Towards LFG

[kawu]

Features

To describe LFG grammars with our formalism the following features would be needed:

• Representing sets with feature structures.
• "We require the f-structure solution for a particular f-description to be the minimal solution to the f-description" <- does it have any implications for the unification process?
• Distinction between defining and constraining equations. In particular, it seems that implementing constraining equations would require extending the current unification mechanism.
• Other types of defining/constraining equations: negative equation, existential constraint, etc.
• Boolean expressions over (defining/constraining) equations.
• Regular expressions (there's an example with the Kleene star in [1], page 17) over paths in equations. The so-called functional uncertainty.
• Inside-out function application.
• Off-path constraints.

See also http://www2.parc.com/isl/groups/nltt/xle/doc/notations.html.

Off-path constraints

Hyphothesis: off-path constraints provide means to describe tree-structured constraints. Question 1: is it possible to describe graph-structured constraints? Question 2: is it possible to describe tree-structured constraints with several roots?

NOTE: the hyphothesis is not quite true, to represent a tree of constraints we can just use a set of path constraints. The problem is the semantics of regular and off-path constraints with respect to feature sets and quantification scope (at least, such an issue exists in LFG, it seems).

References

[1] Lexical Functional Grammar, Mary Dalrymple

[kawu]

Not really related to the library which implements feature structures of general form.