σ ⊑ σ ′ .
In other words, feature structure F subsumes feature structure F ′
(F ⊑ F ′ ) iff:
1. if path π is defined in F then π is also defined in F ′ and the
type of the value of π in F is a supertype or equal to the type
of the value of π in F ′ , and
2. all paths that are reentrant in F are also reentrant in F ′ .
Weiwei Sun Head-driven Phrase Structure Grammar I 32/61