  Recently researchers working in the LFG framework have proposed algorithms
for taking advantage of the implicit context-free components of a unification
grammar [Maxwell 96]. This paper clarifies the mathematical foundations of
these techniques, provides a uniform framework in which they can be formally
studied and eliminates the need for special purpose runtime data-structures
recording ambiguity. The paper posits the identity: Ambiguous Feature
Structures = Grammars, which states that (finitely) ambiguous representations
are best seen as unification grammars of a certain type, here called
``interaction-free'' grammars, which generate in a backtrack-free way each of
the feature structures subsumed by the ambiguous representation. This work
extends a line of research [Billot and Lang 89, Lang 94] which stresses the
connection between charts and grammars: a chart can be seen as a specialization
of the reference grammar for a given input string. We show how this
specialization grammar can be transformed into an interaction-free form which
has the same practicality as a listing of the individual solutions, but is
produced in less time and space.
