While there is conclusive proof that not all natural languages can be
described by context-free grammars, all available evidence suggests that
a very cautious extension of this complexity class is sufficient to
accommodate all linguistic phenomena. Research on this issue has led to
the notion of "mild context-sensitivity". A range of
corresponding formalisms is well-established (e.g. Tree Adjoining
Grammars, Linear Indexed Grammars, Combinatory Categorial Grammars,
Head Grammars, and also Stabler's Minimalist Grammars).
The first part of the course aims to recapitulate the motivations for
employing non-context-free devices in formal linguistics. We will show
that certain stronger-than-context-free means are not only more
appropriate for reasons of weak generative power, but also permit
theoretically more elegant and satisfactory structural descriptions (e.g.
pertaining to non-local dependencies).
In the second part of the course, the most common mildly
context-sensitive devices - Tree Adjoining Grammars and Combinatory
Categorial Grammars - will be introduced formally, and their usefulness
for working linguists as well as their applications in language
technology methods will be demonstrated.
Finally we will briefly outline how most of the MCSG-formalisms become
comparable in terms of "linear context-free rewriting systems".