NER Models not using BIO tagging scheme
Hello,

I have noticed that most (all?) pre-trained models uploaded seem not to use the BIO tagging scheme, instead returning `I-xxx` and `O` for all categories (`B-xxx` is not used). I believe this is just caused by the way these models have been trained. This makes using these models in actual pipelines difficult as entity parsing becomes impossible (two consecutive entities cannot be differentiated from a multi-tokens entity). 

Are there any plans for updating these models with a BIO labelling scheme?
@stefan-it including you in the discussion as you have uploaded standard models used in the default pipelines
Hi @guillaume-be , only the CoNLL-2003 models are using this IOB1 tagging scheme, because it is used in the original dataset. You could convert it (+ needs proper testing) but this requires a modification of the original dataset.

I could train models e.g. on the WikiANN corpus (see [here](https://www.aclweb.org/anthology/P17-1178/) and WikiANN with balanced train/dev/test splits [here](https://www.aclweb.org/anthology/P19-1015/)) for English, but this corpus is then just a "silver standard" :)<|||||>Hi @stefan-it ,

Thank you for your response. Assuming the CoNLL-03 model is in IOB1 tagging scheme, it would still use `B-*` labels in case of multi-token entities. For example:
```
Alex I-PER
is O
going O
to O
Los B-LOC
Angeles I-LOC
```
However, the model currently outputs the following for this example:
```
Alex I-PER
is O
going O
to O
Los I-LOC
Angeles I-LOC
```

This means that it is impossible to differentiate multi-token entities (such as Los Angeles) from multiple consecutive entities, e.g. `Alex Bob and Amy are going to Los Angeles`. So far I have never seen the model uploaded generate a `B-*` token. <|||||>`B-*` is only used when an entity follows right after another entity, e.g. different political parties, like this example from the training dataset:

```bash
MAY NNP I-NP O
1996 CD I-NP O
CDU NNP I-NP I-ORG
/ SYM O I-ORG
CSU NNP I-NP I-ORG
SPD NNP I-NP B-ORG
FDP NNP I-NP B-ORG
Greens NNP I-NP B-ORG
PDS NNP I-NP B-ORG
```

Just have a look at the last column. `CDU/CSU` can be considered as one entity, but right after it another political party `SPD` is followed, so it is tagged with a beginning `B-` :)<|||||>@stefan-it thank you for the clarification!<|||||>@stefan-it are there plans to [merge this pr](https://github.com/huggingface/transformers/pull/3957)? it could help with this issue. i have it myself as i need to pool entity embeddings. https://github.com/huggingface/transformers/issues/3548<|||||>@petulla Should be merged soon 👍 