Eckhard Bick - VISL

word order can't be counted on to make the distinction. To a lesser degree, secondary
semantic tags can help resolve morphological word stem ambiguities, too - e.g. where
two words share all graphical features (in some or all of their inflexional forms), and
only differ in pronunciation, or not at all. The Portuguese verbs ‘ser’ and ‘ir’, for
example, have a large overlap in inflexional forms. Thus, ignoring auxiliary functions,
‘foi’ can mean both ‘I/he was’ and ‘I/he went’. However, given the semantic subject
restrictions of a MOVE-verb like ‘ir’, ‘foi’ can be disambiguated as a copula (‘ser’) if
the subject is not .
Finally, a list of alternative (mutually exclusive) semantic tags attached to one
word can be exploited for sense distinction in polysemic lexical items, as desirable in,
for instance, machine translation or information extraction. To this end, the semantic
tags themselves need to be subjected to disambiguation. This can be achieved by
unifying semantic tags from syntactic arguments with semantic slots from their valency
head. Thus, speech verbs would have a semantic subject slot, that says +HUM, action
and activities would have a slot saying +ANIM. Thus, a singing star (+HUM) is not the
same kind of star as a falling star (-HUM).
Even before the introduction of semantic tags proper, semantic information has been
used in the CG-rules of my parser - by declaring semantically motivated sets of base
forms (e.g. V-SPEECH, V-MOVE), and sets of syntactic tags, from which a certain
semantic feature can be inferred ( for cognitive verbs, or N-HUM for {,
}. In principle, semantic tags could be mapped on the basis of such set
membership, blurring the line between (CG) lexicon and (CG) grammar. Instead, for
reasons of consistency, I have treated semantic tags in the same way I have treated
valency and word class tags, by introducing additional information at dictionary level,
integrated into the lexicon entries concerned.
6.2 Semantic prototype tags for nouns:
Minimal distinction criteria
What should semantic tags denote?
It is hard to see how semantic tags could be determined formally (like morphological
tags), or structurally (like syntactic tags), without themselves becoming morphological
or syntactic tags. But then, of course, refining syntactic distinctions is one way of
approaching semantics. For example, I have used valency grouping for sense distinction
in verbs. I think, however, that tagging and the choice of tags, to a certain degree, has to
be goal oriented. So what are semantic tags good for? My own ultimate goal is machine
translation, and so sense distinction in polysemic words is of primary importance.
- 364 -