Eckhard Bick - VISL

4. A blocking context, where the word BARRIER 112 , right after a context with a *position
(an unbounded context), supplies a context condition (tag, tag sequence or set),
that must not appear before the context in question, as calculated from the (absolute,
relative or linked) position that defines the starting point for the search. (*1 VFIN
BARRIER CLB), for instance, looks for a finite verb (VFIN) anywhere to the right - but
this context condition only counts as true, if there is no interfering clause boundary
(CLB) between position 0 and the finite verb.
MAPPINGS
A MAPPING-rule has the following general form
OPERATION (MAPTAG1 MAPTAG2 ...) (TARGET) IF (CONTEXT 1) ...
A mapping rule adds mapping tags, usually syntactic tags marked by the mappingmarker
@, to those readings (= cohort lines) that contain the target-tag, - provided that
all context conditions apply. This part of a mapping rule (the context test) works exactly
as for the constraint rules.
OPERATION can be:
• MAP: first-time mapping, for those cohort lines, that do not yet contain a tag with the
mapping marker (@). This is the normal way to map syntactic function.
• ADD: mapping is performed regardless of any earlier @-tags on the readings line, in
particular, it will also be applied to words featuring lexical mappings from the
lexicon.
• REPLACE: all tags but the first (usually the base form) are deleted, and replaced by
the mapping tags. REPLACE rules could, to a certain degree, compensate for
mistakes preceding parser modules have introduced on the tag line, but are not
supported in the current CG-2 compiler.
Mapping rules are applied in exactly the order they are listed in, - in contrast to
constraint rules, which are best thought of as taking effect "simultaneously" 113 and can
even be tried several times, until no further disambiguation is possible.
In the case of multi-element tag strings, individual tags or tag combinations trigger
appropriate mapping rules in left-to-right tag order. For example, in the tag string “ser”
V PR 3S IND VFIN, mapping rules targeting the word class V (verb) will come into
112
In cg1, a barrier context would have to be expressed by a “backwards looking” LINK NOT *(-)1 context, making
continued “forward” linking difficult.
113
If one wants to control the order in which constraint rules are applied, this can be achieved by grouping them into several
CONSTRAINTS sections, for example separating safe rules from one or more heuristic levels. In my system, six such levels
are used for morphology, and four for syntax.
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