Eckhard Bick - VISL

Base forms ("...") are tags like all others, only word forms may not be used (they have
their own place, in the beginning of the rule, cp. above). Instead of rewriting the same
rule for several targets, these can be combined by using the set convention 110 :
SELECT NOMINAL IF (-1C DET) ;
where NOMINAL has been defined as N, A, PCP, and the context condition demands
an unambiguous ('C' for 'careful') determiner at the neighbouring position to the left (-
1).
CONTEXT:
Contexts are delimited by parentheses, and by default AND-linked, that is, they must all
apply at the same time, if the rule is to be used (true). A complete context consists of the
following:
1. A position information, consisting of a number denoting the relative position to the
left (-) or right (+), where (or from where) the context condition is to be checked. NOT
can be added in front, and will negate the context condition. An asterisk (*) before the
position number means "unbounded context", i.e. the condition applies all the way left
(-) or right (+) of the position given (absolute or LINKed), - even if the search for a
fitting context should cross the TARGET position (position 0) 111 . For non-negated
(positive) contexts, only the first instance of the context condition will be instantiated
(used for matching the rest of the rule), unless one uses the double asterisk (**), which
makes the rule checker search all the way to a DELIMITER, even in non-negated
contexts. An at-sign (@) before the position number means an absolute context, @1, for
instance, refers to the first cohort, @-2 to the last but one cohort in the sentence.
2. A context condition, consisting of a set, a tag or a tag sequence (the last two in
parentheses), which again can be linked by the operators OR (union), + (concatenation
within the same reading) or AND (intersection of two tags from the cohort). A C
(careful) directly after the position number means that the context condition must be
the cohort's only tag. (-1C N), for instance, means a safe (= fully diambiguated) noun
reading one position to the left. If the word to the left has a, say, (V)-reading at the same
time, the context can not be instantiated (is not true).
3. A linked (complex) context, where the word LINK "hooks up" 2 contexts (within
the same context parenthesis). The second context's relative position is calculated from
the first context's instantiated position, which becomes the new "0-position". This way
one can build long context chains (where all the LINKed contexts are oriented towards
the same side, either right (+) or left (-). Also zero-links (adding more conditions to an
instantiated context) are allowed.
110 In terma of rule writing efficiency, not allowing for sets in targets is one of the main disadvantages of the older cg1.
111 In the cg1 compiler, an unbounded search would not pass the target (0) position, accounting for one of the more
substantial incompatibilities between cg1 and cg1.
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