# The Text-TransMetaphone Perl Module

### About this release

By releasing the Text-TransMetaphone package at this time I'm essentially using CPAN for CVS. This is an "in case I get hit by a truck tomorrow" development release. Accordingly, you use it at your own risk. Expect the trans-metaphone package to be in development for quite some time.

### Principles of the Trans-Metaphone Algorithm

The Trans-Metaphone algorithm takes the principle of the Soundex and Metaphone algorithms a step further and attempts to produce "keys" that are comparable across writing systems. The approach fascilitates language independent text retrieval. For example, the algorithm could be applied to find documents in any language that contained a topical word like "taliban"

The Soudex and Metaphone family of algorithms both address the fundamental problem of the transcription of non-English names onto the 26 letter English alphabet. The approach has been applied beyond proper nouns and has retained a good degree of success. It has been extended to account for the in-English problem of representing phonemes in a writing system with an insufficient number of symbols to represent them.

In the course of transcription between writing systems the transcriber goes thru the process of converting symbols into sounds and then back into symbols. In the course of in-language writing the scribe skips the first step and writes sounds with symbols under a given convention. This is largely an unconcious act for writers of any experience.

The Soundex and Metaphone algorithms begin by reversing the in-language writing process converting symbols into sounds and then return to a reduced set of symbols in the initial writing system. The trans metaphone approach attempts to arrest the process at the phonological abstraction. Words of different languages may then be compared based on their phonemic pattern.

This is the notion at least. We still depend on symbols to represent sequences of phonemes so a final transcription step from phonemese to symbols still occurs. Only this time the International Phonetic Alphabet (IPA) is used and the character set is Unicode. Simplified keys are still generated to aid comparison and most of the same rules still apply. All but the first vowel in a word will be stripped out. Consonants in the trans metaphone algorithm are not as aggressively reduced to the same key as its predecessors. This is done to retain a higher degree of phonemic grandularity for comparision. This will change over time and is expected to be the primary area of experimentation.

### Folding Script and Generating Keys

The concept of folding script for text comparison was an objective of the Grand Unified Syllabary (GUS) project. The effort was postponed when problems were encountered with UTF-8 breakage in overloaded REs under Perl (since resolved in v5.8). The effort is expected to eventually resume ( /I anyone?). GUS data has been applied in the Text-TransMetaphone package.

Strictly speaking the trans metaphone algorithm does not fold script but like the other members of its family reduces strings to a simplified form for comparison. Key representations allow for a matches to be made between like words with different spellings (and now spellings in different writing systems).

Each module under the Text::TransMetaphone:: namespace has the responsibility of generating an IPA key (or keys) for a given language or dialect. The modules are named accordingly following locale conventions. For example, Text::TransMetaphone::en_US will create keys for English as spoken in the United States. Incidently, the en_US module is a version of the Text::DoubleMetaphone module modified to return keys in IPA notation. Remember that we are working with written language and not spoken language. While regional difference in spoken English occur within the US, written English is standardized. An en_UK module might be practical as minor difference do occur between UK and US written English.

The Text::TransMetaphone:: modules have only the responsibility of generating keys for words of the writing system used by the language. Seperate modules should be made for languages using more than one writing system (::ja_hiragana and ::ja_katakana for example). The modules will implement a `trans_metaphone` function that accepts a single string, converts it into an IPA sequence, parsing as per the orthography conventions of the langage, and retuns as many keys as deemed appropriate. In short, each module acts like an independent N-Metaphone module for a specific language applying IPA notation.

Additionally, it is required that each module contain a local `$LocaleRange` quoted RE that identifies the Unicode character range that it is accepts. The RE will later be used by the Text::TransMetaphone class as a guess value to associate a string with a module when no locale has been specified for the string.

While not required, it is recommended that each module also provide a `reverse_key` function. The `reverse_key` function accepts a string of IPA sequences and will transliterate the sequence into the native writing system. This function should generally be simple to implement and may be of some limited practical value.

### Double Trouble

The trans-metaphone algorithm allows the language specific key generators to return as many keys as deemed appropriate. The only restriction imposed is that the first key returned should be the canonical (or literal conversion) and later keys should be in order of decreasing likelihood. This is in keeping with the approach of th double-metaphone algorithm. It is recommended that the final key be a regular expression that would match any of the returned keys. This is considered an experimental aspect of the algorithm.

The trans-metaphone algorithm does depart from the double-metaphone algorithm in one other importan aspect. The secondary key in the double metaphone algorithm is also the most permuted key that could be created. That is, the secondary key contains substitutions for every letter that could be substituted. This is probably not much of an issue for English where only one secondary substitution may occur in a word. The trans-metaphone approach at this time is a little more cautious and will return one key for each substitution made. The last key will contain all secondary substitutions together and will be analogous to the double metaphone secondary key. For example:

ABC | Initial String
APK | Primary Key
AXK | Secondary Key for B
APY | Secondary Key for C
AXY | Secondary Keys for B & C
A[PX][KY] | Terminal Regex Key

Accordingly the number of returned keys will always be one greater than some power of two. A table of the mappings of character sequences to IPA symbols with references is available here.

### The Problem with Phonology

<rant level="11">
The problem with phonology is that no two people speak alike. Generally, this is accepted as a good thing and likely prevents more confusion form occuring than it creates. Inescapably, phonology surveys reflect a the intonations of a small sample of speakers from a given population. Given the nature of language we end up with different phonemic inventories for speakers of the same language when different regions are surveyed. Fortunately this fits in with the locale model and any time you are find a population that talks funny, you can assign them their own "special" locale.

The real problem with phonology is that it is all in the ear of the beholder. Not to mention the training of the beholder. Surveyers of different experience levels can easily come up with different results for the same test subjects. Phonology tables for a given language that you might find from 10, 20, 50 or 100 years ago will all use different symbology conventions. The present day isn't much better. The IPA helps, when people use it, but even from one chapter to the next in the IPA handbook we find surveyor recording the same phonemes with different symbol choices.

They do this to hurt me... These discrepancies ultimately will not impact the keys generated with the trans metaphone algorithm since the keys represent an approximation, a phomeic range and not a precise point. Development of the trans metaphone algorithm is slowed down however by the unlike symbology conventions.
</rant>

### Help Wanted

If you are knowledgable in the writing conventions of a partially or unsupported language and get your kicks tinkering with phonology, orthography, transliteration and transcription..