Eckhard Bick - VISL

An important aspect of the local-global resolvability distinction is that it can be seen as
dynamic: some PP attachment ambiguities may be moved from global (i.e.
unresolvable) to local (i.e. resolvable) by using better rules and more lexical
information, for instance, nominal valency classes.
As a matter of fact, as long as enough lexico-semantic information is provided for
the CG-rule to work on, I even believe that the local-global distinction can be applied to
meaning ambiguity as well. Thus, in my parser, I have been able to resolve certain types
of polysemy and verbal incorporation locally, i.e. through sentence context alone (cp.
chapter 6). Some other meaning ambiguities, like thematic roles, might prove local,
once they are introduced into the tagging scheme, and can be addressed by contextual
rules.
3.1.2 Why tags? - The advantages of the tagging notation
All Constraint Grammar (to date) is implicitly tag-based. In fact, by extending the use of
tags to the realm of syntax, Constraint Grammar has effectively widened the horizon of
what traditionally (in HMM-analysers) was understood as tagging. Specifically, the
term ‘tag’ in grammatical analysis will here be used to designate any word based (wordattached)
alphanumeric string bearing meta-information about the word’s form and
function. Tag notation is not some kind of necessary evil stemming solely from the CGformalism’s
needs, but has a number of important advantages in its own right:
• 1. Information from all levels (morphology, syntax, semantics etc.), both form and
function, can be represented in the same formalism, and interact in the
disambiguation process.
• 2. Tags can be combined/juxtaposed graphically as a text line after the word form,
without confusing parenthesis hierarchies or the like, while also being easier to
manipulate in a data-linguistic context (especially after the text has been
"verticalised").
• 3. Tags make it easier to express ambiguity without graphically or structurally
breaking the sentence context in an analysis. Thus, in an alternative sentence reading,
it is not necessary to repeat those parts of the sentence that are not ambiguous. The
longer the sentence, and the less restrictive the grammar, the bigger the advantage
will be.
• 4. Disambiguation is not an "either-or"-process, and can be accomplished gradually
by eliminating incorrect tags. This way the process has a high tolerance of both
incomplete grammars and incomplete (or grammatically wrong) sentences, making
the system a very robust one. Output like "no parse" or "time out", as known from
classical generative grammar, is virtually unthinkable.
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