  This paper deals with the exploitation of dictionaries for the semi-automatic
construction of lexicons and lexical knowledge bases. The final goal of our
research is to enrich the Basque Lexical Database with semantic information
such as senses, definitions, semantic relations, etc., extracted from a Basque
monolingual dictionary. The work here presented focuses on the extraction of
the semantic relations that best characterise the headword, that is, those of
synonymy, antonymy, hypernymy, and other relations marked by specific relators
and derivation. All nominal, verbal and adjectival entries were treated. Basque
uses morphological inflection to mark case, and therefore semantic relations
have to be inferred from suffixes rather than from prepositions. Our approach
combines a morphological analyser and surface syntax parsing (based on
Constraint Grammar), and has proven very successful for highly inflected
languages such as Basque. Both the effort to write the rules and the actual
processing time of the dictionary have been very low. At present we have
extracted 42,533 relations, leaving only 2,943 (9%) definitions without any
extracted relation. The error rate is extremely low, as only 2.2% of the
extracted relations are wrong.
