= Automatic Semantic Tool (AST) =
Full semantic analysis of natural language (NL) texts is an open
problem. The most comprehensive semantic systems build upon a mathematically
sound formalism of a selected logical system. Mostly due to computability
and efficiency, current systems work with the first order logic (or its variant).
However, the low-order logic is not appropriate for capturing higher-order
phenomena that occurs in natural language, such as belief attitudes, direct
speech, or verb tenses. In our project, we develop new tool for automatic semantic analysis
(AST) that emerged from (a module of) the Czech syntactic parser [https://nlp.fi.muni.cz/trac/synt SYNT] .
AST is now a standalone tool based on Transparent Intensional Logic (TIL).
It works with the same input files (lexicons, semantic rules, ...) that were designed and developed in SYNT.
AST can provide a semantic analysis in the form of Transparent Intensional Logic (TIL) constructions independently on the input syntactic parser and language.
Adaptation for new language consists in a specification of four lexicon files that describe lexical items, verb valencies, prepositional valencies and a semantic grammar.
== Input ==
To create a semantic structure of a sentence, AST needs the output from
previous analysis. A usual output is in the form of a syntactic tree.
'''Textual form of syntactic tree:'''
{{{
{##start##
{start
{ss
{clause
{VL0Jedl
jístk5eAaIgMnS}
{intr
{adjp
{ADJ1pečené
pečenýk2eAgNnSc4}
}
{np
{N2kuře
kuřek1gNnSc4}
}
}
}
}
{ends
{'.'3..kX }
}
}
}
}}}
'''Corresponding graphical representation:'''
[[Image(tree.png, 700px)]]
Besides the tree nodes and edges, the tree contains morphological information about each word: a lemma and a PoS tag, which are used by AST for
deriving implicit out-of-vocabulary type information
== Language Dependent Files ==
The core of AST system is universal and can be used for semantic analysis of any
language. Besides main core the system also uses input files that are language
dependent and that need to be modified for new language.
'''The Semantic Grammar''': resulting semantic construction is built by
bottom-up analysis based on the input syntactic tree provided by the syntactic
parser and by a semantic extension of the actual grammar used in the parsing
process. To know which rule was used by the parser, AST needs the semantic
grammar file. This file contains specification of semantic actions that need
to be done before propagation of particular node constructions to the higher
level in the syntactic tree. The semantic actions define what logical functions
correspond to each particular syntactic rule. For instance, the node in
graphical representation corresponds to the rule and action:
{{{
np -> left_modif np
rule_schema ( "[#1,#2]" )
}}}
which says that the resulting logical construction of the left-hand side np is
obtained as a (logical) application of the left_modif (sub)construction to the
right-hand side np (sub)construction. Example of building construction from two subconstructions is presnet in following example:
[[Image(analysis.pdf, 700px)]]