Análisis sintáctico conducido por un diccionario de patrones de ...

semantic network to give a measure of “semantic nearness” between constituents. For
this purpose we assign different weights to relations, hierarchy concepts links and
implicit relations.
In our model the advanced government patterns dictionary is the most
practical to solve most of the structure ambiguities. The dictionary reflects the
properties of the language itself, giving the syntactic constructions for each
predicative word, i.e. the entire subcategorization information for each specific word.
For Spanish, there are no dictionaries with complete subcategorization information.
There is some spread information considered by several authors. For a big dictionary
we require thousands of entries but manual work implies labor intensive and so much
time. We propose a statistical method to compile the syntactic information.
We propose a method to compile the frequency of combinations. These
combinations correspond to the specific predicative words and the prepositions that
introduce their valences. In our dictionary, the weight of a combination is defined as
the quotient of the frequency of the combination in the correct variants of parsing, i.e.,
in the texts, and its frequency in the incorrect variants of syntactic structures produced
by the specific analyzer.
The statistical model to obtain those frequencies is based on two sources: one
generating the true structures and one generating noisy variants which represent the
parser’s mistakes. Thus, some combinations can have a weight greater than 1, which
means that this combination appears in correct variants more frequently than in
incorrect ones. Others can have a weight inferior to 1, which means that they more
frequently appear in false variants. Finally, some combinations may have a weight of
1, which means that this combination is useless for disambiguation, even if it is
frequent in the texts.
The statistical weights give actually the possibility to change the whole point
of view on the nature and use of the dictionary that is used for the purpose of
disambiguation, giving the kinds of errors that an analyzer makes. We obtained those
weights by an iterative process. The process begins with an empty dictionary. For
each phrase all hypothesis about syntactic structure made by the parser have the same
weights in the first iteration. Once the frequency of the combination in the correct
variants in the texts and its frequency in the incorrect variants of syntactic structure
are determined for each founded combination a new weight calculation for all the
variants is made. These steps are repeated until the difference between weights
obtained in the previous iteration and the actual iteration is not greater than the
established threshold.
Since such a dictionary should contain statistical weights of the combinations
for specific words, we employ the method on the texts of the LEXESP Spanish
corpus. We test the obtained results of the syntactic information compiled for the
advanced government patterns dictionary on a group of 100 sentence extracted from
that corpus and parsed by the CFG module. The true structures for the input sentences
probed to be classified in the 35% rank of our experiments.
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