7. Adding Support For Other Languages

Before you consider adding support for Aspell first make sure that someone else has not already done it. A good number of dictionaries off the Aspell home page at http://aspell.net. If your language is not listed above please send me a note and I will work with you on adding support.

This chapter describes the old manual way of adding support for a new language in Aspell. The recommended way to add support is through the aspell-dicts package. The scripts used, as well as some documentation on what to do, is available in the aspell-gen package which is available in the same location the dictionary packages are at.

Adding a language to aspell is fairly straightforward. You need to create the language data file, and compile a new word list.

7.1 The Language Data File

The basic format of the language data data is the same as it for aspell configuration file. It is named «lang».dat and is located in the architecture independent data dir for aspell (option data-dir) which is usually «prefix»/share/aspell. Use ``aspell config'' to find out where it is in your installation. By convention the language name should be the two letter ISO 639 language code.

The language data file has several mandatory fields, and several optional ones. All fields are case sensitive and should be in all lower case.

The two mandatory fields are name and charset. Name is the name of the language and should be the same as the file name (without the .dat). Charset is the charset aspell will expect the word lists to be formatted in. You may chose from any of the iso-8859-* character sets as well as, koi8-f, koi8-r, and viscii. If your language can fit in the plain old ASCII character set use iso8859-1. If you use some other character set for your language other than the ones listed here drop me a note and I will look into adding support for it.

The optional fields are special, soundslike, keyboard and a bunch of options to specify how run-together words are handles. Special is for non letter characters that can appear in your language such as the ' and -. The format for the value is a list separated by spaces. Each item of the list has the following format

«char»  «begin»«middle»«end»

«char» is the non letter character in question. «begin»,«middle»,«end» are either a '-' or a '*'. A star for «begin» means that the character at the beginning of the word, a '-' means it can't. The same is true for «middle» and «end». For example the entry for the ' in english is:

' -*-

To include more than one middle character just list them one after another on the same line. for example to make both the ' and the - a middle character use the following line in the language data file:

special ' -*- - -*-

The soundslike option, if present, should be the name of the soundslike data for the language. The data is expected to be in the file «name»_phonetic.dat.

If the name is generic a really generic soundslike algorithm will be used which consists of striping all the vowels and removing all accents. I recommend first using the generic algorithm and then, after aspell is working with the new language, work on the transformation array.

If the soundslike name is none then no soundslike lookup table will be used. This will reduce the size of the compiled word list by around 50% but at the sacrifice of suggestion quality. If the soundslike is none than the soundslike for the word will simply be the word itself in lowercase, will all accents stripped. For languages with phonetic spelling the difference will not be very noticeable. However, for languages with non-phonetic spelling there will be a noticeable difference. The difference you notice will depend on the quality of the soundslike data file. If you do not notice much of a difference for a language with non-phonetic spelling that is a good indication that the soundslike data is not rough enough--or the words you are trying are not that badly misspelled.

The keyboard option specifies the base name of the keyboard definition file to use. See section 4.4.3 for more information.

The options to control how run-together words are handled are the same as the are in the normal configurations files. Please see section 7.4 for more information.

7.2 Compiling the Word List

Once you have a working language data file installed in the right place you are ready to compile the main word list. See section 5 to find out what to do. This section also includes instructions for creating the awli file.

7.3 Phonetic Code

(The following section was written by Björn Jacke, bjoern.jacke at gmx de)

Aspell is in fact the spell checker that comes up with the best suggestions if it finds an unknown word. One reason is that it does not just compare the word with other words in the dictionary (like Ispell does) but also uses phonetic comparisons with other words.

The new table driven phonetic code is very flexible and setting up phonetic transformation rules for other languages is not difficult but there can be a number of stumbling stones -- that's why I wrote this section.

The main phonetic code is free of any language specific code and should be powerful enough to allow setting up rules for any language. Anything which is language specific is kept in a plain text file and can easily be edited. So it's even possible to write phonetic transformation rules if you don't have any programming skills. All you need to know is how words of the language are written and how they are pronounced.

7.3.1 Syntax of the transformation array

In the translation array there are two strings on each line; the first one is the search string (or switch name) and the second one is the replacement string (or switch parameter). The line

version   «version»

is also required to appear somewhere in the translation array. The version string can be anything but it should be changed when ever the a new version of the translation array is released. This is important because it will keep Aspell from using a compiled dictionary with the wrong set of rules. For example if when coming up with suggestion for ``hallo'' aspell will use the new rules to come up with the soundslike say ``H*L*'' but if hello is stored in the dictionary using the old rules as ``HL'' instead of ``H*L*'' aspell will never be able to come up with hello. So to solve this problem Aspell checks if the version strings match and abort with an error if they don't. Thus it is important to update it when ever a new version of the translation array is releases. This is only a problem with the main word list as the personal word lists are now stored as simple word lists with a single header line (ie, no soundslike data).

Each non switch line represents one replacement (transformation) rule. Words beginning with the same letter must be grouped together; the order inside this group does not depend on alphabetical issues but it gives priorities; the higher the rule the higher the priority. That's why the first rule that matches is applied. In the following example:

GH     _  
G      K  
 

``GH to _'' has higher priority than ``G to K''. ``_'' represents the empty string ``''. If ``GH to _'' would stand after ``G to K'', the second rule would never match because the algorithm would stop searching for more rules after the first match. The above rules transform any ``GH'' to an empty string (delete them) and transform any other ``G'' to ``K''.

At the end of the first string of a line (the search string) there may optionally stand a number of characters in brackets. One (only one!) of these characters must fit. It's comparable with the [ ] brackets in regular expressions. The rule ``DG(EIY) to J'' for example would match any ``DGE'', ``DGI'' and ``DGY'' and replace them with ``J''. This way you can reduce several rules to one.

Behind the search string there can stand one or more dashes (-). Those search strings will be matched totally but only the beginning of the string will be replaced. Furthermore for these rules no follow-up rule will be searched (what this is will be explained later). The rule ``TCH-- to _'' will match any word containing ``TCH'' (like ``match'') but will only replace the first character ``T'' with an empty string. The number of dashes determines how many characters from the end will not be replaced. After the replacement the search for transformation rules continues with the not replaced ``CH''!

If a ``<'' is appended to the search string, the search for replacement rules will continue with the replacement string and not with the next character of the word. The rule ``PH< to F'' for example would replace ``PH'' with ``F'' and then again start to search for a replacement rule for ``F...''. If there would also be rules like ``FO to O'' and ``F to _'' then words like ``PHOXYZ'' would be transformed to ``OXYZ'' and any occurrences of ``PH'' that are not followed by an ``O'' will be deleted like ``PHIXYZ to IXYZ''. The second replacement however is not applied if the priority of this rule is lower than the priority of the first rule.

Priorities are added to a rule by putting a number between 0 and 9 at the end of the search string, for example ``ING6 to N''. The higher the number the higher is the priority.

Priorities are especially important for the previously mentioned follow-up rules. Follow-up rules are searched beginning from the last string of the first search string. This is a bit complicated but I hope this example will make it more clear:

CHS      X 
CH       G 
 
HAU--1   H 
 
SCH      SH 
 

In this example ``CHS' in the word ``FUCHS'' would be transformed to ``X''. If we take the word ``DURCHSCHNITT'' the things look a bit different. Here ``CH'' belongs together and ``SCH'' belongs together and both are spoken separately. The algorithm however first finds the string ``CHS'' which may not be transformed like in the previous word ``FUCHS''. At this point the algorithm can find a follow up rule. It takes the last character of the first matching rule (``CHS'') which is ``S'' and looks for the next match, beginning from this character. What it finds is clear: It finds ``SCH to SH'', which has the same priority (no priority means standard priority, which is 5). If the priority is the same or higher the follow-up rule will be applied. Let's take a look at the word ``SCHAUKEL''. In this word ``SCH'' belongs together and may not be torn apart. After the algorithm has found "SCH to SH" it searches for a follow-up rule for "H"+"AUKEL". It finds "HAU--1 to H", but does not apply it because its priority is lower than the one of the first rule. You see that this is a very powerful feature but it also can easily lead to mistakes. If you really don't need this feature you can turn it off by putting the line

followup      0 

at the beginning of the phonetic table file. As mentioned, for rules containing a `-' no follow-up rules are searched but giving such rules a priority is not totally senseless because they self can be follow-up rules and in that case the priority makes sense again. Follow-up rules of follow-up rules are not searched because this is in fact not needed very often.

The control character "^" says that the search string only matches at the beginning of words so that the rule "RH^to R" will only apply to words like "RHESUS" but not "PERHAPS". You can append another "^" to the search string. In that case the algorithm treats the rest of the word totally separately from first matched string in at beginning. This is useful for prefixes whose pronunciation does not depend on the rest of the word and vice versa like "OVER^^" in English for example.

The same way as "^" works does "$" only apply on words that end with the search string. "GN$ to N" only matches on words like "SIGN" but not "SIGNUM". If you use "^" and "$" together, both of them must fit "ENOUGH^$ to NF" will only match the word "ENOUGH" and nothing else.

Of course you can combine all of the mentioned control characters but they must occur in this order: < - priority ^ $. All characters must be written in CAPITAL letters.

If absolutely no rule can be found -- might happen if you use strange characters for which you don't have any replacement rule -- the next character will simply be skipped and the search for replacement rules will continue with the rest of the word.

If you want double letters to be reduced to one you must set up a rule like "LL- to L". If double letters in the resulting phonetic word should be allowed, you must place the line

collapse_result     0 

at the beginning of your transformation table file; otherwise set the value to `1'. The English rules for example strip all vowels from words and so the word "GOGO" would be transformed to "K" and not to "KK" (as desired) if collapse_result is set to 1. That's why the English rules have collapse_result set to 0.

7.3.2 How do I start finally?

Before you start to write an array of transformation rules, you should be aware that you have to do some work to make sure that things you do will result in correct transformation rules.

7.3.2.1 Things that come in handy

First of all you need to have a large word list of the language you want to make phonetics for. It should contain about as many words as the dictionary of the spell checker. If you don't have such a list, you will probably find an Ispell dictionary at http://fmg-www.cs.ucla.edu/geoff/ispell-dictionaries.htmlwhich will help you. You can then make affix expansion via ispell -e and then pipe it trough \tr " " "\n" to put one word on each line. After that you eventually have to convert special characters like `é' from Ispell's internal representation to latin1 encoding. sed s/e'/é/g for example would replace all e' with é.

The second is that you know how to use regular expressions and know how to use grep. You should for example know that

grep ^[^aeiou]qu[io] wordlist | less

will show you all words that begin with any character but a, e, i, o or u and then continue with `qui' or `quo'. This stuff is important for example to find out if a phonetic replacement rule you want to set up is valid for all words which match the expression you want to replace. Taking a look at the regex(7) man page is a good idea.

7.3.2.2 What the phonetic code should do

Normal text comparison works well as long as the typer misspells a word because he pressed one key he didn't really want to press. In this cases mostly one character differs from the original word.

In cases where the writer didn't know about the correct spelling of the word however the word may have several characters that differ from the original word but usually the word would still sound like the original word. Someone might think for example that `tough' is spelled `taff'. No spell checker without phonetic code will come to the idea that this might be `tough' but a spell checker who knows that `taff' would be pronounced like `tough' will make good suggestions to the user. Another example could be `funetik' and `phonetic'.

From this examples you can see that the phonetic transformation should not be too fussy and too precise. If you implement a whole phonetic dictionary as you can find it in books this will not be very useful because then there could still be many characters differing from the misspelled and the desired word. What you should do if you implement the phonetic transformation table is to reduce the number of used letters to the only really necessary ones.

Characters that sound similar should be reduced to one. In English language for example `Z' sounds like `S' and that's why the transformation rule ``Z to S'' is present in the replacement table. `PH' is spoken like `F' and so we have a ``PH to F'' rule.

If you take a closer look you will even see that vowels sound very similar in English language: `contradiction', `cuntradiction', `cantradiction' or `centradiction' in fact sound nearly the same, don't they? Therefore the English phonetic replacement rules not only reduce all vowels to one but even remove them all (removing is done by just setting up no rule for those letters). The phonetic code of `contradiction' is `KNTRTKXN' and if you try to read this letter-monster loud you will hear that it still sound a bit like `contradiction'. You also see that `D' is transformed to `T' because they nearly sound the same.

If you think you have found a regularity you should always take your word list and grep for the corresponding regular expression you want to make a transformation rule for. An example: If you come to the idea that all English words ending on `ough' sound like `AF' at the end because you think of `enough' and `tough'. If you then grep for the corresponding regular expression by ``grep -i ough$ wordlist'' you will see that the rule you wanted to set up is not correct because the rule doesn't fit to words like `although' or `bough'. So you have to define your rule more precisely or you have to set up exceptions if the number of words that differ from the desired rule is not so big.

Don't forget about follow-up rules which can help in many cases but which also can lead to many confusions and side effects. It's also important to write exceptions in front of the more general rules ("GH" before "G" etc.).

If you think you have set up a number of rules that may produce some good results try them out! If you run Aspell as ``aspell --lang=«your language» pipe'' you get a prompt at which you can type in words. If you just type words Aspell checks them and eventually makes suggestions if they are misspelled. If you type in ``$$Sw «word»'' you will see the phonetic transformation and you can test out if your work does what you want.

Another good way to control if changes you apply to your rules don't have any evil side effects is to create another list from your word list which contains not only the word of the word list but also the corresponding phonetic version of this word on the same line. If you do this one time before the change and one time after the change you can make a diff (see man diff) to see what really changed. To do this use the command ``aspell --lang=«your language» soundslike''. In this mode aspell will output the the original word and then its soundslike separated by a tab character for each word you give it. If you are interested in seeing how the algorithm works you can download a set of useful programs from http://members.xoom.com/maccy/spell/phonet-utils.tar.gz. This includes a program that produces a list as mentioned above and another program which illustrates how the algorithm works. It uses the same transformation table as Aspell and so it helps a lot during the process of creating a phonetic transformation table for Aspell.

During your work you should write down your basic ideas so that other people are able to understand what you did (and you still know about it after a few weeks). The English table has a huge documentation appended for example.

Now you can start experimenting with all the things you just read and perhaps set up a nice phonetic transformation table for your language to help Aspell to come up with the best correction suggestions ever seen also for your language. Take a look at the Aspell homepage to see if there is already a transformation table for your language. If there is one you might also take a look at it to see if it could be improved.

If you think that this section helped you or if you think that this is just a waste of time you can send any feedback to bjoern.jacke@gmx.de.

7.4 Controlling the Behavior of Run-together Words

Aspell has support for either unconditionally accepting run-together words or only accepting certain words in compound formation.

Support for unconditionally accepting run-together words can either be turned on in the language data file or as a normal option via the run-together option. The run-together-limit options controls the maximum number of words that can be strung together, the default is normally 255. The run-together-min options controls the minimal length the individual components of the run together word can be, the default is normally 3. Both the run-together-limit and run-together-min option may be specified in both the language data file or as a normal. The run-together-mid option, which may only be specified in the language data file, may be used to specify up to three optional characters that may appear between individual words.

In order for aspell to conditionally only accept certain words in compounds those words must be flagged when the compiled word list is being created. The format for each entry is

«word»:C[1][2][3]«middle char»

The 1, 2, and 3 control if the word is allowed to appear in the begging, middle, or end of the compound, respectfully. More than one position flag may be specified. If none of them are specified it as assumed that the word may appear anywhere. The C is optional if 1, 2, or 3 is specified. The «middle char» represents an optional character that may appear after the word in the formation of the compound if the word is not at the end of the compound. If the letter is lowercase than the character may appear after the word, if it is in uppercase then that letter must appear after the compound. Only one letter may be specified and it must also be in the list of middle letters specified via the run-together-mid option. The run-together-limit option may also be used to specify the maximum number of words to string together.

For example the word list:

beg:1
mid:2
end:3
any:C
never
must:CM
maybe:Cm

Means that the word ``beg'' may only appear at the begging of a word, the word ``mid'' at the middle, the word ``end'' at the end, and the word ``any'' any place. The word ``never'' is never accepted in a compound unless the run-together option is set. The word ``must'' may appear anywhere however it must be followed by an ``m'', while the word maybe may be followed by an ``m''. Given the above word list the following compounds or legal:

begmidend
begany
mustmend
maybeend
maybemend

are all legal, but the following are not:

begmid
mustend
neverany

Individual words such as ``beg'' are always accepted.

When the run-together option is not set Aspell will only accept words that have been flagged in a run-together word. When the run-together option is set aspell will accept words which are as least as long as the value specified in the run-together-min option. If the words length is less than run-together-min then it will only accept the word if it has been flagged. When the run-together option is not set the run-together-min option is ignored all together.

Currently Aspell only supports run-together words when checking if a word is in the dictionary. When coming up with suggestions Aspell treats the word as a normal word and does not do anything special. This means that the suggestions will be virtually meaningless when the actual word is a run-together. I plan on more intelligently supporting run-together words when coming up with suggestions in a future version of Aspell.