The North-T5 is a set of Norwegian sequence-to-sequence-models. It builds upon the flexible T5 text-to-text platform and can be used for a variety of NLP tasks ranging from classification to translation.
| Model: | Parameters | Transformers | T5X |
|---|---|---|---|
| North-T5-small | 60 million | HuggingFace | GCloud Bucket |
| North-T5-base | 220 million | HuggingFace | GCloud Bucket |
| North-T5-large | 770 million | HuggingFace | GCloud Bucket |
| North-T5-xl | 3 billion | HuggingFace | GCloud Bucket |
| North-T5-xxl | 11 billion | N/A | GCloud Bucket |
A thorough evaluation of the North-T5 models is planned. I strongly recommend any external researchers to make their own evaluation. The main advantage with the T5-models are their flexibility. Traditionally, encoder-only models (like BERT) excels in classification tasks, while seq-2-seq models are easier to train for tasks like translation and Q&A. Despite this, here are the results from using North-T5 on the political classification task explained here.
| Model: | F1 |
|---|---|
| mT5-base | 73.2 |
| mBERT-base | 78.4 |
| NorBERT-base | 78.2 |
| North-T5-small | 80.5 |
| nb-bert-base | 81.8 |
| North-T5-base | 85.3 |
| North-T5-large | 86.7 |
| North-T5-xl | 88.7 |
| North-T5-xxl | 91.8 |
This is preliminary results. The results from the BERT-models are based on the test-results from the best model after 10 runs with early stopping and a decaying learning rate. The T5-results are the average of five runs on the evaluation set. The small-model was trained for 10.000 steps, while the rest for 5.000 steps. A fixed learning rate was used (no decay), and no early stopping. Neither was the recommended rank classification used. We use a max sequence length of 512. This method simplifies the test setup and gives results that are easy to interpret. However, the results from the T5 model might actually be a bit sub-optimal.
For making it possible to run experiments on the T5-models, a range of sub-versions are released. These models are currently only available as base-models. However, other model sizes can be made available by request.
| Model: | Description |
|---|---|
| North-T5-base-LM | Pretrained for an addtional 100k steps on the LM objective described in Raffel & al. In a way this turns a masked language model into an autoregressive model. It also prepares the model for some tasks. When for instance doing translation and NLI, it is well documented that there is a clear benefit to do a step of unsupervised LM-training before starting the finetuning. |
| North-byT5-base | A vocabulary free version of T5. Trained exactly like North-T5, but instead of the 200.000 vocabulary, this model operates directly on the raw text. The model architecture might be of particulary interest for tasks involving for instance spelling correction, OCR-cleaning, handwriting recognition etc. However, it will, by design, have a shorter maximum sequence length. |
| North-T5-base-modern | Pretrained for an additional 200k steps on a blanaced Bokmål and Nynorsk corpus. While original made for doing translation between Bokmål and Nynorsk, it might also give improved results on tasks where you know that the input/output is modern "standard" text. A significant part of the training corpus is newspapers and reports. |
| North-T5-base-scandinavian | Pretrained for an additional 200k steps on a corpus with the Scandinavian languages (Bokmål, Nynorsk, Danish, Swedish and Icelandic (+ a tiny bit Faeroyish)). The model was trained for increasing the understanding of what effect such training has on various languages. |
As explained below, the model really needs to be fine-tuned for specific tasks. This procedure is simple, and the model is not very sensitive to the hyper-parameters used. Usually a decent result can be obtained by using a fixed learning rate of 1e-3. Smaller versions of the model typically needs to be trained for a longer time. It is easy to train the base-models in a Google Colab. I will provide an exampel Notebook on this soon.
Since some people really want to see what the models are capable of, without going through the training procedure, I provide a couple of test models. These models are by no means optimised, and are just for demonstrating how the North-T5 models can be used.
- Nynorsk Translator. Translates any text from Norwegian Bokmål to Norwegian Nynorsk.
- De-Uncaser. Puts punctation, spaces and capital letters back into the text. The input needs to be in Norwegian but does not have to be divided into sentences or have proper capitalisation of words. You can even remove the spaces from the text, and make the model reconstruct it.
The models are built using the Flax-based T5X codebase, and all models are initiated with the mT5 pretrained weights. The models are trained using the T5.1.1 training regime, where they are only trained on an unsupervised masking-task. This also means that the models (contrary to the original T5) needs to be finetuned to solve specific tasks. This finetuning is however usually not very compute intensive, and in most cases it can be performed even with free online training resources.
All the main model model versions are trained for 500.000 steps after the mT5 checkpoint (1.000.000 steps). They are all trained mainly on a 75GB corpus, consisting of NCC, Common Crawl and some additional high quality English text (Wikipedia). The corpus is roughly 80% Norwegian text. Additional languages are added to retain some of the multilingual capabilities, making the model both more robust to new words/concepts and also more suited as a basis for translation tasks.
While the huge models almost always will give the best results, they are also both difficult and expensive to finetune. It is strongly recommended to start with finetuning on a base-models. This can typically easily be finetuned on a standard graphic card or a free TPU through Google Colab. The sub-versions of the North-T5-base model was created with this in mind.
All models were trained on TPUs. The largest XXL model was trained on a TPU v4-64, the XL model on a TPU v4-32, the Large model on a TPU v4-16 and the rest on TPU v4-8.
All models are trained using the Flax-based T5X library. The original checkpoints are available in T5X format and can be used for both finetuning or interference. All models, except the XXL-model, are also converted to Transformers/HuggingFace. In this framework, the models are available both in Flax, PyTorch and TensorFlow format.
I will continue to train and release additional models to this set. What models that are added is dependent upon the feedback.
This release would not have been possible without getting support from TPU Research Cloud at Google Research.
Freddy Wetjen at the National Library of Norway has been of tremendous help in generating the original NCC corpus, and has also contributed to generate the collated coprus used for this training. In addition he has been a dicussion partner in the creation of these models.
Also thanks to Stefan Schweter for writing the script for converting these models from T5X to HuggingFace and to Javier de la Rosa for writing the dataloader for reading the HuggingFace Datasets in T5X.
Use at your own risk. The models have not yet been thougroughly tested, and may contain both errors and biases.
These models were trained by Per E Kummervold. Please contact me on per@capia.no.