Constraint-based grammars

IPOX constraint-based grammars define:

categories and features
macro's
templates
initial category
phrase structure rules
lexicon

Below, some examples are given of each rule type. The examples serve only as an illustration, they are not intended as an analysis of a particular language.

Categories and features:

   Word => edge.
   Foot => edge.
   Syl => edge, stress.
   ...
   vow => stress, voc.

   edge => ini, fin.
   voc => grv, rnd, height.

Note: only the complex feature structures edge and voc need a separate definition.

Macro's:

   FRONT := [voc:[-grv, -rnd]].
   SPREAD := [voc:[+grv, -rnd]].
   ROUND := [voc:[+grv, +rnd]].

   HIGH := [voc:[height=close]].
   MID := [voc:[height=mid]].
   LOW := [voc:[height=open]].

Note: macro's such as these can be used to make a grammar more readable, easier to modify, as well as to express the fact that there are no front, rounded vowels.

Templates:

Templates are general descriptions of different kinds of constituents:

branching constituents
non-branching constituents
terminal or empty constituents
constituents with a weak-strong pattern
constituents with a strong-weak pattern

Branching or non-branching:

   [edge:[ini=A, fin=B]] --> [edge:[ini=A, -fin]], [edge:[-ini, fin=B]].
   [edge=A] --> [edge=A].
   [stress=A] --> [stress=A].

Weak-strong or strong-weak:

   [stress=A] --> ([] / [stress=A]).
   [stress=A] --> ([stress=A] \ []).

Note: the feature edge is used to mark the left and right edges of a structure; the feature stress is a head-feature of all categories which define the feature.

Initial category:

   Word:[edge:[+ini, +fin]].

Note: the top-level goal for the parser; the feature edge is assigned the interpretation of "edge of a word".

Phrase-structure rules:

   Word --> (Foot / Word).
   Word --> Foot.

   Foot:[edge:[+fin]] --> ((Syl:[+stress] \ Syl:[-stress]) \ Syl:[-stress]).
   Foot --> (Syl:[+stress] \ Syl:[-stress]).
   Foot:[edge:[+ini]] --> Syl.

   Syl --> (On / Ri).
   ... etc.

Notes: in this grammar, the main stress occurs in either the ante-penultimate or the penultimate syllable; a monosyllabic foot is allowed only word-initially.

Lexicon:

   vow:[FRONT, HIGH] --> "i".
   vow:[-stress, SPREAD, MID] --> "@".

Notes: the macro's are expanded during compilation; if all categories between Syl and vow are defined for the feature stress, the templates will assure that schwa can only occur in unstressed syllables.

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Arthur Dirksen / adirksen@prl.philips.nl / January 1995