A syllabifier for Brazilian Portuguese written in foma.
Syllabification is the process of breaking a given word into syllables according to the language's rules, and it helps NLP systems achieve goals such as to map a word into its phonetic transcription, or to generate prosody. Text-to-speech (TTS) systems, the language generation technology behind applications such as virtual assistants and screen readers, often perform syllabification as part of its text pre-processing pipeline, for example.
A few syllabifier algorithms have been proposed for Brazilian Portuguese, including that described in (Silva et al.). Using that as reference, I have implemented the same rules in foma, a finite-state compiler and library.
In their algorithm, the rules are based on the vowel(s) being the nucleus of each syllable, and the algorithm checks each vowel and determines which symbols around it will be considered to form a syllable, and from which those will be separated.
For example, this is the translated pseudocode of the first rule and the examples provided:
if V = p⁰ and V ≠ <ã>,<õ> and ^(+1) = V and ^(+1) != G then Case 1 end ifExamples: a-eronave, a-inda
What the conditional statement says is: if the vowel is in the initial position of a syllable, it is different from ã and õ, and the following symbol (^(+1)) is a vowel (and not a semi-vowel), then it is a Case 1.
The Cases define what will be done with the vowel and the symbols around it; Case 1, for example, means the vowel will be separated from the following symbol.
Thus, the same rule is written in foma as below:
def VowelsExceptÃÕ V .o. ~[ ã | õ ];
def Rule1Case1 [..] -> "-" || VowelsExceptÃÕ _ V;
It is a rewrite rule that will insert a single hyphen ([..] -> "-") into the space between a symbol that matches VowelsExceptÃÕ and another symbol that matches V.
V is the regex that matches vowels, defined based on Table 1 in the paper (translated below). It is defined in the beginning of the syllabifier.foma file. Assuming it has been loaded into foma, this single rule can be compiled as regex on its own and tested:
foma[0]: regex Rule1Case1;
979 bytes. 3 states, 33 arcs, Cyclic.
foma[1]: down aeronave
a-eronave
In this example we see that the rule only matches with one part of the given word, the two first letters, and inserts a hyphen between them.
All the rules have been defined in syllabifier.foma this way, as well as a couple of pre- and post-processing rules, and compiled into the final transducer that takes a word and returns the same word with hyphens where the syllable boundaries are (demonstration in "how to use" section).
The symbols considered as graphemes can be single letters or clusters of letters that should be handled together. For example, ca and ce are in different groups because the consonant c varies in sound depending on the vowel, such as in the words "casa" [kasa] and "cedo" [sɛdu].
| name | definition | symbols |
|---|---|---|
| V | Vowels | a,e,o,á,é,ó,í,ú,ã,õ,â,ê,ô,à,ü |
| G | Semi-vowels | i,u |
| C | All consonants | lh,nh, CO, CF, CL, CN |
| CO | Occlusive consonants | p,t,ca,co,cu,que,qui,b,d,ga,go,gu,gue,gui |
| CF | Fricative consonants | f,v,s,ce,ci,ç,z,ss,ch,j,ge,gi,x |
| CL | Liquid consonants | l except lh, r, rr |
| CN | Nasal consonants | m,n |
* Some other symbols used in the paper such as SP (whitespace) and F (line break) were instead handled as foma-style rules as those will work with only one word at a time.
** Auxiliary regexes have been defined before the relevant rules that need them, for readability purposes.
As organized in the paper, each Case describes which graphemes will be joined with the vowel to form a syllable, or separated.
| case | action |
|---|---|
| Case 1 | Vowel is separated from the next grapheme |
| Case 2 | Vowel is joined with the next grapheme and separated from the subsequent ones |
| Case 3 | Vowel is joined with the previous grapheme and separated from the following |
| Case 4 | Vowel is joined with the previous and the next grapheme and separated from the subsequent ones |
| Case 5 | Vowel is joined with the following 2 graphemes and separated from the 3rd onwards |
| Case 6 | Vowel is joined with the previous grapheme and all the following until the end of the word |
The information on how to install foma is available in its homepage. The syllabifier source can be loaded with the foma command line interface:
foma[0]: source syllabifier.foma
Once loaded, all of the rules and the final Syllabifier transducer will be ready to use. In order to syllabify a word, the apply down shell can be used.
foma[1]: apply down
apply down> aeronave
a-e-ro-na-ve
The same word exemplified before, "aeronave" (aircraft), now matches other rules besides the first one and has all of its syllables correctly separated.
apply down> morfologia
mor-fo-lo-gi-a
apply down> computacional
com-pu-ta-cio-nal
This is a preliminary version of a syllabifier for Brazilian Portuguese that I wrote as an assignment for my Computational Morphology course. It implements all of the rules described in the paper, though some of them can still be improved upon and any issues encountered will be tracked in the Issues tab and hopefully fixed soon. I am also working on implementing validation with a proper word list and ground-truth syllables from dictionaries to evaluate accuracy.
The syllabifier is explicitly proposed for Brazilian Portuguese (BP) and not more generally for the Portuguese language because the rules for dividing syllables vary between BP and European Portuguese (EP) due to phonological variation. For example, some rising diphthongs in BP are realized as vowel hiatus in EP and thus EP separates the hiatus but not BP; the word "série", for example, would be split as "sé-rie" in BP but "sé-ri-e" in EP. For more information, Wikibooks has a list of examples.
D. Silva, D. Braga e F. Resende Jr. 2008. Separação das sílabas e determinação da tonicidade no Português Brasileiro. XXVI Simpósio Brasileiro de Telecomunicações, páginas 1–5.
Mans Hulden. 2009. Foma: a finite-state compiler and library. In Proceedings of the Demonstrations Session at EACL 2009, pages 29–32, Athens, Greece. Association for Computational Linguistics