This article was published as a part of the Data Science Blogathon.

Natural Language Processing (NLP) is a sur speech.

NLP task includes :

Speech Recognition: It is the task of converting voice data to text data. It is used in chatbots, voice search systems, voice commands to IoT devices, etc.

Sentiment Analysis: Sentiment analysis (aka Opinion mining) is an NLP technique used to determine whether a given sentence/phrase delivers a positive, negative, or neutral message.

Named Entity Recognition: It is also known as NER. It is used to extract entities using pre-trained categories.

In this article, we will be focusing on Named Entity Recognition(NER) and its real-world use cases, and in the end, we will train our custom model using HuggingFace embeddings.

What is NER?

NER (Named Entity Recognition), in simple words, is one of the key components of NLP (Natural Language Processing) used for the recognition and extraction of entities with predefined(or pre-trained) categories from a plain/unstructured text.

These entities can be anything like Person’s Name, Location, Organization, Country, City, etc., depending on the categories we train our model on.

Let’s take an example:

In the above example, the model can extract PERSON, ORGANIZATION & LOCATION entities in the example.

Yes, indeed, it’s the magic of NER. 😎

In this article, we will go through the basic definition of NER and its use cases and train our own custom NER model using Hugging Face Flair embeddings.

But where can we use NER in the real world?🤔

NER Applications & Use Cases

1) Efficient search algorithms: NER can be used to extract relevant entities from search queries for better search results.

2) Resume parsing: In various companies & MNCs, NER is used for resume parsing by extracting relevant information about the candidate appearing for the job to filter out the best possible candidate among thousands of applicants.

3) PII (Personal Identifiable Information) extraction: Protecting the user’s personal information is one of the crucial tasks that every company needs to take care of. NER helps extract PII entities such as Name, DOB, Credit Card Number, SSN, Phone Number, etc., so they can be masked.

4) Chatbot: Most typical usage of NER is a chatbot. Chatbots use NER to extract keywords for answering user queries.

Etcetera etcetera

Yupp!! Now let’s train our model 🤘😎🤘

We will use Hugging Face(not this 🤗) flair embedding to train our own NER model.

Hugging Face is a company that provides open-source NLP technologies. It has significant expertise in developing language processing models.

Training Custom NER Model using HuggingFace Flair Embedding

There is just one problem…NER needs extensive data for training.

But we don’t need to worry, as CONLL_03 comes to the rescue!!!

CoNLL-2003 consists of a large annotated and unannotated dataset for training , testing and validation.

You can read more about CONLL_03 here.

Before starting the training, we must know the format of the NER training data.

The NER dataset should contain two columns separated by a single space. The first column consists of a single word followed by the Named Entity Tag in the second column.

Note : Column 1 must contain a single word.

Note : CONNL_03 consists of 4 columns.
Column 1 containing individual word.
Column 2 part-of-speech tag
Column 3 syntactic chunk tag
Column 4 named entity tag
In most of the cases column 2 and 3 are omitted as they are optional.

Let’s take an example :

Let the text be “George Washington went to Washington.“

So the format would be :

George B-PER
Washington I-PER
went O
to O
Washington B-LOC

Okay, I see you are confused. Don’t worry. Let me explain.

You might be wondering WHAT THE HELL IS THIS B-PER AND I-PER !!

B -> stands for Beginning

I -> stands for intermediate

So, if any phrase consists of related words, then we use the annotations.

Example: George Washington

Here, George is the first name, and Washington is the last name.

So, for NER to know that these types of words should come together while running the model on a piece of text, we prefix such words with B- or I- followed by the tag (PER, LOC, ORG, etc.) while creating our dataset.

Also, it will help or model to differentiate between 2 similar entities. Like in the above example, Washington in George Washington is the last name and also a location.

Another example: The United States of America

United B-LOC
States I-LOC
of I-LOC
America I-LOC

That is all you need to know about your dataset before training your own custom NER model!!!

So now let’s break some keys ;

The Code

Installing flair :

Flair is a Huggingface embedding used to perform various ML/AI tasks.

To install the flair embedding, we use the following command:

pip install flair

Imports :

We need to import the following classes & embeddings 

from flair.data import Corpus
from flair.datasets import CONLL_03
from flair.embeddings import WordEmbeddings, StackedEmbeddings, FlairEmbeddings

Here,

corpus: Corpus = CONLL_03()

tag_type = 'ner'

tag_dictionary = corpus.make_tag_dictionary(tag_type=tag_type)

embedding_types = [
    # GloVe embeddings
    WordEmbeddings('glove'),
    # contextual string embeddings, forward
    FlairEmbeddings('news-forward'),
    # contextual string embeddings, backward
    FlairEmbeddings('news-backward'),
]

embeddings = StackedEmbeddings(embeddings=embedding_types)

from flair.models import SequenceTagger
tagger = SequenceTagger(hidden_size=256,
                    embeddings=embeddings,
                    tag_dictionary=tag_dictionary,
                    tag_type=tag_type)

from flair.trainers import ModelTrainer
trainer = ModelTrainer(tagger, corpus)

trainer.train('resources/taggers/ner-english',
                       train_with_dev=True,
                       max_epochs=150)

from flair.data import Sentence
from flair.models import SequenceTagger

model = SequenceTagger.load('resources/taggers/ner-english/final-model.pt')

sentence = Sentence("George Washington lives in Washington")

model.predict(sentence)

for entity in sentence.get_spans('ner'):
    print(entity)

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