What are training and modeling?
A model is the system, which provides translation for a specific language pair. The outcome of a successful training is a model. To train a model, three mutually exclusive document types are required: training, tuning, and testing. Dictionary document type can also be provided. For more information, see Sentence alignment.
If only training data is provided when queuing a training, Custom Translator will automatically assemble tuning and testing data. It will use a random subset of sentences from your training documents, and exclude these sentences from the training data itself.
Training document type for Custom Translator
Documents included in training set are used by the Custom Translator as the basis for building your model. During training execution, sentences that are present in these documents are aligned (or paired). You can take liberties in composing your set of training documents. You can include documents that you believe are of tangential relevance in one model. Again exclude them in another to see the impact in BLEU (Bilingual Evaluation Understudy) score. As long as you keep the tuning set and test set constant, feel free to experiment with the composition of the training set. This approach is an effective way to modify the quality of your translation system.
You can run multiple trainings within a project and compare the BLEU scores across all training runs. When you're running multiple trainings for comparison, ensure same tuning/ test data is specified each time. Also make sure to also inspect the results manually in the "Testing" tab.
Tuning document type for Custom Translator
Parallel documents included in this set are used by the Custom Translator to tune the translation system for optimal results.
The tuning data is used during training to adjust all parameters and weights of the translation system to the optimal values. Choose your tuning data carefully: the tuning data should be representative of the content of the documents you intend to translate in the future. The tuning data has a major influence on the quality of the translations produced. Tuning enables the translation system to provide translations that are closest to the samples you provide in the tuning data. You don't need more than 2500 sentences in your tuning data. For optimal translation quality, it's recommended to select the tuning set manually by choosing the most representative selection of sentences.
When creating your tuning set, choose sentences that are a meaningful and representative length of the future sentences that you expect to translate. Choose sentences that have words and phrases that you intend to translate in the approximate distribution that you expect in your future translations. In practice, a sentence length of 7 to 10 words will produce the best results. These sentences contain enough context to show inflection and provide a phrase length that is significant, without being overly complex.
A good description of the type of sentences to use in the tuning set is prose: actual fluent sentences. Not table cells, not poems, not lists of things, not only punctuation, or numbers in a sentence - regular language.
If you manually select your tuning data, it shouldn't have any of the same sentences as your training and testing data. The tuning data has a significant impact on the quality of the translations - choose the sentences carefully.
If you aren't sure what to choose for your tuning data, just select the training data and let Custom Translator select the tuning data for you. When you let the Custom Translator choose the tuning data automatically, it will use a random subset of sentences from your bilingual training documents and exclude these sentences from the training material itself.
Testing dataset for Custom Translator
Parallel documents included in the testing set are used to compute the BLEU (Bilingual Evaluation Understudy) score. This score indicates the quality of your translation system. This score actually tells you how closely the translations done by the translation system resulting from this training match the reference sentences in the test data set.
The BLEU score is a measurement of the delta between the automatic translation and the reference translation. Its value ranges from 0 to 100. A score of 0 indicates that not a single word of the reference appears in the translation. A score of 100 indicates that the automatic translation exactly matches the reference: the same word is in the exact same position. The score you receive is the BLEU score average for all sentences of the testing data.
The test data should include parallel documents where the target language sentences are the most desirable translations of the corresponding source language sentences in the source-target pair. You may want to use the same criteria you used to compose the tuning data. However, the testing data has no influence over the quality of the translation system. It's used exclusively to generate the BLEU score for you.
You don't need more than 2,500 sentences as the testing data. When you let the system choose the testing set automatically, it will use a random subset of sentences from your bilingual training documents, and exclude these sentences from the training material itself.
You can view the custom translations of the testing set, and compare them to the translations provided in your testing set, by navigating to the test tab within a model.