Finnish Noun Inflection

This exercise is a simplified version of the Finnish Noun Inflection problem on the Beesley&Karttunen book web site. The goal is to build a lexicon that contains Finnish nouns inflected for number and case. To keep the problem reasonably small, we consider only three cases: Singular Nominative, Singular Partitive and Plural Partitive. For the same reason, we only consider two types of nouns: monosyllabic and some bisyllabic stems. Even with these limitations, the problem is challenging because the shape of the endings depends on the shape of the stem and the stems are subject to several regular alternations. This excercise assumes that the student is familiar with xfst replace rules and the syntax of lexc source files.

The Facts

A Finnish noun begins with a stem. In all of the cases below, assume that the stem is identical with the nominative singular. A plural marker, if any, immediately follows the stem. After the stem and the possible plural marker comes one of several possible case endings. We consider only two cases: Nominative and Partitive. Singular nominative has no case marker. For the purpose of this excercise we, assume that the plural and the Partitive endings are:

Table 1: Plural and Partitive Markers
I	Plural marker for cases other than Nominative, realized as i or j
Ta	Partitive Marker marker, realized as ta or a in words containing only back vowels.

The following table illustrates some of the possible combinations with the noun valo 'light'.

Table 3: Examples illustrating morphotactics with valo 'light'.
valo	Nominative Singular. No case ending
valoa	Partitive Singular. The partitive marker Ta is realized here as a
valoja	Partitive Plural. The plural marker I is realized as j here. The partitive marker Ta is realized here as a.

The realization of the T in the Genitive Plural and the Partitive marker depends on the syllable structure of the word. After a monosyllabic stem such as maa 'earth', the T is realized as t as in maata. After a bisyllabic stem such as valo 'light', the T disappears as in valoa.

The plural marker I is realized as j between two vowels, otherwise it is realized as i.

With this information you should be able to write the rules that correctly realize the plural marker and the partitive suffix in all environments.

The remaining problem is that the stem of the noun also undergoes alternations. Consonant Gradation is one that we have already seen and solved. It does not apply in the forms we are considering. We will use only back-vowel stems in order to avoid having to deal with vowel harmony. The other stem alternations, Vowel Rounding, Vowel Lowering, Vowel Dropping, and Vowel Shortening are illustrated in Table 4 below.

Table 4: Stem and suffix alternations
Nom Sg	Gloss	Part Sg	Part Pl
puu	tree	puuta	puita
maa	earth	maata	maita
suo	swamp	suota	soita

tikka	dart	tikkaa	tikkoja
pappi	priest	pappia	pappeja
kukka	flower	kukkaa	kukkia
tutti	pacifier	tuttia	tutteja
kauppa	shop	kauppaa	kauppoja
kuoppa	hole	kuoppaa	kuoppia

jalka	foot	jalkaa	jalkoja
linko	sling	linkoa	linkoja

sopu	harmony	sopua	sopuja
kampa	comb	kampaa	kampoja
piispa	bishop	piispaa	piispoja

vahti	guard	vahtia	vahteja
ilta	evening	iltaa	iltoja
sota	war	sotaa	sotia

Vowel Rounding

Short a is rounded to an o in front of the plural marker I. Examples: tikkaa Partitive Singular, tikkoja Partitive Plural, kamman Genitive Singular, kampojen Genitive Plural, kauppaa Partitive Singular, kauppoja Partitive Plural. This does not happen if the vowel nucleus of the preceding syllable starts with a rounded vowel (o or u). See the rule for Vowel Dropping.

Vowel Lowering

Short i is lowered to e in front of the plural marker I. Examples: vahtia Partitive Singular, vahteja Partitive Plural, pappia Partitive Singular, pappeja Partive Plural. See the rule for Vowel Dropping.

Vowel Dropping

A short a is deleted in front of the plural marker I if the nucleus of the preciding syllable consists of, or begins with, a rounded vowel (u or o). Note the different behavior of kuoppa where the a is dropped and kauppa where the a is rounded to o in the plural. Examples: sotaa Partitive Singular, sotia Partitive Plural, kuoppaa Partitive Singular, kuoppia Partitive Plural.

Vowel Shortening

In front of the plural marker I, the long vowels aa, ee, ii, oo, uu, are shortened to a, e, i, o, u, respectively. The diphthongs uo and ie shorten to o and e, respectively. Examples: puuta Partitive Singular, puita Partitive Plural, suota Partitive Singular, soita Partitive Plural.

The Task

Your task is to write an xfst script that reads the finnish.lexc source file provided below that includes the words mentioned above and assembles them into morphotactically correct underlying Finnish forms. We use the tags +Sg, +Pl, +Nom, +Part for marking number and case on the lexical side. Compile finnish.lexc using the command read lex in xfst. At this point your network should contain pairs such as

kukka+Sg+Part jalka+Pl+Part suo+Pl+Part
kukka Ta jalka I Ta suo I Ta

Secondly, write replace rules for realizing the plural marker, the partitive endings, and the four stem-changing rules sketched above. Combine the suffix realization rules with the stem alternation rules sketched above. Think about how to order the rules. It matters.

Finally, create an xfst script that reads in the lexicon, compiles the rules, and composes the lexicon with the rules leaving the result on the stack. The final result should contain pairs such as

kukka+Sg+Part jalka+Pl+Part suo+Pl+Part
kukka a jalko j a so i ta

etc.

Verfify that the lower side of the lexicon contains the properly inflected surface forms by terminating the script with the command

print lower-words

Here is the lexicon:

# -*- coding: iso-8859-1 -*-
# finnish.lexc

Multichar_Symbols +Sg +Pl +Nom +Part

LEXICON Root
Nouns;

LEXICON Nouns
puu Number;    ! tree
maa Number;    ! earth
suo Number;    ! swamp

tikka Number; ! woodpecker
pappi Number; ! priest
kukka Number; ! flower
tutti Number; ! pacifier
kauppa Number; ! shop
kuoppa Number; ! hole

jalka Number; ! foot
linko Number; ! sling

sopu Number;   ! harmony
kampa Number; ! comb
piispa Number; ! bishop

vahti Number; ! guard
ilta Number; ! evening
sota Number;   ! war

Lexicon Number
+Sg+Nom:0 #;
+Sg:0 Case;
+Pl:I Case;

Lexicon Case
+Part:Ta #;