Data structure

The main data structure of IPOX is the metrical tree, or, more generally, a binary-branching, headed tree.

Type definition

Tree :: Node --> Tree

| ( Tree / Tree )
| ( Tree \ Tree )
| Terminal

In this definition, the slash is used to indicate which of two sister nodes is the (prosodic) head.

Graphic representations

• conventional metrical tree: only weak-strong or strong-weak is indicated; unary nodes are ignored
• headed constituent tree: constituent labels are shown, as well as headedness

Example

two representations of the prosodic structure of the word photographical:

metrical tree headed tree

Internal representation

W --> 
      (F --> (S --> "pho" \ S --> "to") 
      / F --> ((S --> "gra" \ S --> "phi") \ S --> "cal"))

A node in a metrical representation is a complex feature structure (Shieber 1986).

Type definition

Node   ::  Category:Features

   Features :: [FV*]

   FV     ::  Node
           |  Feature=Value
           |  +Feature          (Feature=true)
           |  -Feature          (Feature=false)

Example

complex feature structure for the unstressed vowel schwa

vow:[-stressed, voc:[+back, -rnd, height=mid]]

Our data structure is not limited to the representation of prosodic headedness.

Other uses

• syntactic headedness:

  VP --> (V \ NP)

• morphological structure:

  word --> ((prefix / root) \ suffix)

Objection

Our data structure is too general because prosodic structure is "flat", that is, non-recursive (Nespor and Vogel 1986).

Defense

• self-embedding is OK if across the board , as in (a) below
• self-embedding is compiled away in (b), obtaining (c)
• a prosodic category may not dominate a category of a higher type

Examples

(a) (b) (c)

stress patterns of two Dutch words: (a) universiteit 'university'; (b=>c) makaroni 'macaroni'