IOB tagging system is one of the convention for NER.
The IOB Tagging system contains tags of the form:
- B-{CHUNK_TYPE}: for the word in the Beginning chunk
- I-{CHUNK_TYPE}: for words Inside the chunk
- O: Outside any chunk
- B-PERSON : Person Entity
- B-GPE : Geopolitical Entity
Th following text shows example of a names entities in a sentence:
John has lived in Britain for 14 years . B-PERSON O O O B-GPE O B-CARDINAL I-CARDINAL O
However, it is quite challenging due to two reasons:
- Entity databases are often incomplete (given the number of new organizations being established)
- The same phrase can refer to a different entity (or none entity) depending on the context
