CRF-NER

Conditional Random Fields

Labelling

Label format is an important step to do. There are several different labellings. IO (Inside-Outside) tagging is easy, if the word is a named entity, it is tagged as I-xxx, ortherwise O. IOB (Inside-Outside-Beggining) tagging is extended version of IO tagging. The beggining word of the named entity is tagged as B-xxx and following words of the entity are tagged as I-xxx. Other words are tagged as O (O for out).

Example: Türkiye --> B-ORG
Cumhuriyeti --> I-ORG
1923 --> O
yılında --> O
kurulmuştur. --> O
İlk --> O
cumhurbaşkanı --> O
Mustafa --> B-PER
Kemal --> I-PER
Atatürk'tür. --> I-PER
Başkenti --> O
Ankara'dır. --> B-LOC

CRF features:

• Root (Stem)
• Part-of-Speech (POS)
• Proper Noun (PROP)
• Noun Case (NCS)
• Orthographic Case (OCS)
• All Inflectional Features (INF)
• Start of the Sentence (SS)

Result

F1 Scores
CRF1 --> 0.8485571904592357
CRF2 --> 0.8402884363601334
CRF3 --> 0.8467095943830918
CRF4 --> 0.8105135631724366
CRF5 --> 0.845174444670488
Average --> 0.8382486458090771