Few-shot nested named entity recognition (NER), identifying named entities that are nested with a small number of labeled data, has attracted much attention. Recently, a span-based method based on three stages ( focusing, bridging and prompting) has been proposed for few-shot nested NER. However, such a span-based approach for few-shot nested NER suffers from two challenges: 1) error propagation because of its 3-stage pipeline-based framework; 2) ignoring the relationship between inner and outer entities, which is crucial for few-shot nested NER. Therefore, in this work, we propose a two-stage approach with a controllable attention soft prompt for few-shot nested named entity recognition (TECA). It consists of two components: span part identification and entity mention recognition. The span part identification provides possible entity mentions without an extra filtering module. The entity mention recognition pays fine-grained attention to the inner and outer entities and the corresponding adjacent context through the controllable attention soft prompt to classify the candidate entity mentions. Experimental results show that the TECA approach achieves state-of-the-art performance consistently on the four benchmark datasets (ACE2004, ACE2005, GENIA, and KBP2017) and outperforms several competing baseline models on F1-score by 5.62% on ACE04, 5.11% on ACE05, 3.41% on KBP2017 and 0.7% on GENIA on the 10-shot setting.

Few-shot named entity recognition (NER), identifying named entities with a small number of labeled data, has attracted much attention. Frequently, entities are nested within each other. However, most of the existing work on few-shot NER addresses flat entities instead of nested entities. To tackle nested NER in a few-shot setting, it is crucial to utilize the limited labeled data to mine unique features of nested entities, such as the relationship between inner and outer entities and contextual position information. Therefore, in this work, we propose a novel method based on focusing, bridging and prompting for few-shot nested NER without using source domain data. Both focusing and bridging components provide accurate candidate spans for the prompting component. The prompting component leverages the unique features of nested entities to classify spans based on soft prompts and contrastive learning. Experimental results show that the proposed approach achieves state-of-the-art performance consistently on the four benchmark datasets (ACE2004, ACE2005, GENIA and KBP2017) and outperforms several competing baseline models on F1-score by 9.33% on ACE2004, 6.17% on ACE2005, 9.40% on GENIA and 5.12% on KBP2017 on the 5-shot setting.