What is Named Entity Recognition (NER)? What annotation is most commonly used (BIO, BIOES)?

Named Entity Recognition (NER) is a task in the field of natural language processing (NLP) aimed at automatically identifying and classifying named entities in text, such as people's names, organizations, dates, locations, etc.

For sequence labeling in NER, schemes like BIO and BIOES are often used:

• BIO (Begin, Inside, Outside): labels indicate whether a token is the beginning of an entity (B), inside an entity (I), or outside any entity (O).
• BIOES (Begin, Inside, Outside, End, Single): an extended scheme that adds labels for the end of an entity (E) and single-token entities (S). This helps in more accurately defining entity boundaries.

BIO and BIOES help models understand the structure and boundaries of named entities in text.