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From text to speech: The MITalk system
vocalic suffix. The “optional” category is used for all other morphs which permit
spelling changes. Examples are:
e required - scar+ed —scarred
o forbidden - alloy+ing — alloying
e optional - change+able — changeable, change+ing — changing
The spelling changes performed by DECOMP consist of appending a letter,
or changing or deleting the last letter. When a morph is matched to the left end of
a word, the following procedure is used to determine the set of possible spelling
changes: If the matched morph is not a suffix, then no spelling changes are made
and recursion proceeds normally. If the matched morph is a nonvocalic suffix and
the last remaining letter is an i, then the change i —>y is examined. If the matched
morph is a vocalic suffix, then spelling changes are performed by matching a
three-character template against the last two remainder letters and the first letter of
the matched morph.
If the vocalic suffix is es, then a special check is made to determine whether
the letter e should be considered part of the suffix. If the remainder does not end
in ¢, ch, g, i, o, s, sh, x, or z, then the es match is immediately rejected. This
causes the morph s to be the next match; the e is thus moved from the suffix to the
remainder. This rule is motivated by the phonetic properties of the plural suffixes
s and es. The lexicon entry for s gives a pronunciation zz while the entry for es
gives 18 2zz. The rule allows DECOMP to make the appropriate decomposition
of tunes— tune+s rather than tunes— tune+es which is found first. The two
vowels, i and o, are permitted to precede es to enable correct decomposition of
words such as heroes and parties, even though pronunciation is not correct in such
cases; morphophonemic rules are used in a later MITalk module to obtain the
proper pronunciation. |
Table 3-1 shows the set of template patterns and their resulting spelling
change actions. The plus sign (+) in the pattern denotes the boundary between the
suffix and the remainder. A dot (.) in the pattern matches any letter. The pattern
xx matches any doubled letter. The first pattern (from top to bottom of the list)
which matches the current remainder/suffix pair controls the set of changes ap-
plied.
For each possible spelling of the remainder, the following steps are per-
formed:
1. Make the change.
2. Recursively decompose the remainder.
3. If a morph matches the right end of the remainder, check its spelling
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