Linguistic Modeling for Multilingual Machine Translation

14 CHAPTER 2. CAT2: FORMALISM AND DESIGN
variable binding
b-rules
in the grammar rule is instantiated in the object, as shown in the following
example 14 .
(10)
lex=mann,
object1:
head= cat=n
F
n o
rule: frame= arg1= role=nil
=)
8
9
lex=mann,
><
>=
head=
cat=n ,
object2: n o
>: frame= arg1= role=nil
>
Following Prolog convention, logical variables beginning with upper-case letters
can be used to bind twovalues within one object (cf. [W.F. and C.S.84]). Once
avariable is instantiated by unication, all other variables bound to it become
equally instantiated and share all the same constraints. Variables can refer
to a feature structure within a node (11), just as to a complete node in a
tree structure (12). In (12) the value of the attribute must unify with the
adjacent nodeinthetree. Given such a construct, it is easy, for example, to
state subcategorization requirements in one element thatmust be fullled by
an adjacent element.
(11)
" #
attribute=VAR
::: attribute=VAR
(12)
:::
attribute=VAR
VAR
The described type of data structure, i.e. tree structures with annotated feature
bundles, are used in ve types of rules. These rules are called b-rules, f-rules,
l-rules, t-rules and tf-rules.
b-rules (i.e. building rules) describe the valid tree structures for every level of
representation. They correspond to the re-writing rules of generative grammars
or the immediate dominance schemata of HPSG with the dierence that b-
rules specify not only the immediate dominance, but also the linear precedence,
i.e. the linear order of elements in time or space. The rewriting rule S-> NP,
VP could be expressed in CAT2 as:
14 For purposes of presentation I use F as the unication operator and =) for designating
the outcome of this operation.