Patent Application
20070219777
The discussion below is merely provided for general background information and is not intended to be used as an aid in determining the scope of the claimed subject matter.
Using by way of example speech synthesis, text-to-speech technology allows computerized systems to communicate with users using synthesized speech. Some speech synthesizers use letter-to-sound (LTS) conversion to generate the pronunciation of out of the vocabulary (OOV) words. Person names are commonly OOV as well as may originate from other languages. This is true, for example, with English where many person names originate from other languages and their pronunciations are heavily influenced by the rules in the original languages. Therefore, the accuracy of name pronunciation generated from a typical English LTS is normally low. To improve the performance, identifying language origin of a word can be critical.
Language identification has been done for spoken languages. Using one technique, a speech utterance is first converted into a phoneme string by a speech recognition engine, then the probabilities that the phoneme string belongs to each candidate language are estimated by phoneme N-grams of that language, and finally the language with the highest likelihood is selected. Language identification has been also performed on web documents, in which more information such as HTML (Hyper Text Mark-up Language) tag and special letters in different languages can help a lot.
However, the task of identifying language origin of person names in a language, particularly, English can be more difficult during text conversion because all non English characters are normally converted into similar English characters. For example, the German name ‘Andra’ is written as Andra in English and the French name ‘Aime’ is written as Aime. Hence, many times the letter string is the only information available.
Letter based N-grams have also been used with some success to identify the language origin of names among several candidate languages given a letter string. Typically, a letter based N-gram model has to be trained for each candidate language beforehand. When a new name is analyzed, it will be scored by all letter based N-grams and the language for the letter based N-gram having the highest likelihood will be output as the language hypothesis. Although this technique can be used to hypothesize the language of origin of a word, room exists for improvement when determining language origin from a letter string.
This Summary and Abstract are provided to introduce some concepts in a simplified form that are further described below in the Detailed Description. This Summary and Abstract are not intended to identify key features or essential features of the claimed subject matter, nor is it intended to be used as an aid in determining the scope of the claimed subject matter. In addition, the description herein provided and the claimed subject matter should not be interpreted as being directed to addressing any of the short-comings discussed in the Background.
Language of origin analysis of a word includes analyzing non-uniform letter sequence portions of the word. N-gram models based on these chunks are trained for: each language under consideration. Various criteria can be used as a basis for determining the letter chunks. These criteria include but are not limited letter chunks determined using MDL (Minimum Description Length), LZ (Lempel-Ziv) or a closed set. In addition, a new criterion herein described includes syllable-based letter chunks (SBLC). SBLCs are generated by syllabification of letter strings according to the known syllable structure in phoneme strings. Since error distributions from different N-grams can be quite different, they can be combined to achieve more accuracy. One form of combined classifier that can be used is a classifier employing adaptive boosting.
One general concept herein described provides for the analysis of a word to hypothesize the language of origin. Analysis includes analyzing non-uniform letter sequence portions of the word. In a further embodiment, analysis includes using N-grams having frequently used letter clusters or chunks. As one criterion, syllable-based letter chunks (SBLC) herein described are used. SBLCs are generated by syllabification of letter strings according to the known syllable structure in phoneme strings. Since the number of possible syllables in languages like English can be very large, in one embodiment, only the most important SBLCs will be selected with respect to the overall coverage of syllables in the language. Although the examples described herein use the Roman alphabet, it should be understood this is not a limitation and that form of alphabet can be used.
However, before describing further aspects, it may be useful to first describe exemplary computing devices or environments that can implement the description provided below.
In addition to the examples herein provided, other well known computing systems, environments, and/or configurations may be suitable for use with concepts herein described. Such systems include, but are not limited to, personal computers, server computers, hand-held or laptop devices, multiprocessor systems, microprocessor-based systems, set top boxes, programmable consumer electronics, network PCs, minicomputers, mainframe computers, distributed computing environments that include any of the above systems or devices, and the like.
The concepts herein described may be embodied in the general context of computer-executable instructions, such as program modules, being executed by a computer. Generally, program modules include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Those skilled in the art can implement the description and/or figures herein as computer-executable instructions, which can be embodied on any form of computer readable media discussed below.
The concepts herein described may also be practiced in distributed computing environments where tasks are performed by remote processing devices that are linked through a communications network. In a distributed computing environment, program modules may be located in both local and remote computer storage media including memory storage devices.
With reference to
Computer 110 typically includes a variety of computer readable media. Computer readable media can be any available media that can be accessed by computer 110 and includes both volatile and nonvolatile media, removable and non-removable media. By way of example, and not limitation, computer readable media may comprise computer storage media and communication media. Computer storage media includes both volatile and nonvolatile, removable and non-removable media implemented in any method or technology for storage of information such as computer readable instructions, data structures, program modules or other data. Computer storage media includes, but is not limited to, RAM, ROM, EEPROM, flash memory or other memory technology, CD-ROM, digital versatile disks (DVD) or other optical disk storage, magnetic cassettes, magnetic tape, magnetic disk storage or other magnetic storage devices, or any other medium which can be used to store the desired information and which can be accessed by computer 110. Communication media typically embodies computer readable instructions, data structures, program modules or other data in a modulated data signal such as a carrier WAV or other transport mechanism and includes any information delivery media. The term “modulated data signal” means a signal that has one or more of its characteristics set or changed in such a manner as to encode information in the signal. By way of example, and not limitation, communication media includes wired media such as a wired network or direct-wired connection, and wireless media such as acoustic, FR, infrared and other wireless media. Combinations of any of the above should also be included within the scope of computer readable media.
The system memory 130 includes computer storage media in the form of volatile and/or nonvolatile memory such as read only memory (ROM) 131 and random access memory (RAM) 132. A basic input/output system 133 (BIOS), containing the basic routines that help to transfer information between elements within computer 110, such as during start-up, is typically stored in ROM 131. RAM 132 typically contains data and/or program modules that are immediately accessible to and/or presently being operated on by processing unit 120. By way of example, and not limitation,
The computer 110 may also include other removable/non-removable volatile/nonvolatile computer storage media. By way of example only,
The drives and their associated computer storage media discussed above and illustrated in
A user may enter commands and information into the computer 110 through input devices such as a keyboard 162, a microphone 163, and a pointing device 161, such as a mouse, trackball or touch pad. Other input devices (not shown) may include a joystick, game pad, satellite dish, scanner, or the like. These and other input devices are often connected to the processing unit 120 through a user input interface 160 that is coupled to the system bus, but may be connected by other interface and bus structures, such as a parallel port, game port or a universal serial bus (USB). A monitor 191 or other type of display device is also connected to the system bus 121 via an interface, such as a video interface 190. In addition to the monitor, computers may also include other peripheral output devices such as speakers 197 and printer 196, which may be connected through an output peripheral interface 190.
The computer 110 may operate in a networked environment using logical connections to one or more remote computers, such as a remote computer 180. The remote computer 180 may be a personal computer, a hand-held device, a server, a router, a network PC, a peer device or other common network node, and typically includes many or all of the elements described above relative to the computer 110. The logical connections depicted in
When used in a LAN networking environment, the computer 110 is connected to the LAN 171 through a network interface card or adapter 170. When used in a WAN networking environment, the computer 110 typically includes a modem 172 or other means for establishing communications over the WAN 173, such as the Internet. The modem 172, which may be internal or external, may be connected to the system bus 121 via the user-input interface 160, or other appropriate mechanism. In a networked environment, program modules depicted relative to the computer 110, or portions thereof, may be stored in the remote memory storage device. By way of example, and not limitation,
It should be noted that the concepts herein described can be carried out on a computer system such as that described with respect to
As indicated above, one concept herein described provides for the analysis of words to hypothesize the language of origin. Analysis includes using N-grams of frequently used letter clusters or chunks.
As indicated above, each N-gram model of the plurality 204 is based on letter chunks or clusters. Unlike a letter based N-gram model that uses a letter as the unit for training, and hence an observation window that is narrow, a letter chunk based N-gram model allows multiple letters, a letter sequence or portion of the word (which can vary in length) to be the unit for training (i.e., a non-uniform unit); therefore, a wider observation window is provided. The wider and variable observation window allows characteristic letter chunks, or at least letter chunks that are used more frequently in a language, to be used in language of origin determination. For instance, the letter chunk ‘son’ is frequently used in English (such as in “Johnson” and “Thompson”), and therefore, may be helpful in eliminating other languages where this letter chunk is not used as frequently, if at all. Likewise, a word with ‘mann’ and/or ‘berg’ (e.g. “Bergemann”) may indicate German as the language of origin, while ‘jean’ can be useful in determining that the word is probably French (e.g. “Jeanloup”). Letter chunks can be generated by adopting various criteria. MDL (Minimum Description Length) and LZ (Lempel-Ziv) is one known criteria that has been widely used in information coding, which can also be used herein. MDL is described by J Goldsmith, in “Unsupervised Learning of the Morphology of a Natural Language,” Computational Linguistics, 27(2), pp 153-198, 2001.
The Lempel-Ziv (LZ) algorithm, which has been used in text compression, can also be used to extract letter chunks. The LZ algorithm is described by J. Ziv, and A. Lempel, in “A Universal Algorithm for Sequential Data Compression,” IEEE transactions on information theory, 23(3) pp 337-343, 1977. Referring to
Mutual information (MI) among letters can also be a good measure of the co-appearance of succeeding letters. It can be used to identify letter chunks (not necessarily syllables) in a lexicon. The process of identifying letter associations is similar to that of finding word semantic associations. Referring to
The following equation can be used to calculate MI:
where, u1, u2 is a pair of succeeding units; M is the total number of units in the training set; and N(ui) is the occurrence count of unit ui in the training set.
However, a new criterion: syllable-based letter chunk (SBLC) can also be used. Although the chunks generated with these criteria perform similar when they are used individually, each has its own strength. Therefore, the results from different chunk sets can also be combined, herein represented by combined classifier 206, to determine the language of origin.
It is believed that in most languages, syllables are stable, natural units that carry more language origin than letters. However, in normal TTS (text-to-speech) lexicon, syllable marks are only available in the phoneme string not the letter-string. Therefore, letters may need to be aligned to phonemes to obtain syllable boundaries.
One method for obtaining letter to phoneme alignment is carried out by an iterative Viterbi algorithm, for example as described by L. Jiang, H. W. Hon, X. D. Huang, in “Improvements on a trainable letter-to-sound converter,” In Proc. EUROSPEECH, pp 605-608, 1997. In this algorithm, grapheme and phoneme nulls are inserted to ensure one-to-one mapping between letters and phonemes. Then all null grapheme to phoneme pairs are merged with their neighbor pairs and this results in one to one, or one to multiple mapping between letter and phoneme. After the alignment, syllable boundaries marked in phoneme string can be copied directly to the lettering stings.
Sometimes letters are aligned to null phonemes in the result. If such pairs are located at syllable boundaries, it is difficult to judge which syllable they belong to. If desired, a rule can be employed such that letter to null phoneme pairs always belong to the syllable before it. but is at the boundary of syllables. Using the rule above, the letters “ee” are associated with the forward syllable at phoneme level. After alignment processing, the syllables of this name on the phoneme level are indicated at 504, while at the letter level are: “a ryee tey” and indicated at 506.
As is appreciated, the total number of syllables in some languages such as western languages is often very large and may not be a closed set. However, it may be necessary to use a finite set of letter chunks in view of processing constraints. Accordingly, using a finite set of letter chunks with frequencies higher than a pre-set threshold or the top “K” letter chunks in a list sorted in descending order of frequency, can be used as base units (herein referred to as “core SBLC”), in N-gram training. The number K is correlated to the overall syllable coverage.
Syllable chunks of valid syllables for pictography languages can also be ascertained. Referring to Chinese by way of example, most Asian languages are character based and each character has a fixed sound when they are written in Romanized letter(s). For example, the first name “Xiaodong” can be decomposed to “Xiao.dong”, where each syllable has its corresponding character respectively. Therefore, “xiao” and “dong” can be considered valid syllables for Chinese. Consequently, even though the number of consonants and vowels may be as many or much more than English or other western or European languages, the combinations of consonants and vowels in a syllable are fixed. In other words, it is a closed-set. For example, there are only about 400-500 possible syllables for Mandarin Chinese and about 100-150 possible syllables for Japanese. This applies to other languages (in particular other Asian languages) that use pictographs in their native language, each of which can be converted to Romanized letter sequences.
Since a closed set of syllables is present, this characteristic can be used advantageously. In particular, it is possible to detect “valid” letter chunks with greater confidence based on the closed set, while rejecting possible words when it contains letter sequences that can't be decomposed to a valid letter chunk.
After ascertaining a set of letter chunks, an N-gram model can be trained for the language from a given lexicon. Referring first to SBLC, the training of a SBLC N-gram is quite similar to the training of a letter based N-gram except that, because only part of possible SBLCs in a language are covered by the core SBLC list, the parts not covered can be decomposed by the following rules:
To build a list of valid syllables for pictography languages, one uses a lexicon with the pictograph/character and their corresponding Romanized letter sequence. Entries from a Chinese lexicon are provided below by way of example: _→
→
→
→
The unique letter sequences in the second column are collected and used as valid syllables; thus, forming the closed set of valid syllables. However, it should be noted that other pictographs may correspond to the same Romanized letter sequence. Typically, the amount of the valid pictographs may be large, but they still comprise a closed set. Moreover, the set of corresponding Romanized syllables is much smaller. Words in a dictionary can then be decomposed into strings consisting of valid syllables, from which N-grams are trained. For example: he xiao dong
It should be noted that since multiple chunk sets can be generated with different criteria (MDL, MI, LZ, SBLC, closed set of valid syllables, etc.), multiple N-gram models can be obtained for each language as represented by the multiple N-Gram models (N) provided for each language (M) in
p(w/l)=p(s1,s2, . . . ,sn/l)
If tri-gram analysis is adopted, by way of example, the equation can be rewritten as:
Of course, other forms of N-gram analysis can be used. Normally, there are many possible paths for the segmentation. Searching for the best path is similar to word segmentation with N-gram. For example, when adopting SBLC, the word ‘aryeetey’ can be segmented to n paths with letter chunks from the core SBLC list.
Name: a r y e e t e y
Path1: a ryee tey
Path2: ar yee tey
. . .
Pathn: a ry ee tey
The final path is the one with the highest likelihood for the given N-gram model, where the score is the final likelihood for w belongs to 1.
A probability is ascertained that the word is from a language based on the N-gram model(s) at step 604. As exemplified herein a score is calculated with each N-gram model, for each language, if so provided. At step 606, an output hypothesis is obtained based on the ascertained probability. In one embodiment, a simple way to obtain a hypothesis of the language origin of the word is to assign it to the language origin of the N-gram model that got the highest likelihood. Although this technique will provide a hypothesis for the language of origin, further processing of the scores at step 606 can be performed to provide the hypothesis.
Since the error distributions of N-grams of letter chunks generated with different criteria are different, the scores of multiple N-grams can be merged as shown in
The combined classifier 206 can take any number of forms including Naïve Bayesian decision processing, voting, use of CART (Classification and Regression Tree), use of GMMs (Gaussian Mixture Model) or AdaBoost (adaptive boosting). These techniques are investigated below to identify language origin from the LXM dimension likelihood vector of a word, where L is the number of candidate languages and M is the number of chunk sets per language.
Use of Naïve Bayesian decision can be used to combining results from multiple classifiers. Using this technique, the word is assigned to the language that has a chunk model which achieves the highest likelihood among the L×M scores.
Voting is another simple method to combine different classifiers, i.e. assigning the word to the language that gets the highest vote from all chunk models. If there are two languages getting the same number of votes, the one with the highest likelihood is chosen.
Classification and Regression Tree (CART) is a widely used classifier. This standard statistical method can be used to predict both categorical and continuous data from a set of feature vectors. The tree itself contains yes/no questions about features and ultimately provides either a probability distribution, when predicting categorical values (classification tree), or a mean and standard deviation when predicting continuous values (regression tree). CART can be used to predict the language origin directly from scores of multiple chunk N-grams.
Gaussian Mixture Model (GMM) models the probability density function of observed variables using a multivariate Gaussian mixture density. Given a series of inputs, it refines the weights of each distribution through expectation-maximization algorithms. In the present application, the scores from multiple chunk models are treated as an eigenvector of a word and a GMM is built for each language with such features. When a new word is presented, it is scored by all GMMs and the language corresponding to the highest likelihood is chosen.
AdaBoost is well known and is widely used for combining weak classifiers. Briefly, this algorithm begins by building an initial model from the training dataset. Then, incorrectly classified records are identified and used to train a new model which boosts the importance of these problematic records in the training process. By way of example and in one embodiment, the one dimension naïve Bayesian classifier is adopted as the weak classifier.
Although AdaBoost is designed for two class separation, it is known to make it suitable for multi-class problem. One-against-all is the most popular one and can be used herein. In the one-against-all method for a M class problem, M classifiers are trained. For instance, a classifier is trained for each language under consideration for the language origin of the word. In
In an alternative form, Adaboost.ecc can be used to handle the multi-classes problem since it may be better than the one-against-all method. Briefly, for a P-class classification problem, each class is assigned an associated code C=(c1, . . . , cQ) ciε{1,−1}, with length Q (Q>P). For each bit Ci, the label is two-class, then the P-class problem becomes Q independent two-class problems. The code can be designed as error correcting code and the redundant information in the code can improve the robustness of the two-class classifiers.
In the ECC framework, for a sample x and class C, there are Q classifiers with outputs f1(x), . . . , fQ(x). The posterior probability of class C is,
When a word is presented, it is recognized by the Q classifiers. The posterior probability of each language is calculated from the previous equation. The hypothesis with highest posterior probability will be the final output.
Language processing system 700 includes a language of origin ascertaining module 702 as herein described for ascertaining the language of origin of selected words.
As appreciated by those skilled in the art, the language of origin ascertaining module 702 can be used in other language processing systems besides the speech synthesizer discussed above. For instance, the language of origin ascertaining module 702 can also be used with speech recognition systems to improve accuracy. However, it should be noted whether the top choice is used, or whether the top “n” choices are used, may depend upon the application. For instance, when module 702 is used in conjunction with a speech synthesizer generally the top choice is used since there exists one opportunity for pronunciation. In contrast, when module 702 is used with speech recognition, use of more than just the top choice may improve recognition. For example, if the speech recognizer uses the top two results, recognition can proceed based on two languages, thereby providing a higher chance of correct name recognition.
Other types of language processing systems 700 include machine translation systems. In particular, machine translation will be able to do a better job when the language origin is known, where the language of origin information allows choice of a suitable set of localized words for the word to be translated. For example, suppose module 702 receives the name “Taro Miwa” in English text as input 712, and attempts to translate it into Chinese as output 714. If upon analysis it is first determined that the input text 712 is Japanese, the appropriate Kanji representation can be found and translated to the correct Chinese name, instead of translating it by matching sound, for example realizing,
which although sounds closer, is not the correct translation for the inputted Japanese name.
The language processing system 700 can also be used as an aid during testing. For example, the language processing system 700 can receive multi-language words such as personal names and group the words as native or foreign names to ascertain the performance differences between the native and non-native groups. If the performance of an engine (speech synthesizer, speech recognizer, machine translator, etc.) is doing much better on one group of words than the other, this information can be reported to the engine developers. In particular, if the foreign names are organized into more specific language groups, it will help to know which language caused the most problems, thereby focusing development of the engine with that language.
Some language processing systems may include both speech recognition and speech synthesis. For example, an automated telephone call receptionist is required to recognize the name of the desired person the caller is trying to reach. Commonly, this process will also include pronouncing the recognize name in order to obtain confirmation. User frustration can result if the caller perceives an error due to mispronunciation. In particular, the caller may give up in just a few tries if the speech synthesizer continually mispronounces the recognize name even if the speech recognizer did indeed recognize the correct name. In this embodiment, the language processing system 700 can receive lists of foreign words, such as names, and identify the language of origin of each name. The ascertained language of origin can then be included in the grammar, such as a context free grammar (CFG) and used by the speech recognizer and/or speech synthesizer.
Although the subject matter has been described in language specific to structural features and/or methodological acts, it is to be understood that the subject matter defined in the appended claims is not limited to the specific features or acts described above as has been held by the courts. Rather, the specific features and acts described above are disclosed as example forms of implementing the claims.
