Eckhard Bick - VISL

all - 356 978 492 2219
C-percent 39.0 35.9 10.2 29.1
However, though the relative distribution remains similar to that of absolute contexts,
the proportion of safe conditions (the C-percent parameter) is consistently lower for
unbounded contexts. Unbounded contexts are usually defined in a more restrictive way
than absolute contexts that only check for one particular tag set. In contrast, as
mentioned above, most unbounded contexts have BARRIER or LINK (often even LINK
0) conditions attached that further restrict instantiation of the context. BARRIER
conditions are unbounded backwards-looking NOT conditions 123 and are thus part of
the safe context group, and many LINK contexts are themselves specified as C. With
such a wealth of linked information, the chance of error when instantiating an
unbounded context is thus smaller than for ordinary, absolute contexts, and the parser's
philosophy is: Rather find an ambiguous word context that matches all the additional,
relative context specifications than not use it just because it happens to have another
local reading not itself sustained by further relative context.
The leftward leaning tendency for unbounded contexts is about the same as for
absolute contexts, about 60%.
(6) Proportion of leftward context conditions (% left/all contexts)
morf0 syn0 map all
absolute contexts 60.6 60.5 66.7 61.3
unbounded contexts 56.6 63.0 64.6 62.4
Interestingly, this is not what Anttila finds for the English CG. In (Karlsson et. al.,
1995, p. 352) he cites 81% for unbounded and 42.6% 124 for absolute contexts,
supposedly for the syntactic segment of the English grammar. As an explanation for the
high figure for unbounded contexts, Anttila refers to the fact that such rules are about
phrase structure generalisations and that, in English, heads usually precede their
complements. In the same vein one can argue that Portuguese here displays a lower
figure, because its word order is not as strictly regulated as that of English.
Still, for absolute contexts, the Portuguese figure is higher than the corresponding
English one, and not significantly different from that for unbounded contexts in the
Portuguese CG. An explanation may be that the English rules concerned were meant as
small window rules akin to heuristic rules (as suggested ibd., p. 353), whereas the
123 the BARRIER condition was not present in the cg1-compiler. There, it would have to be expressed as a hooked (now:
LINKed) unbounded context condition in the opposite direction. But even then, barrier function was intended - unbounded
context searches would not be allowed to cross the zero position.
124 My computation, - the article cites absolute figures, not percentages, for the absolute contexts.
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