Eckhard Bick - VISL

example is a grammar of one terminal and the rule (x) -> ((x)) which produces an
infinite language of “sentences” with paired brackets. One of the very few examples
from the domain of natural language is Swiss German that has a construction where
word order in two verbal sections of a sentence is cross-dependent. But since even such
examples can be circumvented for constructions of finite depth, by writing as many
context free rules to cover the phenomenon [for the bracketing example, (x) -> ((x)),
((x)) -> (((x))), (((x))) -> ((((x)))), ...], most generative parsers have been built around
context free grammars.
In most languages, morphological structure is more linear than syntactic structure, and
therefore easier to describe in an FSM framework. Thus, the TWOL-systems
(Koskenniemi, 1983) used to supply analyser-input for most Constraint Grammars,
describe words as linear morpheme transitions, allowing for phonetically motivated
surface level changes at morpheme borders. Thus, the word ‘unrecognisable’ would be
analysed as ‘un_recognis(e)_able’. Here, the FSM contains transition paths from
preverbal prefix to verbal root, and from verbal root to postverbal suffix, expressed as
so-called alternation of sub-lexica. A surface-level rule removes the ‘e’ of ‘recognise’
because of the clash with the ‘a’ of ‘-able’. All inflexion and most cases of derivation
and compounding can be handled this way 96 .
On a syntactic level, on the other hand, it is very hard to imagine a FSM capable of
describing free natural language, though the technique has been explored in recent years
by, for instance, Atro Voutilainen (1994:32ff).
The generative grammars of the context free type used for syntactic parsing, try to
achieve several objectives at the same time: They analyse sentences by generating
sentences, and they disambiguate both word class and function by assigning structure.
While this does not by itself pose unresolvable technical problems, the conceptual
priorities of generative grammar do seem to make it less efficient in a parsing context,
i.e. for identifying “partes orationis”, or “parts-of-speech” on a morphological and
functional level:
• 1. In generative grammar, there is a tradition of assigning low priority to broad
lexicography, which can be explained by the fact that “toy lexica” are fine for
generating sentences, while being unsatisfactory for research on parsing [free]
sentences.
• 2. The constituent structure approach creates its own, theory-specific ambiguity
priorities, some of which, like the scope of postnominal attachment or some cases of
96 One might, of course, argue, that ‘un-’ as a preverbal prefix is limited to transitivized denominal verbs, usually ending in
‘-ize’/’-ise’ or ‘-ate’. For productive word composition one would then need a higher level (context free) rule to describe the
interdependence of the causative suffix and the antonymous prefix.
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