Question: What model do they compare the ZAT model with?
Evidence: Recently, there is a surge of excitement in adding numerous new domains to conversational agents such as Alexa, Google Assistant, Cortana and Siri to support a myriad of use cases. However, building a slot tagger, which is a key component for natural language understanding (NLU) BIBREF0 , for a new domain requires massive amounts of labeled data, hindering rapid development of new skills. To address the data-intensiveness problem, domain adaptation approaches have been successfully applied. Previous approaches are roughly categorized into two groups: data-driven approaches BIBREF1 , BIBREF2 and model-driven approaches BIBREF3 , BIBREF4 .
In the data-driven approach, new target models are trained by combining target domain data with relevant data from a repository of arbitrary labeled datasets using domain adaptation approaches such as feature augmentation BIBREF1 . A disadvantage of this approach is the increase in training time as the amount of reusable data grows. The reusable data might contain hundreds of thousands of samples, making iterative refinement prohibitive. In contrast, the model-driven approach utilizes “expert" models for summarizing the data for reusable slots BIBREF3 , BIBREF4 . The outputs of the expert models are directly used when training new domains, allowing for faster training. A drawback of this approach is that it requires explicit concept alignments which itself is not a trivial task, potentially missing lots of reusable concepts. Additionally, it's not easy to generalize these models to new, unseen slots.
In this paper, we present a new domain adaptation technique for slot tagging inspired by recent advances in zero-shot learning. Traditionally, slot tagging is formulated as a sequence labeling task using the BIO representation (Figure 1 ). Our approach formulates this problem as detecting spans that contain values for each slot as shown in Figure 1 . For implicit transfer of reusable concepts across domains, we represent slots in a shared latent semantic space by embedding the slot description. With the shared latent space, domain adaptation can simply be done by fine-tuning a base model, which is trained on massive data, with a handful of target domain data without any explicit concept alignments. A similar idea of utilizing zero-shot learning for slot tagging has been proven to work in semi-supervised settings BIBREF5 . Our zero-shot model architecture differs from this by adding: 1) an attention layer to produce the slot-aware representations of input words, 2) a CRF layer to better satisfy global consistency constraints, 3) character-level embeddings to incorporate morphological information. Despite its simplicity, we show that our model outperforms all existing methods including the previous zero-shot learning approach in domain adaptation settings.
We first describe our approach called Zero-Shot Adaptive Transfer model (ZAT) in detail. We then describe the dataset we used for our experiments. Using this data, we conduct experiments comparing our ZAT model with a set of state-of-the-art models: Bag-of-Expert (BoE) models and their non-expert counterparts BIBREF4 , and the Concept Tagger model BIBREF5 , showing that our model can lead to significant F1-score improvements. This is followed by an in-depth analysis of the results. We then provide a survey of related work and concluding remarks.
Using this data, we conduct experiments comparing our ZAT model with a set of state-ofthe-art models: Bag-of-Expert (BoE) models and their nonexpert counterparts (Jha et al. 2018), and the Concept Tagger model (Bapna et al. 2017), showing that our model can lead to significant F1-score improvements.
Answer: Bag-of-Expert (BoE) models and their non-expert counterparts , and the Concept Tagger model.